Liquid level indicator

[MarkMc]

For my home brewery I need to know if a container has liquid past a
certain level, and if it is, turn on a pump.

Can anybody suggest a way of doing this? I don't really want to use
anything which floats in the liquid, I just need to know if the liquid
is past a certain point/level.

If there's anything "off the shelf" which I can screw in to the
container, then that would be fantastic.

Regards,
Mark

 

[Chris]

John Popelish wrote:

You might Google "capacitive proximity". These are devices that
switch an output signal when conductive material gets close to their
face. Some can operate through glass or plastic container walls.
http://www.turck-usa.com/products/sensors/capacitive/Barrel_with_Potted-in_Cable/

Home brew electronics for home brew beer -- it's s.e.b. synergy!

Mr. Popelish's suggestion is a great choice. But you might want to
reconsider the float concept. Many small floats are made for food
service (i.e. they can be washed down, scrubbed and sterilized), and
the built-in hysteresis of a magnetic float can make this the easiest
solution. If you can't do that for one reason or another, you still
have a number of options, besides the capacitive sensor. They''re all
going to be more expensive and more difficult, though.

By placing the vat on a scale or load cells, you can weigh the vat and
its contents. But if you're going to use the information for anything,
you need some kind of output from the scale. You can get one with
serial communication output and interface to a PC. Scales are also
made with analog outputs, which might allow you to do this without a
PC. In fact, many of the simplest scales have an analog front end
feeding either an A-to-D converter with LED/LCD display, or a uC analog
input. If you're crafty, you might be able to pick that off and use it
for your control circuit. Downside, of course, is that you have to be
careful about movement (kind of hard if you've got an agitator). Also,
any motor or other equipment may have to be weighed along with the vat.

Some ultrasonic sensors are made for this and have discrimination
circuitry built in which can ignore the foam and output the result from
the strongest signal rather than the first. However, these are fairly
expensive, especially for a home brew setup. You would also have to
have the sensor face inside the tank, and cleaning/sterilization limits
your choices.

If you can live with something which goes through the wall, but is
fairly flush and also has food service rating, you might want to try
some of the retroreflective sensors made by Gems and other
manufacturers. They send out a light beam to a prism which extends
into the vat. Air and foam on the face of the prism will force almost
all of the light to reflect off the prism and back to the sensor. When
the beer comes in contact with the prism, though, most of the light
just goes straight through the glass into the liquid. Less expensive
than the ultrasonics, but you still have to pierce the vat. In
addition, there's no hysteresis, which may mean you'll have to install
two sensors.

If your vat is white Nalgene or another translucent material, you might
be able to get away with using a couple of photoresistors to sense
light through the vat itself. This might be a bit of a touchy
adjustment, though, and might be very dependent on ambient light.

There are several other much more expensive methods to level sense beer
or other foaming liquid, but I would guess they're beyond your budget.

The float is the least expensive and most efficient solution. If I
were in your shoes, I would get a Gems catalog or check out their
website and take a good look at what they have for food service floats.
IMHO, that would be your best bet if you're on a budget. And by the
way, they have live phone help from 8 to 4:30 EST M-F. If you're in a
hurry, just call them up and ask for help. They don't mind onesie
applications. You can get much of their product line sent direct from
Newark and have your solution tomorrow.

http://www.gemssensors.com/

Good luck
Chris

 

[siliconmike]

MarkMc wrote:

For my home brewery I need to know if a container has liquid past a
certain level, and if it is, turn on a pump.

Get one of those "touch to on" lamps.

Take two insulated copper wires, say 18 SWG and attach them to your
vessel in such a way that when your liquid reaches the desired level,
the two copper wires touch the liquid.

Connect the other end of one of the copper wire to earth
Connect the other end of the second copper wire to the touch lamp's
body

Connect your pump to the AC output of the touch lamp (where you're
supposed to fix a light bulb)

Connect a relay to the AC output of the touch lamp, in such a manner
that when energised, it shorts the lamp's body to earth.

Mike

 

[siliconmike]

Connect a relay to the AC output of the touch lamp, in such a manner
that when energised, it shorts the lamp's body to earth.

I meant connect energizing coil of relay to AC output of touch lamp..
(of course the relay should have an AC mains driven coil)..

This is to clamp the pump on (even after the liquid level goes down or
there are waves in the vessel).

Mike

 

[MarkMc]

Thanks for all the suggestions everybody.

I'll explore each of them individually.

I spotted these in RS #354-290. The seems to be quite a pro sort of
thing. They have a relay control unit, but I need to add a few of my
own other features, to I'd have to interface to them myself. I'm not
sure how to create an alternating voltage (flip-flop?), and evern more
so, I don't know how to measure the resistance via AC voltage/current.

Cheers,
Mark

 

[MarkMc]

Somebody on my brewing forum suggests this cct, which seems good.

http://www.uoguelph.ca/~antoon/circ/sensor3.htm

I am abit of a newbie, can anybody explain to me what's going on here?

From what I understand, a small a/c voltage is sent out, and taken back
on another probe, which is then rectified and 'compared' to a reference

level which energises the relay. Which bits of the cct do what
parts/how they do it, I'm not sure about.

I need to be able to alter this circuit by taking the logical state(0
or 1) of the sensor output, and combining it with a few other gates
before then driving the output relay.

I'm always bad at understanding transistors, and CMOS outputs. Why
does he use PNP rather than NPN here? Does it matter? Can I use say
BC107's (which I have at home) instead?

Regards,
Mark

 

[Chris]

MarkMc wrote:

Somebody on my brewing forum suggests this cct, which seems good.

http://www.uoguelph.ca/~antoon/circ/sensor3.htm

I am abit of a newbie, can anybody explain to me what's going on here?

From what I understand, a small a/c voltage is sent out, and taken back
on another probe, which is then rectified and 'compared' to a reference
level which energises the relay. Which bits of the cct do what
parts/how they do it, I'm not sure about.

I need to be able to alter this circuit by taking the logical state(0
or 1) of the sensor output, and combining it with a few other gates
before then driving the output relay.

I'm always bad at understanding transistors, and CMOS outputs. Why
does he use PNP rather than NPN here? Does it matter? Can I use say
BC107's (which I have at home) instead?

Regards,
Mark

Hi, Mark. Tony Van Roon's circuit uses 2/4ths of a 4093, which is a
quad 2-input NAND gate with Schmitt trigger. The gate shown as N1 is
set up as a cheapie oscillator, and outputs a square wave (0V - 12V) at
a frequency of a couple of KHz. This signal is AC coupled through the
caps C1, C2 and the liquid (which is assumed to have a relatively low
resistance) to the second part of the circuit. It's then half-wave
rectified and level-shifted by diodes D2 and D3 so as to charge up
capacitor C4. If the cap goes up to more than 60% or so of the power
supply (that would be around 7.5 to 8V in the diagram), that will send
N2 low. According to the diagram that will turn on the transistor T1,
which will turn on the relay.

First off, there's a conceptual problem here, which you'd find out as
soon as you tried to use this thing. I'm assuming your beer vat is
going to have foam. If the liquid is conductive (I believe beer is),
then the foam will be, too. Your basic idea, I believe, was sensing
fluid level, not foam level. Also, foam sticking on the electrodes may
cause the resistive path to remain unless you have them far enough
apart. Something to think about, but depending on the electrodes you
use and their spacing, it might be OK.

Second, the circuit shown is somewhat deficient in a couple of areas.
A transistor is a current-driven device. When you try to drive the
base of a transistor with a voltage, the bulk resistance of the
transistor plus the output impedance of the logic gate _may_ be enough
to save the transistor, but you should never depend on it. While
you're at it, you should know that the relay load really should be
connected to the collector rather than the emitter. Second, resetting
the logic gate by opening up the GND connection is an invitation for
all sorts of bad things to happen, as the cap tries to discharge
through other pins of the IC.

Here's another try that avoids these problems (view in fixed font or
Notepad):

` VCC VCC
` + +
` | |
` | C|
` Sensor 1N4002 - C|RY1
` ^ C|
` ^ ^ | |
` | | | |
` C| C| '----o
` --- --- |
` --- --- __ __ |
` ___ | | .--| | .--| | ___ |/
` .-----|___|--o o->|-o---o---o---| |&H|o-| |&H|o-|___|-o-| Q
` | | | C| | | '--|__| '--|__| R | |>
` | __ | - --- .-. .-. .-. |
` | .--| | | ^ --- | | | | R| | |
` o--| |&H|o--o | | | | | | | | |
` | '--|__| | | '-' '-' '-' |
` | === === | |22 ohm | |
` C| GND GND === | === ==` --- GND o | GND GND
` --- |=|
` | o |
` === |Reset
` GND |
` ==` GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Everything above is the same as Tony's circuit, except as shown. The
cheesy reset was replaced with a 22 ohm resistor in series with a
switch to discharge the cap. That should take care of resetting the
relay circuit if you need it. Second, Tony's circuit has an active low
logic output driving a PNP transistor. By using one of the spare
inverters, you've got an active high signal which drives an NPN. The
last change is that you've got the relay load at the collector of the
transistor, and there's a series resistor R to the base of the
transistor along with a base ballasting resistor to make sure it's
really off.

You haven't mentioned what relay you're using, but I'll assume it's one
with a coil power of about 3/4 watt. For a 12V coil, that would mean
about 60 mA. It's customary, when using a small signal transistor as a
switch, to drive the base with a current of about 1/10th of the
collector current. If you set R so that the 4093 output is pushing
6mA, you'll be in the Groan Zone. That's too much current to pull from
a regular 4000-series CMOS output at 12V. But, it should be OK for two
CMOS outputs. So, you might want to try replacing the third gate with
this (view in fixed font or Notepad):

`
` VCC VCC
` + +
` | |
` 1N4002| C|
` - C|RY1
` ^ C|
` | |
` __ | |
` .--| | ___ '----o
` | |& |o-|___|--. |
` o--|__| 3.9K | |
` | | |/
`---o o---o-| Q
` | | | |>
` | __ | .-. |
` o--| | ___ | | | |
` | |& |o-|___|--' | | |
` '--|__| 3.9K '-' |
` 10K| |
` === ==` GND GND
`
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

This way, you've also finished all the 4093 gates on your IC, and found
a good use for each of them.

Good luck, and feel free to ask if you have any further questions.
Chris

 

[MarkMc]

Hi Chris

Thanks very much for taking the time to explain this for me, and offer
improvements.

I've printed off your message and ccts from notepad for a thorough
read.

If you can suggest a good electronics book which explains transisters
very well for beginners/noddy's, that would be great.

You may be right about the foam, but I'm hoping to build the U/back and
hop back in such a way that I get minimal foaming - hopefully I can
achieve this.??

For my cct, I need to drive the relay from two sensors - a high and low
water mark, and I'd like to provide both a reset and an override ("just
turn the pump on") feature. Furthermore, I'd like to be able to use
the same cct and switch between the underback sensors and the hop back
sensors (DPDT switch?). It may be that I'll need two separate sensor
ccts for this, as each may need to be calibrated separately. Dunno.

Any suggestions you have here would be very welcome! I did draw up a
truth table for the kind of logic I think I need, here
http://www.mcgee-family.com/projects/BreweryDesign/brewery_overview.htm
(go to the bottom of the page for the table).

This means that I need an assortment of AND, OR and INVERTER gates. I
know each of these can be built from NAND gates (IIRC OR gate made from
3 NAND's), but this is a bit messy. Any suggested improvements here
would be very welcome too!

I forgot to include schmitt triggers on some of the switched inputs, so
I guess a schmitt NAND like the cct above or a dedicated schmitt
trigger is in order here?

Cheers,
Mark

 

[MarkMc]

Oh, btw Chris, the relay I was planning on using was model YX97F from
Maplin electronics. Technical info for this is very thin on the ground
indeed, but IIRC, the coil has an impedence of about 330 ohms.

I calculate this to mean 36mA through collector of transistor, and
using your 10th rule for base current, this gives 3.6mA.

Would this mean I can just use a single NPN (I have BC107B's at home)
or is this still too much for the poor blighter? (sorry, I don't have
the spec sheets in front of me to check, but it still sounds high for a
signal transistor).

Perhaps a Darlington pair would be better for driving the relay here?

Cheers,
Mark

 

[Chris]

MarkMc wrote:

Hi Chris


Thanks very much for taking the time to explain this for me, and offer
improvements.


I've printed off your message and ccts from notepad for a thorough
read.


If you can suggest a good electronics book which explains transisters
very well for beginners/noddy's, that would be great.


You may be right about the foam, but I'm hoping to build the U/back and
hop back in such a way that I get minimal foaming - hopefully I can
achieve this.??


For my cct, I need to drive the relay from two sensors - a high and low
water mark, and I'd like to provide both a reset and an override ("just
turn the pump on") feature. Furthermore, I'd like to be able to use
the same cct and switch between the underback sensors and the hop back
sensors (DPDT switch?). It may be that I'll need two separate sensor
ccts for this, as each may need to be calibrated separately. Dunno.


Any suggestions you have here would be very welcome! I did draw up a
truth table for the kind of logic I think I need, here
http://www.mcgee-family.com/pr­ojects/BreweryDesign/brewery_o­verview..htm
(go to the bottom of the page for the table).


This means that I need an assortment of AND, OR and INVERTER gates. I
know each of these can be built from NAND gates (IIRC OR gate made from
3 NAND's), but this is a bit messy. Any suggested improvements here
would be very welcome too!


I forgot to include schmitt triggers on some of the switched inputs, so
I guess a schmitt NAND like the cct above or a dedicated schmitt
trigger is in order here?


Cheers,
Mark



Oh, btw Chris, the relay I was planning on using was model YX97F from
Maplin electronics. Technical info for this is very thin on the ground
indeed, but IIRC, the coil has an impedence of about 330 ohms.

I calculate this to mean 36mA through collector of transistor, and
using your 10th rule for base current, this gives 3.6mA.

Would this mean I can just use a single NPN (I have BC107B's at home)
or is this still too much for the poor blighter? (sorry, I don't have
the spec sheets in front of me to check, but it still sounds high for a
signal transistor).

Perhaps a Darlington pair would be better for driving the relay here?

Cheers,
Mark

Hi, Mark. Sorry about the delay in response. Busy with other things
over the weekend.

Your project looks like it's well though out, with a lot of time and
sufficient money having been invested. Boy, you're serious about beer.
Good job.

Your truth table seems to describe the function of a drain pump. Turn
on when H and L are ON, and don't turn off until H and L are OFF. This
action is described as a SET-RESET (SR) latch, which is a type of
flip-flop (FF). Again, you can see how using one of the Gems floats
with hysteresis would make things much simpler here. Many of their
sensors can be set so the microswitch or hall effect switch will not go
on until the float reaches a higher position, and then will stay on
until the float reaches the lower position. This hysteresis would
simplify things quite a bit. And I would personally really recommend
you use something that's made for the application. If you asked me to
do the electronics for this, I'd select a Gems switch (actually two --
you'll want one for overflow check, too), and see if I could do what
you needed with the float switch contacts and another switch or two.
But there it is. Let's see what we can do with logic gates,
transistors and relays.

Before anything else, you should know your transistor should be OK for
switching a 12VDC 36mA relay coil. Your BC107B is a small signal
amplifier transistor with a Vceo of 50V (how high a voltage it can
handle), an Ic(max) of 100mA (maximum collector current) and a minimum
Hfe (DC current gain) of 200. This is good news, because the "rule of
10" actually says that if you're switching a given collector current
load, you should inject 10X the current suggested by the DC current
gain. Or, if you like, the equation:

Ib = Ic / (Hfe /10)

That would mean you need a base current of 36 mA / (200 / 10) = 1.8 mA.
That's good news because a 4000-series CMOS gate won't have a problem
sourcing or sinking 1.8 mA with a power supply of 12VDC.

Now let's take a look at the circuit requirements. You've gone beyond
what you can do with a "one chip solution", unless you were to use a
PIC or BASIC Stamp. So let's splurge and use a 555 for your oscillator
signal (you're going to need those gates for other things).

`Beer Oscillator
`
` VCC VCC VCC
` + + + Osc Out
` | | | ^
` .-. .---o-----o---. |
` | |68K | 8 4 | |
` | | | | ---
` '-' | | ---
` | | | |
` o-------o7 | |
` | | 3o---------'
` .-. | |
` | |10K | 555 |
` | | .---o6 |
` '-' | | |
` | | | |
` o---o---o2 |
` | | |
` --- | |
` --- | 1 5 |
` |.01uF '---o-----o---'
` | |
` === ==` GND GND
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

This oscillator should be good for driving almost an infinite number of
your 4093 sensors at somewhere near the same frequency as your 4093
oscillator. Just remember that you have to keep both the oscillator
signal and the sensors disconnected from earth ground or any other
potential. This is called a "floating" signal. ;-)

Let's review the bidding on these sensors. Now, both the high and the
low stainless probes are going to have one of these on the receiving
side like you talked about before:

` Beer Sensor
` H (or L) Probe`
`
` ^
` |
` ---
` --- __
` C | .---| |
` o---->|-o----o--o |&H|o---> H (or L)
` | D | | '---|__|
` - --- .-. 1/4 4093
` D ^ --- | |
` | C| | |15 Meg
` | | '-'
` | | |
` === === ==` GND GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

OK. Now, we have two 12V logic signals that go active low when they
sense liquid level. We're getting there. Let's be creative and call
these signals H and L.

Time for a little diversion here. Look at this little trick:

` The Dreaded NOR RS Flip Flop
` __
` R o-------|>=| .-------------------.
` |1 |o-o----o Q | S | R | Q | Q' |
` .----|__| | | | | | |
` | | | 0 | 0 | No Change |
` | | | | | | |
` | .--------' | 0 | 1 | 0 | 1 |
` | | | | | | |
` '----------. | 1 | 0 | 1 | 0 |
` | __ | | | | | |
` '--|>=| | | 1 | 1 | 0 | 0 | (disallowed)
` |1 |o-o----o Q' | | | | |
` S o--------|__| '-------------------'
`created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You can hook up a couple of NOR gates (CD4001) and feed their outputs
back into their inputs to do this trick. We can use this to get your
flip flop action, because you want the RS FF to SET when H is low and L
is low, and you want the RS FF to RESET when H is high and L is high.
Here's how:

` Beer Flip Flop VCCVCC
` + +
` | |
` __ - C|
` .--| | ^ C|
` H >--o-o |& |o--. | C|
` | '--|__| | | |
` | | '--o
` | | __ |
` | '---|>=| "R" __ |
` | |1o|o-----|>=| ___ |/
` | .---|__| |1 |o-o--|___|- -| BC107B
` | | .----|__| | 6.8K | |>
` | | | | .-. |
` | | | | | | |
` | | | .--------' 10K| | |
` | | | | '-' |
` | | '----------. | |
` | | | __ | === ==` | | __ '--|>=| | GND GND
` '-----------|---|>=| |1 |o-o
` | |1 |o-----|__|
` .-----------|---|__| "S"
` | __ |
` | .--| | |
` L >--o-o |& |o--'
` '--|__|
`created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You can see from the diagram that the "S" input only goes high when H
and L are low, and the "R" input to the FF only goes high when H and L
are high. (Note: logic ICs have power connections which were not
included here. Pin 14 is +12V and pin 7 is GND for both the 4001 and
4093.)

You can get your Override/Reset action by putting a switch in with the
relay above like this:


` VCC VCC
` + +
` | |
` | |
` - C|
` ^ C|
` | C|
` | | Override
` | | _/
` '----o---o/ o--.
` | |
` | |
` | |
` |/ |
` >-| |
` |> |
` | |
` | |
` === ==` GND GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

There's a lot more you can do with this stuff, but it's a little
tedious in ASCII art. This should give you a start. Feel free to
email me if you have any questions. And you might want to wait a day
or so before building -- there are several really good electronics
people in this ng who may spot an error in the above or have a better
idea.

By the way, also feel free to let us know how you're doing.

Good luck
Chris

 

[MarkMc]

Hi Chris

Yes, I do seem to take beer very seriously! The quality of it at
least!

Thanks very much for such a detailed response. I really appreciate you
taking the time to explain this stuff to me. All that you say makes
sense.

I may have missed this, but I assume I need to have a 'common' probe,
and then the H & L probes?

Hey, the ovverride switch is very neat - so simple, why didn't I think
of that! - got carried away with the logic gates I guess! No need
for a resistor here at all?

I actually need to control/pump/empty two seperate vessels (not at once
- they share the pump). How would you suggest I switch between one set
of sensors and another? Two identical circuits, but switch the final
pump drive from an OR gate or switch between one cct or another in to
the relay coil?

btw, I did look at the commercial float switches and considered them a
bit pricey (maybe you have a good diy source?). Not sure what's
involved with using these things - are they just simple switches?

It's not likely I'll get to build the cct in the next few days anyway -
work is rather busy at the moment - working weekends etc.

Thanks again
Cheers,
Mark

 

[Chris]

MarkMc wrote:

Hi Chris

Yes, I do seem to take beer very seriously! The quality of it at
least!

Thanks very much for such a detailed response. I really appreciate you
taking the time to explain this stuff to me. All that you say makes
sense.

I may have missed this, but I assume I need to have a 'common' probe,
and then the H & L probes?

Hey, the ovverride switch is very neat - so simple, why didn't I think
of that! - got carried away with the logic gates I guess! No need
for a resistor here at all?

I actually need to control/pump/empty two seperate vessels (not at once
- they share the pump). How would you suggest I switch between one set
of sensors and another? Two identical circuits, but switch the final
pump drive from an OR gate or switch between one cct or another in to
the relay coil?

btw, I did look at the commercial float switches and considered them a
bit pricey (maybe you have a good diy source?). Not sure what's
involved with using these things - are they just simple switches?

It's not likely I'll get to build the cct in the next few days anyway -
work is rather busy at the moment - working weekends etc.

Thanks again
Cheers,
Mark

Yes, Mark, you will actually need three electrical connections for each
tank -- H, L, and common. The current flows through the OSC. output
into the H and L inputs, charging up the caps to change the logic
state. If you've got a metal tank or have a metal drain, it may be
easier to attach the oscillator output to that rather than have a third
probe for each tank.

The bypass/override switch acts in the exact same way as the transistor
switch in parallel with it -- they both provide a very low impedance
path to GND when ON. It won't hurt the transistor at all to wire a
switch in parallel with it, because of the protection diode across the
relay coil. The inductive kick caused by the relay turning off will be
recirculated by the diode, whether the switch or transistor turned off.

If you had two pumps as well as two vessels, you might want to just use
a 4P3T switch to transfer control from one to another. But you only
have one pump for two vessels. If the one you're not using is always
empty, you can just run the two sets of sensors in parallel (H or L
will go active if either one of the sensors is making continuity). But
if you're using both vats at once, make the oscillator common go to
both vats, and just use a DPDT switch to switch between H and L sensor
inputs. This is very low frequency stuff (2KHz signal) so you don't
have to worry about frequency effects at all.

`
` Vat 1
`
` .---------------o-------> Upper Probe
` |
` o---'
` H o----o--__ .------------o-------> Lower Probe
` o------|---.
` | |
` | | .----o-------> Common
` | | |
` | | |
` o------' | |
` L o----o--__ | |
` o------. | |
` | | | Vat 2
` | | |
` | '---|----o-------> Upper Probe
` | |
` Osc o--------. | |
` | '-------|----o-------> Lower Probe
` | |
` | |
` '--------------o----o-------> Common
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


If you go with this, you may want to figure out some way to ensure that
the pump valve and the switch are going in the right direction. Either
that or you can rely on your Bavarian sense of Teutonic thoroughness to
make sure every time. ;-)

Float switches are a bit pricey. But "in for a penny, in for a pound".
When I contract test or automation jobs, I try to reach an
accomodation with the customer. The goal, as always, is to provide the
right balance between function, reliability and total customer cost.
It's the customer's business, money and goals, so the decision about
how to proceed and what to spend is always the customer's decision.

Looking at the great job you've done on the rest of the project, and
the obvious investment in money, time, and intelligence, I would assume
the most reliable solution would be more important to the customer than
lowest cost. I believe that would be float level sensors, even though
they're more expensive. But this resistive probe option seems like
fun, and if you construct it well, it should be reliable (especially if
you have an external safety in case of electronics failure). This is a
hobby, and it's about the journey as well as the destination, right? I
think this modification to the circuit you found on the net is fairly
straightforward, and should work well if constructed properly.

Be sure to put the electronics in an enclosure which will resist
splashing. Take the time to label everything, especially connectors
and switches. Also, make sure you document your circuit and keep the
documentation with your equipment. You'll be able to get help if
you've got a problem then, and you won't have to remember what you did
several months or years later if there's a glitch.

Good luck and Cheers,
Chris

 

[MarkMc]

Hi Chris

I'm planning on using some small stainless steel vessels for the
'tanks' - only about 1-2 litres capacity required for each. The Will
have a metal drain, so I'll try to find a way of attaching the OSC to
this.

I was thinking about using two switches - one for manual/automatic and
another for on/off for the pump in manual mode. I assume I can just
interject these in to the collector of the relay driver transistor? I
assume switch noise isn't an issue when energising the relay?

With regards to the re-use of the pump: The brewery setup is going to
have quite a few plumbing valves, so these will be set to the required
settings before firing up the electronics. Of course, with so many
valves to worry about (see http://tinyurl.com/bljgl), I am a bit
concerned that I'll get them wrong sometimes, so what I plan to do is
print off a couple of lookup sheets and laminate them to keep them nice
and dry, which tells me what setting each valve should be in for each
stage of my process. Brewing is a fairly timeconsuming and slow-moving
process, so it shoouldn't be difficult to make sure everything is setup
ok, especially with a checklist. It's when things start going wrong
that it gets a bit lively!


Re "in for a penny" - given no wife/family, I'd agree, but I've spent
"most of the budget" on the actual brewing equipment, so the luxury
stuff (like this control stuff), needs to be done on a budget, but hey
it's fun to do this stuff, and it's much more to talk about and show
off to your friends!

If I find I have problems with the sensors 'sensing' foam and such
like, then I'll have to re-think (the time delay will help with
spending more, I'm sure! )

Actually, I'll be needing to update this hardware to include a heater
in one of the vessels (the underback). I was thinking I could use a
temperature controller (FE33L - Maplin, has LCD display etc - cool),
but I only want the heater to come on when the temp controller says
"too cool" (fine, theres a signal from FE33L for this @1.5v), *AND*
when the pump is on. This part I'm not 100% sure about, because the
auto/manual + on/off switching complicates things a bit.

Any suggestion on how to do this? (obviously another relay+transistor
etc) I assume some kind of AND gate with pump signal and temp ctrl?

Cheers,
Mark

 

[Fred Stevens]

I seem to remember that there are optical level sensors that work for
liquids that are not transparent. They give an electrical signal as an
output which you can trigger on.

Fred.

 

[Chris]

MarkMc wrote:

Hi Chris

I'm planning on using some small stainless steel vessels for the
'tanks' - only about 1-2 litres capacity required for each. The Will
have a metal drain, so I'll try to find a way of attaching the OSC to
this.

I was thinking about using two switches - one for manual/automatic and
another for on/off for the pump in manual mode. I assume I can just
interject these in to the collector of the relay driver transistor? I
assume switch noise isn't an issue when energising the relay?

With regards to the re-use of the pump: The brewery setup is going to
have quite a few plumbing valves, so these will be set to the required
settings before firing up the electronics. Of course, with so many
valves to worry about (see http://tinyurl.com/bljgl), I am a bit
concerned that I'll get them wrong sometimes, so what I plan to do is
print off a couple of lookup sheets and laminate them to keep them nice
and dry, which tells me what setting each valve should be in for each
stage of my process. Brewing is a fairly timeconsuming and slow-moving
process, so it shoouldn't be difficult to make sure everything is setup
ok, especially with a checklist. It's when things start going wrong
that it gets a bit lively!


Re "in for a penny" - given no wife/family, I'd agree, but I've spent
"most of the budget" on the actual brewing equipment, so the luxury
stuff (like this control stuff), needs to be done on a budget, but hey
it's fun to do this stuff, and it's much more to talk about and show
off to your friends!

If I find I have problems with the sensors 'sensing' foam and such
like, then I'll have to re-think (the time delay will help with
spending more, I'm sure! )

Actually, I'll be needing to update this hardware to include a heater
in one of the vessels (the underback). I was thinking I could use a
temperature controller (FE33L - Maplin, has LCD display etc - cool),
but I only want the heater to come on when the temp controller says
"too cool" (fine, theres a signal from FE33L for this @1.5v), *AND*
when the pump is on. This part I'm not 100% sure about, because the
auto/manual + on/off switching complicates things a bit.

Any suggestion on how to do this? (obviously another relay+transistor
etc) I assume some kind of AND gate with pump signal and temp ctrl?

Cheers,
Mark

Hi, Mark. Apart from just turning off the power, you can use a 3-way
SPDT switch (ON-OFF-ON) to give you both the pump OFF and pump OVERRIDE
functions like this:

`
` VCCVCC
` + +
` | |
` - C|
` ^ C|
` | C|
` | |
` '--o
` |
` Logic | Override
` o | o
` | |
` ___ |/ Pump |
` -|___|-o-| Off ==` | |> GND
` .-. |
` | | |
` | | ==` '-' GND
` |
` |
` ==` GND
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

The switch actually has three positions -- up, middle, and down. In
the middle position the switch pole isn't connected to either throw.
That makes it an ideal, relatively easy hardware solution.

When you have any kind of low voltage high input impedance sequential
logic, static from machine operators and moving parts and electrical
noise can be a PITA, changing logic states and damaging ICs. Actually,
as the prices of PLCs (Programmable Logic Controllers) came down to
reality in the early 1990s, I basically stopped doing any factory
industrial control circuits with 4000-series CMOS just for that reason.
PLCs generally have optoisolated inputs and RC filters on the inputs
to reduce the chance of electrical noise or ESD getting through. And
again, this is another good reason for using a float. It's not
affected by any of this stuff. But there are ways to deal with EMI/RFI
in CMOS circuits...

First, you obviously wouldn't have any chance at all if the FF inputs
were just hanging out in the breeze. But the caps and the schmitt
trigger inputs condition the "real world" inputs and will effectively
prevent electrical noise from affecting them (assuming you're using
good caps and your circuit layout has a good low impedance ground
path). Noise might affect the FF itself, though.

In order to minimize the risk of that occurring, you can do several
things. The first and most important thing is to try to prevent the
inductive kick of the pump switching off from creating a big spark that
will cause EMI. To do that, you should place a snubber across the
load. For AC loads (you are using an AC pump, right?), you should use
an R-C snubber across the load.

`
` ||
` .-------||----o------o------.
` | || | | |
` | RY | | .-. |
` | .-./ R| | |Pump
`240VAC _ | / | | C|
` / \ MOV |/| '-' C|
` ( ~ ) / | | C|
` \_/ /'-' C | |
` | | | --- |
` | | --- |
` | | | |
` '-------------o------o------'
`
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You want to choose an R based on the maximum switching current of your
relay. Let's say you've got 240VAC, a 5 amp relay contact, and a 1/2
amp pump. You then want a value for R which will bring the current
fairly close to the rated current. If you use 100 ohms, that will get
you to about 3 A switching current. You can then choose a value for C
(line-rated cap, of course) which will just keep the relay contacts
from arcing. For relays with clear cases, you can actually watch the
arc disappear as you increase the value of C. For enclosed relays, you
should remove the cover to check. You didn't mention pump current, but
I'll guess it's rated for less than half an amp. For that sized pump,
I would start with 0.1uF and see what happens. Among my trove of
delightful stuff I've got a small box of different sized Quencharcs to
just plug in and see what works. But it seems ITW/Paktron is having
difficulty with getting distributors for their product these days, so
you'll have to use discrete parts. Try the Cornell-Dubilier MMP6P1K
(0.1uF, 600V, self-healing polyester film, you can get this from
Farnell if you reference Newark P/N 95F7892) and a 100 ohm 1 watt or
greater resistor.

Unless you've got a particularly large pump, this should do the job.
To make it just about the perfect snubber, put a 280VAC rated MOV
across the R-C snubber (the bigger the better - physical size on MOVs
is proportional to joule rating). That will prevent the voltage across
the cap from exceeding the rated voltage on the inductive kick, which
will basically mean the snubber will last forever. It's preferrable to
put the snubber/MOV across the load, but if that's not practical, you
can put it across the relay contacts.

Having reduced or eliminated the relay spark, it's still better to put
the relay physically as far away from the logic circuit as practical.
The worst thing you can do is use a PC mount relay, and put the relay
right next to the FF IC (don't laugh -- I did it once long ago). To
quote from the wisdom of '70s vintage Sesame Street, "The Solution...
To Pollution... Is Dilution". If you've got a source of EMI/RFI
pollution, the farther away it is, the lesser effect, the better. It
might even help to mount the relays for the control logic in another
enclosure next to the pump, and have low voltage control lines going
from the controller box to the relay box.

On the IC side, there's a few things you can do. Bypass the Vcc pin of
each IC with an 0.1uF ceramic cap to GND. Keep the wires of the FF as
short as possible, by using two NORs on one side of the IC and using
direct wiring there.

Between working on the relay (EMI source) and the IC (EMI target), you
should be in pretty good shape. Experiment around a little here once
you've constructed this. Try switching two pumps if you have them, and
see if this affects things. If you don't have two pumps, try putting a
greater load on the pump (momentarily lock the rotor or put a friction
load on) and see if the increased noise causes the logic circuit to
upset. This isn't a proof that your solution works, but it helps to
give confidence in the work you've done. The fact is, a hobbyist
doesn't have the tools to really solve this kind of problem, so the
best you can do is build up a lot of protection, test it as best you
can under real world conditions, and then hope for the best. But with
only one FF on one IC with no inputs extending from the immediate area,
you shouldn't have much to worry about after you do the above stuff.

Your little controller board (amazingly, only 10 pounds!) seems to have
a logic level output for heating. Again, you can use relay logic to
make sure the heater is on only when the pump is on like this:

`
` || ||
` .-------||----o------o------o------||------.
` | || | | | || |
` | CRY1 | | .-. | CRY2 |
` | .-./ R| | |Pump |
`240VAC _ | / | | C| .-.
` / \ MOV |/| '-' C| Heater| |
` ( ~ ) / | | C| | |
` \_/ /'-' C | | '-'
` | | | --- | |
` | | --- | |
` | | | | |
` '-------------o------o------o--------------'
`
`
` VCC VCC
` + +
` | |
` - C|
` ^ C| RY2
` | C|
` | |
` '---o
` |
` LO from ___ |/
` FE33L >-|___|-o-|
` | |>
` .-. |
` | | |
` | | ==` '-' GND
` |
` ==` GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

The .pdf file referenced on the Maplin page doesn't say much about the
sensor itself. You have to be careful about installing it in a food
service environment, though. This requires some looking into. Another
issue might be that the module will have a "bang-bang" output, which
means that it turns on the heater when the temp is too high, and turns
off when it's too low. There's no proportioning of the output, which
might cause pretty major oscillation in liquid temperature -- in fact,
it might make it worse than not having any controller at all. If you
adjust so the water starts at a certain initial temperature, it may be
better to control the temperature of the liquid by just using a lamp
dimmer in series with the heater, replacing CRY2 directly in the
circuit above, and keeping it at a setting that will keep the
temperature fairly stable. You can then use the FE33L as a temp
display only. Don't know. Could use some more information here. Or
even better, one or two good experiments with tap water before you brew
anything.

Hmmn. Home brewry vs. wife -- a difficult choice. I'd have to think
'er over a while. ;-)

Cheers!
Chris

 

[MarkMc]

Hi Chris

Thanks once again for a very detailed response. I really do appreciate
you giving me your time on this.

In response to your post.

Thanks for the insights regarding EMI. I was aware of the EMI produced
by the pump, and I managed to buy a joined 100R resistor and (can't
remember) I think 0.1uF capacitor rated at 400v in one package,
specifically for the purpose of protecting relay contacts. Hopefully
these will be ok.

I'm not sure what current rating the pump is, but it's afairly hefty
s/s cellar pump. I bought it reconditioned, but the home brew shop I
bought it from said that I should fit a 5A fuse. The pump is indeed
A/C, 240v. I'm going to buy a controller from RS to control the flow
rate, so I think this fits in series with the pump load IIRC.

Of course, the heater, pump 'logic' is a perfect solution, as is your
suggestion of a 3-way switch for the on/off/override requirement - such
simplicity! I have about 14 years experience in my job (computer
programmer), and one of the first things I try to teach inexperienced
guys is "simple is best".

You use the short-hand "FF", but I can't see for the life of me what
this is refering to! Can you explain?

Also, I have no idea what a MOV is, can explain what this does?

Following your advice, I'll place the 240v stuff and relays in one
metal enclosure, and mount this as far away as possible from the 12v
logic stuff, which I'll obviously place in a separate enclosure - I
assume metal will be best for this too?

I amazingly knew to put a bypass cap from VCC to gnd to help with
voltage fluctuations, but thanks again for the professional advice.

Regarding the FE33L, I already have one of these, but the documentation
is pretty poor. The 'probe' that can be bought to fit the device is
soldered (by the user-i.e. me) on the the board, so I was wondering if
I could make a food safe probe of my own by fitting the wires to a
piece of stainless steel rod?

I've been planning on testing this thing in the lab before using it in
anger with water and beer from a can. I assume I'm best to include a
preset resistor in the sensor ccts, and make any adjustments by
adjusting this?

Thanks once again for the help.

Cheers!
Mark

 

[Chris]

MarkMc wrote:

Hi Chris

Thanks once again for a very detailed response. I really do appreciate
you giving me your time on this.

In response to your post.

Thanks for the insights regarding EMI. I was aware of the EMI produced
by the pump, and I managed to buy a joined 100R resistor and (can't
remember) I think 0.1uF capacitor rated at 400v in one package,
specifically for the purpose of protecting relay contacts. Hopefully
these will be ok.

I'm not sure what current rating the pump is, but it's afairly hefty
s/s cellar pump. I bought it reconditioned, but the home brew shop I
bought it from said that I should fit a 5A fuse. The pump is indeed
A/C, 240v. I'm going to buy a controller from RS to control the flow
rate, so I think this fits in series with the pump load IIRC.

Of course, the heater, pump 'logic' is a perfect solution, as is your
suggestion of a 3-way switch for the on/off/override requirement - such
simplicity! I have about 14 years experience in my job (computer
programmer), and one of the first things I try to teach inexperienced
guys is "simple is best".

You use the short-hand "FF", but I can't see for the life of me what
this is refering to! Can you explain?

Also, I have no idea what a MOV is, can explain what this does?

Following your advice, I'll place the 240v stuff and relays in one
metal enclosure, and mount this as far away as possible from the 12v
logic stuff, which I'll obviously place in a separate enclosure - I
assume metal will be best for this too?

I amazingly knew to put a bypass cap from VCC to gnd to help with
voltage fluctuations, but thanks again for the professional advice.

Regarding the FE33L, I already have one of these, but the documentation
is pretty poor. The 'probe' that can be bought to fit the device is
soldered (by the user-i.e. me) on the the board, so I was wondering if
I could make a food safe probe of my own by fitting the wires to a
piece of stainless steel rod?

I've been planning on testing this thing in the lab before using it in
anger with water and beer from a can. I assume I'm best to include a
preset resistor in the sensor ccts, and make any adjustments by
adjusting this?

Thanks once again for the help.

Cheers!
Mark

Welcome back, Mark. This type of conversation should be of some use to
a lot of beginners in electronics.

Your pump is a lot beefier than I had guessed. Your snubber of 100
ohms + 0.1uF may help some, but if you remove the cover from the relay
and watch it switch off, you'll still get an arc. It might be best to
move the relay physically to another enclosure if you have problems
with electrical noise.

We mentioned in an earlier post that "FF" is shorthand in electronics
for Flip-Flop, the basic memory storage unit in electronics. It holds
1 bit of information, and can be a logic 0 or 1. The RS (Set-Reset,
and don't ask why it's always called RS instead of SR, I don't know) FF
is the most basic one that can be cobbled together, with only two logic
gates. You can use NOR or NAND gates to make one. They operate a
little differently from each other, but that's another story. You've
got a NOR RS FF in your control circuit.

An MOV is a Metal Oxide Varistor, a device developed by the wizards at
General Electric Semiconductor during the early '60s, when men were men
and women were glad of it. An MOV is a device that doesn't conduct at
all until its in its breakover region. At that point, it conducts and
acts something like a bidirectional zener. It's commonly used as
device protection across the line. The problem is that the crystalline
structure of the zinc oxide breaks down when it absorbs energy, so they
can be destroyed instantly if there's no series impedance to limit the
current in the event of a line voltage surge. An MOV is a wear part,
and should be replaced occasionally.

Since you've got a 400V cap, you want an MOV that will conduct before
the voltage across the cap gets to that voltage. The bigger the MOV
the better, but you might want to look at Maplin HW13P Suppressor
250VAC 308 in Stock Ł0.69. Here's a reference which starts in on an
explanation of the MOV:

http://www.currenttechnology.com/paper_5.htm
http://www.currenttechnology.com/paper_6.htm

GE wrote the bible, an applications manual on MOVs, but I don't think
it's available online.

For your application, just put your snubber across the relay contacts,
and put the MOV in parallel with the snubber, and you should be OK.

Using a metal enclosure for both boxes should be OK. Be sure that, if
you've got line voltage in a metal box, you make sure to earth the
chassis as well as fusing as necessary. Use a GFCI is mandatory where
water and line voltage are in proximity. Make sure that, even if the
box drops on the floor, there won't be loose wires with line voltage in
the box. You also might want to get someone knowledgeable to take a
look at your work before you plug it in.

Your probe might be a bit of a problem, as we mentioned before.
Anything used in a food service application should be able to be washed
down and sterilized. The probe shown in the .pdf article doesn't look
like it will fill the bill. If you have a description of the sensor
and/or part number (is it an LM35?), I might be able to give you more
help.

The .pdf article on the FE33L is somewhat descriptive, but it isn't a
data sheet and it doesn't have a schematic of the controller itself.
Possibly if you have a better reference, I might be able to give you a
hand.

* Heater Wattage?
* FE33L additional documentation?
* Sensor type? (If it looks like a TO-92 transistor, you could just
copy down the numbers)

I'm looking forward to seeing your work in progress on your website.

Cheers!
Chris

 

[MarkMc]

Hi Chris

FF - yes of course, just didn't twig! Obviously, too much home brew
has killed some brain cells!

Thanks for the info about the MOV, I've heard of varistors, but never
knew what they were.

The relay is a tiny (ultra miniature they call it) PCB mount thing.
I'm not sure if the cover is removable. I can vandalise one as part of
'research' I suppose!

The .pdf file on the Maplin site is new - it wasn't there when I bough
my unit a few months ago. Would've been useful. I've been developing
a cct for temperature control using a PIC microcontroller which
interfaces to the FE33L, and spits out an RS232 signal for a PC to read
- I'm using the FE33 mainly as a tempsensor and LCD display - all of
which I'd probably implement using discrete components for version 2
now I've learned a bit about PIC's.

I did have a .pdf file of the manual for FE33L, but I can't find it (a
USB memory stick got trashed), otherwise I'd stick it on the web site.
If I get time, perhaps I can scan in the paper version. It's very low
on detail though, and certainly isn't a datasheet and doesn't have a
schematic. It basically has two outputs for temperature control - too
hot or too cold, so you can control a heat and cool source.

By the way, the relay (YX97 - maplin) is rated to 10A

The temperature probe is the FE34M, and I have one of them. I wouldn't
want to put it in hot wort. Hence I'd like to make something from s/s
if that's at all possible.

I just looked through my Maplin order history, and I see that I ordered
RG23 500v 0.1uF capacitors, and also RG22Y Contact Suppressor 100R and
0.1uF in series 250v max.

Using your suggested 'relay logic' setup, would I need to put two
suppressors in the cct, one across each, or can I still stick with your
original suggestion of having these across the load? Any reason for
your change here?

The heat source will be controlled by RS#655-622, as will the pump.
Well, that's the intention anyway. But I am yet to decide on what to
use for the heat source. I haven't yet found my s/s containers for
this application, so the size will dictate the heat source to a certain
degree.

I was thinking about using an electric kettle element 2kW or similar.
I will be needing to heat about 25L of liquid from ~50C to 65C, fairly
rapidly, while recirculating with the pump.

Sorry Chris, what is GFCI?

I'm getting an old coal shed converted to use as the brewery, and it'll
have it's own consumer unit, earth rod and RCD main switch...

Cheers,
Mark

 

[Chris]

MarkMc wrote:

Hi Chris

FF - yes of course, just didn't twig! Obviously, too much home brew
has killed some brain cells!

Thanks for the info about the MOV, I've heard of varistors, but never
knew what they were.

The relay is a tiny (ultra miniature they call it) PCB mount thing.
I'm not sure if the cover is removable. I can vandalise one as part of
'research' I suppose!

The .pdf file on the Maplin site is new - it wasn't there when I bough
my unit a few months ago. Would've been useful. I've been developing
a cct for temperature control using a PIC microcontroller which
interfaces to the FE33L, and spits out an RS232 signal for a PC to read
- I'm using the FE33 mainly as a tempsensor and LCD display - all of
which I'd probably implement using discrete components for version 2
now I've learned a bit about PIC's.

I did have a .pdf file of the manual for FE33L, but I can't find it (a
USB memory stick got trashed), otherwise I'd stick it on the web site.
If I get time, perhaps I can scan in the paper version. It's very low
on detail though, and certainly isn't a datasheet and doesn't have a
schematic. It basically has two outputs for temperature control - too
hot or too cold, so you can control a heat and cool source.

By the way, the relay (YX97 - maplin) is rated to 10A

The temperature probe is the FE34M, and I have one of them. I wouldn't
want to put it in hot wort. Hence I'd like to make something from s/s
if that's at all possible.

I just looked through my Maplin order history, and I see that I ordered
RG23 500v 0.1uF capacitors, and also RG22Y Contact Suppressor 100R and
0.1uF in series 250v max.

Using your suggested 'relay logic' setup, would I need to put two
suppressors in the cct, one across each, or can I still stick with your
original suggestion of having these across the load? Any reason for
your change here?

The heat source will be controlled by RS#655-622, as will the pump.
Well, that's the intention anyway. But I am yet to decide on what to
use for the heat source. I haven't yet found my s/s containers for
this application, so the size will dictate the heat source to a certain
degree.

I was thinking about using an electric kettle element 2kW or similar.
I will be needing to heat about 25L of liquid from ~50C to 65C, fairly
rapidly, while recirculating with the pump.

Sorry Chris, what is GFCI?

I'm getting an old coal shed converted to use as the brewery, and it'll
have it's own consumer unit, earth rod and RCD main switch...

Cheers,
Mark

Hello again. The folks at Maplin were kind enough to email an
attachment with more information on the FE33L temperature module. If
you want, you can have them forward it to you also.

The use of this module for real temp control looks iffy, but you might
get barely passable results with the British can-do spirit and a little
luck. Unfortunately, bacteria also have that spirit of derring-do, and
your FE34 sensor probably won't cut it. By putting it in a s/s sheath,
you'll probably be doing a good job of insulating it from the liquid.
That will slow down your temperature response big-time, which is
probably a fatal flaw.

All is not lost, though. They've probably got a commercial thermistor
(temperature-variable resistor) as the temp sensor, and it's more than
likely a standard value. There's no schematic in the .pdf, but I'd
guess they're probably asserting a logic high on a pin, and then
measuring current through the sensor with a series resistor. Either
that, or they're doing an R-C charging thing like the POT instruction
with the BASIC Stamp. It might be possible for you to measure the
thermistor resistance at room temperature, then measure again at a
higher set temperature to get a handle on its temperature coefficient
(delta ohms per degree). Or call Maplin and ask nicely (although I'm
not sure they'd be interested in undercutting their market for their
1.99 GBP sensors). It's probably a standard value, and also probably
available as a purchase part from some vendor somewhere. If you're
really lucky, it might be a value you can get by cannibalizing a
digital thermometer. As another possibility, you might be able to
purchase a bead thermistor, and affix it to the inside of a thin sealed
s/s tube with thermally conductive epoxy, but this sounds a little
doubtful. I'm the most uneasy about creating a situation where we
contaminate the brew. That can get people sick -- not a good thing. A
final possibility might be affixing the bead thermistor to the outside
of the tank. If it's copper or brass, it's a great conductor of heat.
If you blanket the air side, and use thermally conductive epoxy to
affix the thermistor to the outer wall, you might not even have to put
anything inside the vat. I like that option best.

The FE33.pdf from Maplin shows how to interface the 1.5V logic from the
temp control module to transistors and relays. I'd definitely watch
your current drive here. If you've got 0.8V across a 10K resistor,
you're only squirting 80 microamps into the base of the transistor.
That isn't going to be enough, realistically, to drive a decent sized
relay. You could use it to drive a solid state relay, or if you're
still going to use a large relay to drive your heaters, you might use
the first transistor to drive another one, which then drives the relay
like this (view in fixed font or M$ Notepad):


12V
+
|
.-. 12V
22K| | +
| | |
'-' |
| ___ |<
o-|___|--| PNP
| 8.2K |\
| |
1.5V ___ |/ .---o
LOW o-|___|-o-| NPN | |
Signal 10K | |> | C|
.-. | 1N4- C|RY2
| | | 002^ C|
10K| | === | |
'-' GND | |
| === == === GND GND
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de



But, having shown that you can do something, you should then ask
yourself whether it's smart. From what I've heard about brewing,
you'll have to be consistently within a couple of degrees if you want
things to work right. To be honest, you're not going to reliably get
that accuracy or repeatability with this setup. This setup won't work
well on a consistent basis. Even with a rock solid 1.5V supply, a
precision thermistor matched to the characteristics of the FE34,
controlled ambient temperature, and everything else optimized, I don't
think you're going to get better than +/-5 degrees C or so
repeatability. That's 60 to 70 degrees C, and the extremes will
probably ruin your batch. It might be better to think this one out,
and work on a control setup which will do justice to the rest of your
effort, time and money. In for a penny, in for a pound (GPB).

There's nothing wrong with manually turning on the heat and monitoring
with a thermometer, just like the Bavarians of yore. And if you want
to have some kind of automated temp controller, there are units
available on ebay which will do a much better job than this little
module. Control of temp to within 1 degree C or so is very possible.
You can then use a standard precision thermistor with your temp
controller (you might even be able to buy it with the controller) to do
the job.

By the way, a GFCI is a Ground Fault Circuit Interrupter, and it's a
requirement any time you're using line voltage in a wet place. In the
event that there's a ground fault, the GFCI will cut power to reduce
the risk of electrocution. If you're using electric heaters on a metal
vat with liquid inside, you have to use one of these.

Good luck. Take some time, and think 'er over.

Good luck
Chris

 

[MarkMc]

Hi Chris

I did once get the .pdf from Maplin that you refer to. It's just a
scan of the instructions which come with the module - assuming you have
the same file. Perhaps I'm learning some of this electronics lark as I
too came to the conclusion that I wouldn't be able to drive my relay
from the tiny current available from the module.

I assumed that a Darlington pair would help me out here. Is there any
reason why you suggest the NPN-PNP cct in particular?

The temperature control is definitely a luxury thing, and by the look
of things is best left until version 2 of this setup which is already
tring to achieve a lot.

The heating side of things I can see getting used in two ways -
1.) To perform stepped mashes - only for a tiny proportion of brews
(luxury)
2.) To keep the wort at a set temperature when recirculating - losses
may occur at the pump and in the pipework.

I have heard about homebrew systems existing called RIMS (RecIrculating
Mash System) and HERMS (HEated Recirculating Mash System), and they
rely recirculating the wort and for HERMS, heating it at the same time,
so it must be possible.

The pump will be pumping the liquid at all times when the heater is on,
so the liquid shouldn't be in contact with the heater element for any
length of time, so the liquid temperature level should be rising very
slowly and steadily with any luck, but perhaps you're right, manual
control and a normal glass thermometer may well be a better solution.
But it's not very geeky, is it!

There's two things which need to happen heat wise;
1). The heat of the liquid in the container must *never* go over 70-75C
(well, not for long) as enzymes in the wort, which are performing the
starch conversion of the grain, can de-nature and become useless for
the mash and render the brew unfermentable - not desirable! This limit
may be even lower (say 60C) at some stages for stepped mashing.
2). Heating and pumping/recirculating must stop when the temperature in
the mash tun (not the underback where we'll be heating the wort and
pumping from) is at the desired step temperature, say 66C

So thinking about it, an even more custom solution is required with not
one, but two temperature probes.

I was wondering - I have PIC microcontrollers 16F628A at home, with
necessary programming hardware and software development tools.

I could make something to perform a controlled level out to the heating
element, using the reference voltage generator of the 16F628A rather
than simply turning the heater on and off. Of course the problem here
is that I don't know how to scale up a 0-5v variable range to what's
required for the heater element running on mains voltage. i.e. do I
need to vary the current/resistance or the voltage peak-to-peak of the
heater element, I'm not sure how to achieve either.

Hmmm, maybe on/off is ok for the <= 70C part, but that still leaves me
wondering how to physically measure the temperature. I don't mind
making my own sensor out of stainless steel rod (somehow?) and
performing the calibration etc, and using a cct/PIC microcontroller to
act on the levels and perhaps drive an LCD display for the underback
and the mash tun.

From reading the FE33L manual, they suggest any probe will work as long
as it has a resistance < 30 ohms and that the shorter the wire, the

more accurate it will be. Any suggestions on making a probe form
stainless steel rod?

I take it a GFCI is different to an RCD? I was always planning on
using an RCD in the 240v cct.

Thanks once again,
Mark