Driver circuit. How do you figure out what transistor and re

O

obliquez

Guest
Hiya, i'm new to this group, so i have no idea where i should post this
thread. So hopefully im posting in the right place.

Anyway, my problem is, i've got to connect a temperature sensor to a
buzzer. Sounds simple? Not so, i've gotta use a driver circuit to
connect the components. The sensor uses TTL logic output, so a driver
circuit has to be used to connect it to the buzzer, which runs on a
3-24V input.

Frankly speaking, i have no idea what i'm supposed to do. I don't know
how to figure out the values of the resistor or what transistor to use
for the driver circuit. Can anyone please please enlighten me.

It's part of my final year project, so it's really important that i get
help asap. Will be utterly grateful to anyone who can provide some
help.

In case my summary is not very clear, what i need to know now is just,
what kinda driver circuit should i use? And what are the values of the
components, i.e resistor, transistor, that i have to use to get that
driver circuit.

Argh! I'm not explaining very well. I hope you guys know what i'm
trying to say

Please please help!
 
The sensor I'm using is a liquid level sensor.

http://content.honeywell.com/sensing/prodinfo/liquidlevel/100437-en.pdf#seahttp://content.honeywell.com/sensing/prodinfo/liquidlevel/100437-en.pdf#search='honeywell%20lle%20sensor'

I am supposed to connect it to a buzzer, I've got 2 coz i'm not sure
which is more suitable.

http://sg.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3921177&N=0

http://sg.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3921189&N=0

Basically, I'm supposed to incoporate these components into a
container. When liquid is poured in, up to a certain level, the sensor
will 'sense' it, and the buzzer is supposed to sound.

Is this enough information?

My teacher said that since the sensor uses TTL Logic, I can't connect
the buzzer directly to the sensor. I have to use a driver circuit. And
that's where my problem lies.

Thanks
 
I did attend classes, but for final year project, alot of information
are not in our syllabus. =( So i've gotta find it from other sources.

My teacher asked me to search the web instead. So that's why I'm here.

Anyway thanks, I need all the luck i can get.

Thank you John as well..

-smiles-
 
Jonathan Kirwan wrote:
On Tue, 21 Jun 2005 02:53:20 -0400, John Popelish <jpopelish@rica.net
wrote:

obliquez wrote:
The sensor I'm using is a liquid level sensor.

http://content.honeywell.com/sensing/prodinfo/liquidlevel/100437-en.pdf#seahttp://content.honeywell.com/sensing/prodinfo/liquidlevel/100437-en.pdf#search='honeywell%20lle%20sensor'

I am supposed to connect it to a buzzer, I've got 2 coz i'm not sure
which is more suitable.

http://sg.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3921177&N=0

http://sg.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=3921189&N=0

Basically, I'm supposed to incoporate these components into a
container. When liquid is poured in, up to a certain level, the sensor
will 'sense' it, and the buzzer is supposed to sound.

Is this enough information?

My teacher said that since the sensor uses TTL Logic, I can't connect
the buzzer directly to the sensor. I have to use a driver circuit. And
that's where my problem lies.

Thanks

I don't think you need any additional parts except a 9 volt battery.
The sensor can operate from any supply between 5 and 12 volts. It
outputs a logic high (the positive supply voltage) when in air and a
logic low (negative supply voltage) when submersed.

Interestingly, I came to a confused impression in reading the data
sheet on this part.

"When no liquid is present, light from the LED is internally reflected
from the dome to the photo-transistor. When liquid covers the dome,
the effective refractive index at the dome-liquid boundary changes,
allowing some light from the LED to escape. Thus the amount of light
received by the photo-transistor is reduced and the output switches,
indicating the presence of liquid."

Since the diagram shows the photo-transistor connected one side to
ground (so it pulls low harder when more light is presented to it) and
since the Schmidt trigger isn't shown as an inverter, I tended to
conclude that the input node to the Schmidt was lower when more light
was present (which is when there is no liquid presented to the surface
of the detector.) And that, thus, the output would be low, as well,
at this time.

However, two things confused me about this. One is that I know that
some data sheets don't get the exact details of the logic right in the
diagram (inverter vs non-inverting, for example) and the other is that
the data sheet does specify the "output sink current" but not the
"output source current," which suggests strongly to me just as you
say, above.

It wasn't until I went elsewhere on the web that I discovered that you
are exactly correct about the output.


They have 3
leads. The red lead connects to battery positive, the blue to battery
negative and the green is the output.

If your buzzers are self oscillating (they make a tone, not just a pop
when connected to a 9 volt battery, red lead to positive) then all you
need to do is connect the black lead to the sensor output and the red
lead to the battery positive. Either buzzer should draw less than the
output current rating of 10 mA with a 9 volt supply.

Several things mitigate against this solution, I think. Most
importantly, this is a project and is probably designed to _show_ some
modest proficiency. Not much, I fear. But at least some. Just
getting lucky by hooking up a buzzer device to an output described
this way,

"The output is intended as a TTL compatible output signal, for
interfacing to logic systems. For interfacing with other types of
circuitry an appropriate buffer circuit must be used."

...would probably be violating the spirit of the project.

I suppose, if being fractious about it, I could also point out that
the two buzzers specify a maximum of 8-10mA and the sensor specifies a
worst case (at 80 C) of 3mA sinking drive and that any design that
depends on the accident of these matching up might be "graded down" a
bit. Also, since the OP actually says, " I don't know how to figure
out the values of the resistor or what transistor to use for the
driver circuit," I tend to assume that this is what the teacher
intends to be used in the design.

(The buzzer also specifies a nominal 12V. I suppose it can run on 5V,
but I wonder if the purpose of this is to also get the OP to actually
do a reasonable solution using two supplies, one at 5V and one at 12V.
No idea there, and no big deal either way, but it is a question that
crosses my mind.)

Finally, _if this is an electronics degree program__, I have a hard
time understanding how such a simple interface escapes what I'd
imagine should have been the appropriate training and the acquired
knowledge in the "final year." The solution seems non-critical in
nearly every regard and I have a hard time understanding how they
haven't they discussed BJT transistors operated as simple switches. I
begin to wonder things like, "what year is the 'final' year?" and
"what is this degree actually in?" and "what school, for gosh sake?"

Jon
Click to expand...
Wow, I'm sorry, but i don't quite get it. Are you saying that i don't
need a buffer circuit? I can just connect the sensor directly to the
buzzer? Coz my teacher insists that i do need a driver circuit. Hence
all the questions.

I am not an undergrad. I'm not getting a degree. Where I'm from, we
have schools called Polytechinics (17-19 yr olds). So i'm not sure
what's it equivalent to in your country. =)
 
Erm, I'm using a 9V battery for testing. But in the final prototype, i
have to use those kinda flat batteries, like for watches?

So do i not need a driver circuit for this? But it is part of the
requirement of my project..

He says that since the sensor output is TTL logic, the buzzer cannot be
directly connected. A driver circuit must be used.

Thanks!
 
obliquez wrote:
I did attend classes, but for final year project, alot of information
are not in our syllabus. =( So i've gotta find it from other sources.

My teacher asked me to search the web instead. So that's why I'm here.

Anyway thanks, I need all the luck i can get.

Thank you John as well..

-smiles-
Click to expand...
Hi. The Honeywell LLE sensor has a built-in LED and phototransistor.
Both of them are pointed out towards the lens, which is mounted so as
to come in contact with a clear liquid. When liquid contacts the
surface, some of the LED light which normally would be reflected back
to the phototransistor escapes into the liquid. This is sensed by the
phototransistor, which turns on. The LLE sensor operates on a 5VDC
supply, and has an open collector schmitt trigger output which can sink
up to 10mA at 25 degrees C, and 3 mA at 80C.

The piezo beeper you've chosen has a self-oscillating circuit built in
(usually the tipoff is if the data sheet specifies a DC voltage vs.
current or sound output level). However, your piezo beeper is
specified as operating on 12VDC, which is a bit of a problem, unless
you happen to have both the +5 and +12VDC supplies handy. If I were
doing this, I'd use a 5VDC piezo beeper to save a lot of hassle. It's
always easier if you can use one power supply instead of two. But,
it's your project, and you know what's best. So...

Let's look at the driver and interface circuitry. I'm assuming you
want the beeper to go on when liquid comes in contact with the sensor
lens. That means you want something which will go ON when the sensor
output is sinking current. Since there's nothing in the datasheet
about the sensor output transistor being able to handle a higher
voltage than 5V (although many do), let's assume it can't. If you had
a spare inverting logic gate, you could do something like this (view in
fixed font or M$ Notepad):
`
` +12V
` +
` +5V +5V |
` + + / \
` | | (BZ1)
` Red| .-. \_/
` .---o---. | |10K |
` | | | | |
` | | '-' |
` | LLE | | |\ ___ |/
` | Sensoro--o--| >O--|___|- -| 2N3904
` | |Grn |/ 10K | |>
` | | .-. |
` | | 10K| | |
` '---o---' | | |
` Blue| '-' |
` | | |
` | === ==` === GND GND
` GND
`created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Note that a pullup resistor is required at the output of the sensor to
give you your +5V/0V logic levels. The output is active low -- that
is, it goes to 0V when the sensor is ON. You reverse that with the
inverter. The output of the inverter then sources about 1/2 mA of
current into the base of the NPN transistor, which then turns on to
sink the 10mA or so for the piezo buzzer. This should do the job for
you.

If you don't happen to have any inverter logic gates handy (note that a
NAND or NOR gate can work just as well here), you'll have to use
another transistor to provide that inverting action:
`
` +12V +12V
` | +
` +5V +5V .-. |
` + + | |10K / \
` | | | | (BZ1)
` Red| .-. '-' \_/
` .---o---. | |10K | |
` | | | | o--. |
` | | '-' | | |
` | LLE | | ___ |/ | |/
` | Sensoro--o-|___|-| '-----o-| 2N3904
` | |Grn 10K |> | |>
` | | | .-. |
` | | | 10K| | |
` '---o---' === | | |
` Blue| GND '-' |
` | | |
` | === ==` === GND GND
` GND
`created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

You can see that when the first transistor turns ON (base current is
coming from the pullup because your sensor is OFF), it steals the base
current from the second transistor, which means your piezo buzzer will
be off. When the sensor turns ON, it prevents base current from
getting into the first transistor, so the other transistor is turned on
by the other pullup.

This isn't elegant, but it will work for you. If you want to look at a
piezo buzzer that works on 5VDC (ferinstance Farnell P/N 3921130), you
can simplify things quite a bit:

` +5V +5V
` + +
` | |
` Red| .-. +5V
` .---o---. | |10K +
` | | | | |
` | | '-' |
` | LLE | | ___ |<
` | Sensoro--o-|___|--| 2N3906
` | |Grn 10K |\
` | | |
` | | |
` '---o---' |
` Blue| |
` | / \
` | (BZ1)
` === \_/
` GND |
` |
` ==` GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

When the LLE goes on, it pulls current from the PNP, which turns it ON.
That sends current through the buzzer.

Hope your project goes well. Feel free to post again if you have any
further problems.

Good luck
Chris
 
I'm using a Honeywell lle sensor. LLE 105000 (Type 5) Mounts on the
inside. I intend to integrate the sensor into the handle of a mug.

It is required for me to include a driver circuit in my design. That's
what my teacher said. I heard that i can purchase a 3-24V circuit board
and get the right components, then connect the sensor and buzzer to it?
As in i get the circuit board and the right transistor and resistors?

Oh my, I know it's supposed to be really simple to understand, but i'm
not a very good student. =(

Thanks you guys for helping me out! =)
 
Oh, thanks so much.. Frankly speaking, i don't really understand
everything you're saying but i get the gist of it. The circuits you
drew up for me, seems to be what my teacher is asking for. I will show
it to him tommorrow and see what he says.

If i can get this driver circuit part out of the way, i will have to go
on to the next part, which is to include a temperature sensor and a
tilt sensor.

So far, i can't find small enough sensors. The temp sensor is to sense
liquid temperatures. And the tilt sensor is supposed to deactivate the
liquid level sensor. So, when the mug is in a tilted position, even if
the liquid covers the lle sensor, the buzzer won't activate.

I think i'm very bad at explaining stuff. Let me try again.

What i am supposed to do, is to incoporate all these components in a
mug. Making it a smart mug.

The lle sensor, will go on when the liquid reaches a certain level.
Thus, will cause the buzzer to go on as well.

The tilt sensor is to deactivate the lle sensor, so that the buzzer
will not go on if the mug is in a tilted position. i.e, when it is
being washed, etc..

The temp sensor, if the liquid is too hot, the buzzer will sound. I'm
not clear about this, but i think i will need another buzzer for this.

I have yet to be able to find a suitably small temp and tilt sensor. I
thought i could use this for the temp sensor, but i can't find a
circuit diagram. Therefore, i can't tell if i can incoporate it into my
circuit.

http://tsdpl.com/MPT-PROBE.htm

Thanks to everyone for all your help! you are all very nice ppl -grinz-
 
I learned abit about BJTs in my 1st year, but i'm afraid i've forgotten
most, if not all of what i have learnt. Because it was only a small
little part of a chapter of one of my modules. Lol

I will try to get back some of my old books from my friend and see if i
can read up on BJTs again. Is that what i need to know about?

Since verything has to be intergrated into a mug, i think that i can
only squeeze in one supply voltage, And it has to be in the form of
those flat round batteries. Maybe i can connect 2 or 3 flat batteries
in series or parallel?

thanks
 
Ok, i will. Then i will only be able to get back to you tommorrow
night. It's almost 2p.m. here right now. I will go to school tommorrow
morning and test out the components.

=)
 
Jonathan Kirwan wrote:
On 21 Jun 2005 22:51:15 -0700, "obliquez" <obliquez@gmail.com> wrote:

I learned abit about BJTs in my 1st year, but i'm afraid i've forgotten
most, if not all of what i have learnt. Because it was only a small
little part of a chapter of one of my modules. Lol

I will try to get back some of my old books from my friend and see if i
can read up on BJTs again. Is that what i need to know about?

BJTs are "bipolar junction transistors" and are what is usually just
called a "transistor." However, they are often called BJTs in order
to differentiate them from other transistors, like JFETs and MOSFETs.
And yes, that's what you need to learn about.

Since verything has to be intergrated into a mug, i think that i can
only squeeze in one supply voltage, And it has to be in the form of
those flat round batteries. Maybe i can connect 2 or 3 flat batteries
in series or parallel?

This makes things tricky. Problem #1 is that your sensor is specified
at 5V +/- 5%. This means something between 4.75V and 5.25V. Not much
of a margin to work with, assuming that it will be battery chemistry
determining your voltage.

If you are talking about those lithium button batteries, they don't
provide much more than 1mA or so. And they are 3V, usually. So you'd
need two, but that would be too much voltage, anyway. Problems with
voltage and more problems with current delivery.

Not to mention that you will need to verify that your buzzer will work
at whatever single voltage you settle on.

I think this is going to be an issue you will need to put some thought
into and verify with your teacher. Are you _sure_ that you cannot use
an external supply? If it must be batteries, what has been used
before with success? How much space do you really have? Have you
made measurements of your volume and can you spell them out, here?

Jon
Click to expand...

Morning guys, I have not slept all night and it's 7:15 over here now.
*Yawns*

I will be going to school soon, to try and sort out all the information
you all have given me. I will do the testing of the components. Such as
connecting the sensor and buzzer directly to see if it's a tone or pop.

and will clarify with ya all as soon as i can. I'm sorry for my
ignorance in this subject and area. Please bear with me. My utmost
gratitude for helping.
 
If I were you, I would be searching through the thermistor section of
the catalog. Much cheaper and have lots bigger signal. They are not
linear, but for a threshold function, like this, that makes no difference.
Click to expand...
I have no idea what you are talking about. Linear? threshold function?
-sheepish grin-
 
John Popelish wrote:
obliquez wrote:
If I were you, I would be searching through the thermistor section of
the catalog. Much cheaper and have lots bigger signal. They are not
linear, but for a threshold function, like this, that makes no difference.


I have no idea what you are talking about. Linear? threshold function?
-sheepish grin-

If you wanted to measure the temperature and convert the signal to a
temperature reading with an analog to digital converter (turn voltage
into number) linearity like 1 millivolt per degree is very handy. If
you just want a threshold function, like knowing whether or not the
temperature is greater or lesser than some single value, (either the
temperature exceeds the specified threshold value or it doesn't) all
you need is stability and sensitivity. That is, it doesn't matter
much how distorted the signal is at temperatures way hotter or way
colder than the one you are concerned with, but it matters that you
can measure that one temperature reliably (stability) and clearly
distinguish that temperature from those slightly hotter or slightly
colder (large temperature sensitivity).

The platinum sensor you mentioned, earlier has wonderful stability and
linearity, but it has very low sensitivity. Knowing that a
temperature is on the high or low side of a threshold by a degree is
hard to accomplish with one of those. Measuring the temperature over
a span of hundred of degrees within a several degree accuracy (an
electronic thermometer) is a better use for one of those.

Thermistors have a very distorted response to temperature, but they
are stable and can produce a large signal change for a small
temperature change, so they are well suited to threshold functions.
In order to make a thermometer out of them, you have to correct for
the distortion (varying amount of signal per degree over large
temperature swings). What you described about the requirements of
this project sounds to me like a threshold function.
Click to expand...
Hmm.. does sound like threshold function to me as well.. Basically, i
just want a temp sensor that will ON when the liquid is too hot. Let's
say 60 degree celcius? (What's the usual temp for a hot drink that is
not too hot?)

So does that mean i sound search for a thermistor instead?

Btw, i have tested the buzzer. It gives off a tone, not a pop. So i
guess i can just follow what you guys suggested and use a PNP, with
resistors? Like this?


+5V +5V
` + +
` | |
` Red| .-. +5V
` .---o---. | |10K +
` | | | | |
` | | '-' |
` | LLE | | ___ |<
` | Sensoro--o-|___|--| 2N3906
` | |Grn 10K |\
` | | |
` | | |
` '---o---' |
` Blue| |
` | / \
` | (BZ1)
` === \_/
` GND |
` |
` ===
` GND

will that work?
 
John Popelish wrote:

I think it will. I also think the driver is not needed. Also, try it
without the 10k to the +5 rail. I think it is not needed. A better
place for it is from the base to the +5 supply.

You will have to alter this when you get to combining the three
functions (tilt, level and temperature with logic to operate the buzzer).
Click to expand...
Mr. Popelish is suggesting that you might not need a transistor after
all -- that the 10mA output drive might be enough at 5V to turn on the
beeper like fig. a). In fact, he's probably right -- it should work
reliably at room temperatures with the reduced beeper current at 5V.

` VCC
` +
` VCC | VCC
` + | + VCC VCC
` | / \ | + +
` | (BZ1) | | |
` .---o----. \_/ .---o----. .-. |
` | | | | | | | |
` | | | | | 10K | | |
` | | | | | '-' |
` | LLE | | | | ___ | |<
` | o----' | LLE o--|___|-o-| 2N3906
` | | | | 10K |\
` | | | | |
` | | | | |
` | | | | |
` '---o----' '---o----' |
` | | / \
` | | (Mic)
` === === \_/
` GND GND |
` |
` ==` GND
`
` a) b)
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

He's also suggesting that, if you do need or want a transistor (after
all, if the teacher is asking for it, you probably had better either do
it or have a very good reason why not), you should do something like
fig. b). He's correct, of course. The base ballasting resistor is
traditionally at the base. It reduces current required to turn the
traansistor ON, as well as providing a better incentive to the PNP to
stay OFF when the sensor isn't sinking current (tied to Vcc through a
10K resistance instead of 20K).

You really should take a deep breath, make a cup of tea, and spend 5 or
10 minutes with a sheet of paper and a pencil, and figure out exactly
what you need for this assignment before posting again. It's kind of
disappointing to have gotten through one issue, only to find there are
two more. A plain English description of what you want the circuit to
do, and what components you've gotten (if any) for the tilt sensor(s)
and temp sensor would be in order. If I had to do this, I would
seriously consider using an LM34 to provide an output voltage
proportional to temperature (10mV per degree), and then use a
comparator to control switching at the appropriate temp.

You've actually been quite lucky here -- most homework questions are
ignored for obvious reasons. I would guess you're almost there, but
you'll have to do at least a little more work to fully describe your
problem. I'm not aware that anyone on this NG can read minds.

Good luck
Chris
 
Jonathan Kirwan wrote:
Q3 on the diagram is really Q1. Just forgot to rename it on the
schematic before generating the ASCII. Oh, well!

Jon
Click to expand...
Much better use of resources. I like it. But I _think_ the OP is
going with a single supply, though. I'm actually hoping he'll spend a
few minutes and really nail down what he wants here -- we're all
running around trying to read his mind. ;-)

The output of your program is really interesting. I'm going to take a
look at it when I get some time. Like your web site, too.

Thanks
Chris
 
Jonathan Kirwan wrote:
On 24 Jun 2005 12:00:45 -0700, "Chris" <cfoley1064@yahoo.com> wrote:

The output of your program is really interesting. I'm going to take a
look at it when I get some time. Like your web site, too.

It's darned easy to use. However, it *is* a DOS box kind of thing.
No Windows stuff. So you have to use a command line to work it.
Other than that, it's easy.

The source code all fits into a single source file, so it's
uncomplicated to compile and link. It is designed for Microsoft's VC
1.52C, however. In any case, I don't recommend messing with that part
of it, unless you really *do* have some time to play.

However, you can add new symbols easily. Just edit the ASC.SYM file
in an ASCII editor. You can define each orientation for parts, but
you don't have to define all the orientations if you don't care about
unusual cases. It uses what it can find, doesn't use what it can't.
I've already added the more obvious discrete parts but it does NOT
handle LTSpice's .ASY files that define complex part shapes and pins
as I just haven't yet struggled to deal with those and the WINDOW
definitions in the .ASC files, yet. So some things work well, but
where it doesn't know what to do it just leaves that part blank.
Someday, I'll work harder at examining the ramifications of dealing
with the .ASY files in a general and useful way and then it be a lot
more broadly useful.

I *do* like the ability to work with simple, discrete schematics in
LTSpice, check them out, etc., and then spit them out in ASCII for the
.basics group, though. Seems a good fit and it cuts my time down, a
lot, when trying to verify what I say before I say it and then produce
an ASCII representation that accurately reflects what I tested.

To produce that last schematic, I just typed "ASC j.asc" and it
generated the output on the DOS screen. I then copied that with the
clipboard and pasted it into my post. Must like with Andy's system.

I'd love to have some feedback about it, so let me know if you do.

Thanks for the kind comments, too.

Jon
Click to expand...



Thank you guys so much for your help so far!

I'm sorry that i seem to be ignorant (which i am) and slow (that too)
and i don't quite understand all of which you guys are trying to
explain to me. I don't really describe my problems well either. so
thanks alot for your patience.

The reason why i laid out my problems in parts, is because i thought it
would be easier for me to solve one step at a time. I apologise for the
trouble i caused.

So i shall now try to summarize everything.

For my project, I am supposed to embed an LLE sensor which will sound a
buzzer when the liquid reaches that certain level in the mug. A temp
sensor, or thermistor, which will sound the buzzer (I think it's
another buzzer, my teacher did not clarify this with me) if the liquid
is too hot. And lastly, a tilt sensor, which will either 1. turn off
the LLE and temp sensor or 2. turn off the buzzer when the mug is in a
tilted position.

My 1st problem was not knowing how to get a suitable buffer/driver
circuit to connect the LLE sensor and buzzer. But from all your help, i
have decided to use the PNP with the 2 10k resistors. If that works
best.

Now i have to figure out how to connect everything together and make it
work as a single unit. I have yet to find a suitable temp
sensor/thermistor or tilt sensor.

Btw, I'm sorry not to have mentioned this, but i only noticed it
yesterday when i was testing the LLE sensor. The LLE sensor has 4
wires, not 3. REd, blue, green and black. What the heck is the black
one for? I hope this doesn't create another problem.

erm.. is this laying out of my problem better?

Lastly, what is an OP? Does it refer to me? If it does.. I'm a her not
a he. -smiles-

Thank you so so much!!
 
obliquez wrote:
Thank you guys so much for your help so far!

I'm sorry that i seem to be ignorant (which i am) and slow (that too)
and i don't quite understand all of which you guys are trying to
explain to me. I don't really describe my problems well either. so
thanks alot for your patience.

The reason why i laid out my problems in parts, is because i thought it
would be easier for me to solve one step at a time. I apologise for the
trouble i caused.

So i shall now try to summarize everything.

For my project, I am supposed to embed an LLE sensor which will sound a
buzzer when the liquid reaches that certain level in the mug. A temp
sensor, or thermistor, which will sound the buzzer (I think it's
another buzzer, my teacher did not clarify this with me) if the liquid
is too hot. And lastly, a tilt sensor, which will either 1. turn off
the LLE and temp sensor or 2. turn off the buzzer when the mug is in a
tilted position.

My 1st problem was not knowing how to get a suitable buffer/driver
circuit to connect the LLE sensor and buzzer. But from all your help, i
have decided to use the PNP with the 2 10k resistors. If that works
best.

Now i have to figure out how to connect everything together and make it
work as a single unit. I have yet to find a suitable temp
sensor/thermistor or tilt sensor.

Btw, I'm sorry not to have mentioned this, but i only noticed it
yesterday when i was testing the LLE sensor. The LLE sensor has 4
wires, not 3. REd, blue, green and black. What the heck is the black
one for? I hope this doesn't create another problem.

erm.. is this laying out of my problem better?

Lastly, what is an OP? Does it refer to me? If it does.. I'm a her not
a he. -smiles-

Thank you so so much!!
Click to expand...
Hello again. First off, you don't seem to have a Honeywell LLE sensor
after all. I believe they make six different models, all of which have
identical electrical circuits and only three wires. The differences
are solely in housing types for different applications.

I think you've got a Honeywell LL-type sensor, which accounts for the
four wires. They make nine different kinds of LL-type sensors, and I
believe all of them are electrically the same and have 4 wires. The
Honeywell datasheets are typically inscrutable, but the installation
guides are usually a bit better. I've never been happy with Honeywell
industrial documentation on anything they make, I'm afraid. Usually
that would be a killer, but they happen to make really good stuff, for
the most part. That makes up for it, and their distributors can
usually answer any questions eventually. Look at this:

http://content.honeywell.com/sensing/prodinfo/liquidlevel/installation/xp4025-1.pdf

It shows a device that operates on a 5VDC to 16VDC supply, and has an
internal voltage regulator. The functions of the four wires on the
LL-type sensors are as follows:

* Red Vcc (+5VDC to +16VDC)
* Blue 0VDC
* Green Schmitt Trigger Output (internal open-collector transistor
with an internal 10K pullup to Vcc)
* Black To internal LED (use series resistor to Vcc such that I(LED)
= 30mA nominal -- do not exceed 40 mA. I(f)(LED)(typ) = 1.2V

This is kind of a critical problem here. You have to know what you're
working with, unless you want to let the smoke out. However, if you do
have this sensor, your job is now easy:

` VCC VCC VCC
` + + +
` | | |
` .-. | |
` R1| | | .-. VCC
` | | Red| R2| | +
` '-' .----o-----. | | |
` | | | '-' |
` | Black| LL |Green ___ | |<
` '-------o Sensor o-----|___|--o----|2N3906
` | | R2 |\
` | | |
` '----o-----' |
` Blue| |
` | |
` === / \
` GND (BZ1)
` \_/
` |
` |
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

By the way, I believe but can't determine for sure if the output is
active-high or active-low. By that I mean whether the logic level is 1
(Vcc) or 0 (0V) when water is present in front of the sensor. In most
all sensors of this type, it's active-low, and the driver above works
for that (turns the buzzer on when the sensor output goes low).
However, if you want the reverse effect for some reason (buzzer ON when
sensor output is HIGH), or if I'm wrong in my assumption that the
output is active-low, the internal 10K pullup makes your driver circuit
the easiest yet:

` VCC VCC VCC
` + + +
` | | |
` .-. | / \
` R1| | | (BZ1)
` | | Red| \_/
` '-' .----o-----. |
` | | | |
` | Black| LL |Green |/
` '-------o Sensor o------| 2N3904
` | | |>
` | | |
` '----o-----' |
` Blue| ===
` | GND
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

The internal 10K pullup resistor means that when the sensor output is
high, it will source enough current into the base of the NPN transistor
so that it will turn on for a 10mA load quite well.

Since you're supposed to be pulling 30mA for the LEDs, I wouldn't think
a few coin cells would last that long. They're basically intended for
a load of a mA or so at best. You might do better with a 9V
"transistor" battery -- that's more along the lines of what's
considered a normal load for them. The 9V battery will also be cheaper
in the long run -- you can get a lot more power from one of these than
a couple of coin cells.

R1 is used to regulate LED current. The installation sheet suggests
120 ohms, 1/4 watt for a 5V supply. If you're using a 9V battery, you
should have a 270 ohm resistor (1/4 watt is acceptable, 1/2 watt is
preferred). If you've got a 12VDC supply, you should use a 390 ohm,
1/2 watt resistor. R2 (2 ea.) can be 10K, 1/4 watt for all values of
Vcc.

Now, most tilt switches are just normally open mechanical switches,
where either a metal ball or a blob of mercury will close a connection
if the device tilts. You can just connect the normally open switch
from the base to the emitter of the transistor for either of the
diagrams above. That way, when the tilt switch turns on, it will
prevent the transistor (and buzzer) from turning on. Simple. If your
tilt switch is normall closed (the contacts open when the device tilts)
you can either use it to interrupt the power supply to the LL sensor,
or interrupt the flow of current to the base of the transistor. That
works for either of the above diagrams, too. Again, simple.

From your control logic, I'm not sure you actually want the hot alarm
to be disabled when someone's about to scald their lips. So, all we
Click to expand...
have to do to complete this is determine what you're going to use as a
temperature sensor. Please post back and let us know what the teacher
suggests, or if you've already bought something.

I can say that sensing temp with a thermistor will require an EXACT
part number. Thermistor resistances are usually specified at room temp
(25C), and have an almost infinite number of different resistance value
vs. temp. graphs. If you have to use a thermistor, you will need to
make a current source to create a voltage across the thermistor
(usually just another transistor and a couple of resistors will
suffice), and an IC comparator to compare the voltage across the
thermistor with a contrived voltage which would represent overtemp. If
the thermistor voltage exceeds the setpoint, the comparator can turn on
and drive another small beeper directly.

As I said in an earlier post, it might be easier for a newbie to spring
for an LM34 IC, which works on 5V to 30VDC as a power supply, and
outputs 10mV per degree. You can then feed that voltage directly into
the comparator without worrying about thermistor curves. You may have
a bit of a problem in that the LM34 looks like a TO-92 transistor and
is not immersible (it will short out your power supply), so you might
have to glue the sensor to the bottom or outside of the cup. Actually,
you usually need to purchase special thermistors which are made with a
watertight sheath, allowing them to be immersed, too. Anyway, you need
to find this stuff out, and get back to us.

You're almost there. Get back to us with more information about
whether you've got an LL-type level sensor, and the type and specific
part number of the temp sensor you need.

Good luck
Chris
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top