555 timer circuit controlled by tempreture?...help please

Jan 24, 2009

Hi,
I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Could anyone explain the best way for me to do this.

Thank you.

John Fields · Jan 24, 2009

On Sat, 24 Jan 2009 03:36:25 -0800 (PST), tel1e@hotmail.com wrote:

Hi,
I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Could anyone explain the best way for me to do this.

---
Instead of a timer, could you use a circuit which would cycle the heater
on when it was below 15C and off when it got to 15C?

A thermostat, in other words.

JF

Jan 24, 2009

On 24 Jan, 13:04, John Fields <jfie...@austininstruments.com> wrote:

On Sat, 24 Jan 2009 03:36:25 -0800 (PST), te...@hotmail.com wrote:

Instead of a timer, could you use a circuit which would cycle the heater
on when it was below 15C and off when it got to 15C?

A thermostat, in other words.

JF - Hide quoted text -

- Show quoted text -

Hi,

The processor only needs to be heated by the heater to get it to
start ....once it's running the temprature doesn't seem to effect it,
so I only need the heater to operate once.

A thermostat would be good but the temperature sensor would have to be
on the processor / heater and there would have to be some sort of
control so that it only operated once.

Thanks.

Christopher · Jan 24, 2009

On Sat, 24 Jan 2009 03:36:25 -0800 (PST), tel1e@hotmail.com wrote:

I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Below is one of my favorite hobby websites.

$7.87 board & parts to add the temperature control.

http://www.electronics123.com/s.nl/it.A/id.2117/.f

Here is a 8 sec to 2.3 hr timer board & parts using a 555.

http://www.electronics123.com/s.nl/it.A/id.386/.f

or

0 to 10 sec timer

http://www.electronics123.com/s.nl/it.A/id.459/.f?sc=8&category=44

* * * *

Christopher

Temecula CA.USA
http://www.oldtemecula.com

Jan 24, 2009

On 24 Jan, 14:48, Christopher <christop...@NOSPAMoldtemecula.com>
wrote:

On Sat, 24 Jan 2009 03:36:25 -0800 (PST), te...@hotmail.com wrote:

Below is one of my favorite hobby websites.

$7.87 board & parts to add the temperature control.

http://www.electronics123.com/s.nl/it.A/id.2117/.f

Here is a 8 sec to 2.3 hr timer board & parts using a 555.

http://www.electronics123.com/s.nl/it.A/id.386/.f

or

0 to 10 sec timer

http://www.electronics123.com/s.nl/it.A/id.459/.f?sc=8&category=44

* * * *

Christopher

Temecula CA.USAhttp://www.oldtemecula.com
Hi,

I saw that thermostat kit a while back & the thought of using it did
cross my mind....suppose I could couple it to a timer circuit & I
would be there.

Cheers.

John Fields · Jan 24, 2009

On Sat, 24 Jan 2009 08:56:16 -0800 (PST), tel1e@hotmail.com wrote:

On 24 Jan, 14:48, Christopher <christop...@NOSPAMoldtemecula.com
wrote:
On Sat, 24 Jan 2009 03:36:25 -0800 (PST), te...@hotmail.com wrote:

Below is one of my favorite hobby websites.

$7.87 board & parts to add the temperature control.

http://www.electronics123.com/s.nl/it.A/id.2117/.f

Here is a 8 sec to 2.3 hr timer board & parts using a 555.

http://www.electronics123.com/s.nl/it.A/id.386/.f

or

0 to 10 sec timer

http://www.electronics123.com/s.nl/it.A/id.459/.f?sc=8&category=44

* * * *

Christopher

Temecula CA.USAhttp://www.oldtemecula.com
Hi,
I saw that thermostat kit a while back & the thought of using it did
cross my mind....suppose I could couple it to a timer circuit & I
would be there.

---
I you have a sensor which measures temperature, why do you need a timer?

That is, if you turn on the power to the heater and then turn it off
when the sensor reads 15C what's the timer doing for you?

JF

Jan 25, 2009

On 24 Jan, 20:28, John Fields <jfie...@austininstruments.com> wrote:

I you have a sensor which measures temperature, why do you need a timer?

That is, if you turn on the power to the heater and then turn it off
when the sensor reads 15C what's the timer doing for you?

JF - Hide quoted text -

- Show quoted text -

Hi John,

Well I havent got either at the moment Im just exploring
possibilities.

I was going to build a timer to feed the heater for 5 seconds which
seems to be as long as the heater needs to be on for before the
processor starts to work. but then I though if I could control it via
temperature it would be a lot better.
The timer would trip & start to feed the heater but then once the
temperature reached 15 degrees C it would cut out regardless of what
the timer was doingso the timing wasnt so critical this would be a
lot more accurate than the 5 second blast that gets the processor
working.as I dont know how hot the processor gets in 5 seconds it
could be 40 degrees or it could be 50 degrees I dont know!

Ideally what I need is a circuit that only kicks in if the temperature
of the processor is below 10 degrees C & only stays on until it
reaches15 degrees C..that would be great.

Thanks.

Jamie · Jan 25, 2009

tel1e@hotmail.com wrote:

Hi,
I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Could anyone explain the best way for me to do this.

Thank you.

Below is something you can look at..

This will come on for 5 secs and monitor temp.

Version 4
SHEET 1 880 680
WIRE -16 0 -96 0
WIRE 176 0 -16 0
WIRE 224 0 176 0
WIRE 464 0 224 0
WIRE -96 80 -96 0
WIRE 464 80 464 0
WIRE 224 96 224 0
WIRE -16 112 -16 80
WIRE 192 112 -16 112
WIRE 304 128 256 128
WIRE 400 128 384 128
WIRE -16 144 -16 112
WIRE 176 144 176 80
WIRE 176 144 144 144
WIRE 192 144 176 144
WIRE 176 160 176 144
WIRE 224 160 224 144
WIRE 64 176 64 144
WIRE -96 272 -96 160
WIRE -32 272 -96 272
WIRE -16 272 -16 224
WIRE -16 272 -32 272
WIRE 64 272 64 240
WIRE 64 272 -16 272
WIRE 176 272 176 240
WIRE 176 272 64 272
WIRE 224 272 224 160
WIRE 224 272 176 272
WIRE 464 272 464 256
WIRE 464 272 224 272
WIRE -32 304 -32 272
FLAG -32 304 0
SYMBOL voltage -96 64 R0
WINDOW 3 24 44 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12.0
SYMBOL Comparators\\LT1017 224 128 R0
SYMATTR InstName U1
SYMBOL res 160 144 R0
SYMATTR InstName R2
SYMATTR Value 1200
SYMBOL res 160 -16 R0
SYMATTR InstName R3
SYMATTR Value 1200
SYMBOL Misc\\xvaristor -32 -16 R0
SYMATTR InstName U2
SYMATTR Value 1010
SYMATTR Prefix R
SYMBOL res -32 128 R0
SYMATTR InstName R1
SYMATTR Value 1000
SYMBOL cap 48 176 R0
SYMATTR InstName C1
SYMATTR Value .001000
SYMBOL res 160 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 470
SYMBOL res 400 112 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 470
SYMBOL pnp 400 176 M180
SYMATTR InstName Q1
SYMBOL res 448 160 R0
SYMATTR InstName R6
SYMATTR Value 5.5
TEXT 80 328 Left 0 !.tran 0 5 0 5 startup
TEXT -80 -32 Left 0 ;U2 is a PTC resistor.
TEXT 480 256 Left 0 ;Heaters

http://webpages.charter.net/jamie_5"

Jan 25, 2009

On 25 Jan, 01:50, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

te...@hotmail.com wrote:
Hi,
I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Could anyone explain the best way for me to do this.

Thank you.

Below is something you can look at..
This will come on for 5 secs and monitor temp.

Version 4
SHEET 1 880 680
WIRE -16 0 -96 0
WIRE 176 0 -16 0
WIRE 224 0 176 0
WIRE 464 0 224 0
WIRE -96 80 -96 0
WIRE 464 80 464 0
WIRE 224 96 224 0
WIRE -16 112 -16 80
WIRE 192 112 -16 112
WIRE 304 128 256 128
WIRE 400 128 384 128
WIRE -16 144 -16 112
WIRE 176 144 176 80
WIRE 176 144 144 144
WIRE 192 144 176 144
WIRE 176 160 176 144
WIRE 224 160 224 144
WIRE 64 176 64 144
WIRE -96 272 -96 160
WIRE -32 272 -96 272
WIRE -16 272 -16 224
WIRE -16 272 -32 272
WIRE 64 272 64 240
WIRE 64 272 -16 272
WIRE 176 272 176 240
WIRE 176 272 64 272
WIRE 224 272 224 160
WIRE 224 272 176 272
WIRE 464 272 464 256
WIRE 464 272 224 272
WIRE -32 304 -32 272
FLAG -32 304 0
SYMBOL voltage -96 64 R0
WINDOW 3 24 44 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12.0
SYMBOL Comparators\\LT1017 224 128 R0
SYMATTR InstName U1
SYMBOL res 160 144 R0
SYMATTR InstName R2
SYMATTR Value 1200
SYMBOL res 160 -16 R0
SYMATTR InstName R3
SYMATTR Value 1200
SYMBOL Misc\\xvaristor -32 -16 R0
SYMATTR InstName U2
SYMATTR Value 1010
SYMATTR Prefix R
SYMBOL res -32 128 R0
SYMATTR InstName R1
SYMATTR Value 1000
SYMBOL cap 48 176 R0
SYMATTR InstName C1
SYMATTR Value .001000
SYMBOL res 160 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 470
SYMBOL res 400 112 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 470
SYMBOL pnp 400 176 M180
SYMATTR InstName Q1
SYMBOL res 448 160 R0
SYMATTR InstName R6
SYMATTR Value 5.5
TEXT 80 328 Left 0 !.tran 0 5 0 5 startup
TEXT -80 -32 Left 0 ;U2 is a PTC resistor.
TEXT 480 256 Left 0 ;Heaters

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Jamie all I can see is a big list ?

Jamie · Jan 25, 2009

tel1e@hotmail.com wrote:

On 25 Jan, 01:50, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

te...@hotmail.com wrote:

Hi,
I'm very new to electronics so please bare with me.

I'm after building a timer circuit that will operate from a 12 volt DC
supply, the timer will control a small heater that I have built from 6
x 33 ohm resistors.
This small heater is fixed to a processor that isn't very stable when
it gets cold. Anyway the processor works fine when it is warmed up a
little. The timer will only allow the heater to be on for approx 4 - 5
seconds.

I would however like to add extra control to the circuit with a device
to interrupt the timer when the temperature of the heater reaches
approx 15 degrees C.

Could anyone explain the best way for me to do this.

Thank you.

Below is something you can look at..
This will come on for 5 secs and monitor temp.

Version 4
SHEET 1 880 680
WIRE -16 0 -96 0
WIRE 176 0 -16 0
WIRE 224 0 176 0
WIRE 464 0 224 0
WIRE -96 80 -96 0
WIRE 464 80 464 0
WIRE 224 96 224 0
WIRE -16 112 -16 80
WIRE 192 112 -16 112
WIRE 304 128 256 128
WIRE 400 128 384 128
WIRE -16 144 -16 112
WIRE 176 144 176 80
WIRE 176 144 144 144
WIRE 192 144 176 144
WIRE 176 160 176 144
WIRE 224 160 224 144
WIRE 64 176 64 144
WIRE -96 272 -96 160
WIRE -32 272 -96 272
WIRE -16 272 -16 224
WIRE -16 272 -32 272
WIRE 64 272 64 240
WIRE 64 272 -16 272
WIRE 176 272 176 240
WIRE 176 272 64 272
WIRE 224 272 224 160
WIRE 224 272 176 272
WIRE 464 272 464 256
WIRE 464 272 224 272
WIRE -32 304 -32 272
FLAG -32 304 0
SYMBOL voltage -96 64 R0
WINDOW 3 24 44 Left 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12.0
SYMBOL Comparators\\LT1017 224 128 R0
SYMATTR InstName U1
SYMBOL res 160 144 R0
SYMATTR InstName R2
SYMATTR Value 1200
SYMBOL res 160 -16 R0
SYMATTR InstName R3
SYMATTR Value 1200
SYMBOL Misc\\xvaristor -32 -16 R0
SYMATTR InstName U2
SYMATTR Value 1010
SYMATTR Prefix R
SYMBOL res -32 128 R0
SYMATTR InstName R1
SYMATTR Value 1000
SYMBOL cap 48 176 R0
SYMATTR InstName C1
SYMATTR Value .001000
SYMBOL res 160 128 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 470
SYMBOL res 400 112 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R5
SYMATTR Value 470
SYMBOL pnp 400 176 M180
SYMATTR InstName Q1
SYMBOL res 448 160 R0
SYMATTR InstName R6
SYMATTR Value 5.5
TEXT 80 328 Left 0 !.tran 0 5 0 5 startup
TEXT -80 -32 Left 0 ;U2 is a PTC resistor.
TEXT 480 256 Left 0 ;Heaters

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Jamie all I can see is a big list ?

down load LTSpice.

copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"

Jan 25, 2009

On 25 Jan, 14:55, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

On 25 Jan, 01:50, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
down load LTSpice.
copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Hi
Ok Jamie I have done that (Thanks) & I can now see a circuit diagram.

I'm not sure what this is...is it a bespoke circuit for my needs?

Will this supply power to the heater until it reaches a determined
temperature (15 degrees C) ?

Sorry for all the questions but I'm lost with this stuff & really
don't understand.

Thanks.

Jamie · Jan 25, 2009

tel1e@hotmail.com wrote:

On 25 Jan, 14:55, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

On 25 Jan, 01:50, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

down load LTSpice.
copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Hi
Ok Jamie I have done that (Thanks) & I can now see a circuit diagram.

I'm not sure what this is...is it a bespoke circuit for my needs?

Will this supply power to the heater until it reaches a determined
temperature (15 degrees C) ?

Sorry for all the questions but I'm lost with this stuff & really
don't understand.

Thanks.

U2 is a PTC "Positive Temperature Coefficient" resistor.
you'll want that close to the heater resistors which is
assumed to be on the Uc chip?

The PTC will increase in value as the temperature raises.
You need to shop around for the PTC from mouser, Digikey etc..
they come in various values and spec'd differently. for example
many are rated at what's considered room temperature, (25C)/77F.

R1 can be recalculated to match the PTC you get so that the voltage
at the network (- input) is just above the voltage at the (+) input
of the comparator at 15C. For example, 6.2 volts at (-) input at 15C would
be ok. you must think of this in terms of a voltage divider.

C1 and R4 is part of the timer, the two select the time and depth
of the threshold on the time cycle. You could actually omit these two
components from the circuit if all you want is a temperature switch.

If it's very cold, the PTC will most likely prevent the timer from
turning off the heaters until the PTC registers heat from the heater
resisters. If the temp is near the 15C, then the heaters will come on
and then off during the 5 sec window. As the initial temperature is
higher the timer will expire sooner, until at which point, the initial
temperature will be high enough to where the (-) input of the comparator
will be lower than the initial starting voltage at the (+) input, which
is calculated via the C1 and R4 and thus never turned on.

Q1, is a PNP power transistor. it must be large enough to handle
a 2 Amp load which shouldn't be a problem to locate..

The comparator used here, need not be the LTxxxx type here, you can
use others in place of it.
LM393 for example.
http://i2c2p.twibright.com/datasheet/LM193.pdf

You could even use an old LM741 to drive it. It really does not
matter in this circuit...

http://webpages.charter.net/jamie_5"

John Fields · Jan 26, 2009

On Sat, 24 Jan 2009 16:20:35 -0800 (PST), tel1e@hotmail.com wrote:

On 24 Jan, 20:28, John Fields <jfie...@austininstruments.com> wrote:
I you have a sensor which measures temperature, why do you need a timer?

That is, if you turn on the power to the heater and then turn it off
when the sensor reads 15C what's the timer doing for you?

JF - Hide quoted text -

- Show quoted text -

Hi John,

Well I havent got either at the moment Im just exploring
possibilities.

I was going to build a timer to feed the heater for 5 seconds which
seems to be as long as the heater needs to be on for before the
processor starts to work. but then I though if I could control it via
temperature it would be a lot better.
The timer would trip & start to feed the heater but then once the
temperature reached 15 degrees C it would cut out regardless of what
the timer was doingso the timing wasnt so critical this would be a
lot more accurate than the 5 second blast that gets the processor
working.as I dont know how hot the processor gets in 5 seconds it
could be 40 degrees or it could be 50 degrees I dont know!

Ideally what I need is a circuit that only kicks in if the temperature
of the processor is below 10 degrees C & only stays on until it
reaches15 degrees C..that would be great.

---
One of the problems with circuits of this type is that the time lag of
the sensor will allow the temp of the device being heated to rise to
higher than the desired temp. As long as you don't overheat the device,
(or the heater) though, you should be OK.

One thing that troubles me is that your processor is unstable when it's
cold.

I don't think it should be, so it may be a problem with something
external, like the crystal you're using.

Which processor are you using and what's its clock source?

In any case here's a circuit which will do what you asked for:

(View in Courier)

+12V>--+--------+----------+----+-------------+-------+
| | | | | |
RTH1 | | | | | |
[15130] [30k] | [100k] [560] [5.5]
| | | | | |
| | +----|----|--[<1N4148]--|-------+
| | | | | | |
+-[100k]-|-----+---|+\ | E |
| | | | >--+--[1k]-----B 2N3906 |
| [10k]<--|---|-/U1A C |
| | | | LM393 | C
| | [0.1ľF] | +-----B
| | | | ZTX1048A E
[15k] [30k] | +--|+\ |
| | | | | >--+ |
| | | +--|-/U1B| |
| | | | | |
GND>---+--------+-----+----+--------+-----------------+

The thermistor is a Measurement Specialties 44006RC:

http://www.meas-spec.com/product/t_product.aspx?id=4062

and here's the LTspice circuit list so you can play around with it:

Version 4
SHEET 1 880 680
WIRE -560 -160 -704 -160
WIRE -320 -160 -560 -160
WIRE 0 -160 -320 -160
WIRE 80 -160 0 -160
WIRE 304 -160 80 -160
WIRE 464 -160 304 -160
WIRE -320 -144 -320 -160
WIRE 448 -112 416 -112
WIRE 528 -112 480 -112
WIRE -576 -96 -608 -96
WIRE -448 -96 -544 -96
WIRE 80 -96 80 -160
WIRE 304 -96 304 -160
WIRE 464 -96 464 -160
WIRE -560 -80 -560 -160
WIRE -336 -16 -384 -16
WIRE -224 -16 -304 -16
WIRE -320 0 -320 -64
WIRE 416 0 416 -112
WIRE 448 0 416 0
WIRE 528 0 528 -112
WIRE 528 0 480 0
WIRE -608 16 -608 -96
WIRE -576 16 -608 16
WIRE -448 16 -448 -96
WIRE -448 16 -544 16
WIRE 144 48 -96 48
WIRE 464 48 464 -16
WIRE 464 48 208 48
WIRE 304 96 304 -16
WIRE -224 112 -224 -16
WIRE 0 112 0 -160
WIRE -320 128 -320 80
WIRE -32 128 -320 128
WIRE -384 144 -384 -16
WIRE 80 144 80 -16
WIRE 80 144 32 144
WIRE 128 144 80 144
WIRE 240 144 208 144
WIRE 464 144 464 48
WIRE -560 160 -560 0
WIRE -528 160 -560 160
WIRE -160 160 -448 160
WIRE -96 160 -96 48
WIRE -96 160 -160 160
WIRE -32 160 -96 160
WIRE -320 192 -320 128
WIRE 400 192 304 192
WIRE -160 256 -160 160
WIRE -704 272 -704 -160
WIRE -560 272 -560 160
WIRE -384 288 -384 176
WIRE -336 288 -384 288
WIRE -224 288 -224 176
WIRE -224 288 -304 288
WIRE -320 336 -320 272
WIRE -704 432 -704 352
WIRE -560 432 -560 352
WIRE -560 432 -704 432
WIRE -320 432 -320 416
WIRE -320 432 -560 432
WIRE -160 432 -160 320
WIRE -160 432 -320 432
WIRE 0 432 0 176
WIRE 0 432 -160 432
WIRE 464 432 464 240
WIRE 464 432 0 432
WIRE -704 496 -704 432
FLAG -704 496 0
SYMBOL npn 400 144 R0
WINDOW 0 89 36 Left 0
SYMATTR InstName Q1
SYMATTR Value ZTX1048A
SYMBOL res 448 -112 R0
SYMATTR InstName R1
SYMATTR Value 5.5
SYMBOL voltage -704 256 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 24 104 Invisible 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 12 .001 .001)
SYMBOL res -336 320 R0
WINDOW 3 36 67 Left 0
SYMATTR InstName R3
SYMATTR Value 30k
SYMBOL res -576 256 R0
WINDOW 3 38 70 Left 0
SYMATTR InstName R4
SYMATTR Value 15k
SYMBOL res -336 -160 R0
WINDOW 3 40 67 Left 0
SYMATTR InstName R6
SYMATTR Value 30k
SYMBOL res -336 -16 R0
SYMATTR InstName R7
SYMATTR Value 5100
SYMBOL res -336 176 R0
SYMATTR InstName R8
SYMATTR Value 4900
SYMBOL res 288 -112 R0
SYMATTR InstName R2
SYMATTR Value 560
SYMBOL Comparators\\LT1017 0 144 R0
WINDOW 0 -42 66 Left 0
WINDOW 3 -87 98 Left 0
SYMATTR InstName U1
SYMBOL pnp 240 192 M180
WINDOW 0 85 62 Left 0
WINDOW 3 56 34 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 224 128 R90
WINDOW 0 67 59 VBottom 0
WINDOW 3 67 62 VTop 0
SYMATTR InstName R9
SYMATTR Value 1k
SYMBOL diode 208 32 R90
WINDOW 0 -41 29 VBottom 0
WINDOW 3 -33 30 VTop 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL res -432 144 R90
WINDOW 0 -29 56 VBottom 0
WINDOW 3 -28 59 VTop 0
SYMATTR InstName R10
SYMATTR Value 100k
SYMBOL res -576 -96 R0
WINDOW 0 49 44 Left 0
SYMATTR InstName R5
SYMATTR Value 15130
SYMBOL cap -176 256 R0
WINDOW 0 42 34 Left 0
SYMATTR InstName C1
SYMATTR Value 0.1ľF
SYMBOL res 64 -112 R0
WINDOW 0 -44 36 Left 0
WINDOW 3 -47 66 Left 0
SYMATTR InstName R11
SYMATTR Value 100k
TEXT -696 464 Left 0 !.tran 10
TEXT -216 0 Left 0 ;10K POT
TEXT 376 -136 Left 0 ;HEATER
TEXT -552 -120 Left 0 ;YSI 44006

JF

Rich Grise · Jan 26, 2009

On Sat, 24 Jan 2009 06:04:08 -0800, tel1e wrote:

On 24 Jan, 13:04, John Fields <jfie...@austininstruments.com> wrote:
On Sat, 24 Jan 2009 03:36:25 -0800 (PST), te...@hotmail.com wrote:

Instead of a timer, could you use a circuit which would cycle the heater
on when it was below 15C and off when it got to 15C?

A thermostat, in other words.

The processor only needs to be heated by the heater to get it to
start ....once it's running the temprature doesn't seem to effect it,
so I only need the heater to operate once.

A thermostat would be good but the temperature sensor would have to be
on the processor / heater and there would have to be some sort of
control so that it only operated once.

Just design the heater to give the right "starting temperature" when

it runs "at full throttle", do your powerup sequence, and have the
processor turn it off during initialization.

Good Luck!
Rich

Jamie · Jan 27, 2009

tel1e@hotmail.com wrote:

On 25 Jan, 17:21, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

te...@hotmail.com wrote:

On 25 Jan, 14:55, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

On 25 Jan, 01:50, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

down load LTSpice.
copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Hi
Ok Jamie I have done that (Thanks) & I can now see a circuit diagram.

I'm not sure what this is...is it a bespoke circuit for my needs?

Will this supply power to the heater until it reaches a determined
temperature (15 degrees C) ?

Sorry for all the questions but I'm lost with this stuff & really
don't understand.

Thanks.

U2 is a PTC "Positive Temperature Coefficient" resistor.
you'll want that close to the heater resistors which is
assumed to be on the Uc chip?

The PTC will increase in value as the temperature raises.
You need to shop around for the PTC from mouser, Digikey etc..
they come in various values and spec'd differently. for example
many are rated at what's considered room temperature, (25C)/77F.

R1 can be recalculated to match the PTC you get so that the voltage
at the network (- input) is just above the voltage at the (+) input
of the comparator at 15C. For example, 6.2 volts at (-) input at 15C would
be ok. you must think of this in terms of a voltage divider.

C1 and R4 is part of the timer, the two select the time and depth
of the threshold on the time cycle. You could actually omit these two
components from the circuit if all you want is a temperature switch.

If it's very cold, the PTC will most likely prevent the timer from
turning off the heaters until the PTC registers heat from the heater
resisters. If the temp is near the 15C, then the heaters will come on
and then off during the 5 sec window. As the initial temperature is
higher the timer will expire sooner, until at which point, the initial
temperature will be high enough to where the (-) input of the comparator
will be lower than the initial starting voltage at the (+) input, which
is calculated via the C1 and R4 and thus never turned on.

Q1, is a PNP power transistor. it must be large enough to handle
a 2 Amp load which shouldn't be a problem to locate..

The comparator used here, need not be the LTxxxx type here, you can
use others in place of it.
LM393 for example.http://i2c2p.twibright.com/datasheet/LM193.pdf

You could even use an old LM741 to drive it. It really does not
matter in this circuit...

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Jamie thank you for your help, it's very appreciated.

Yes the heater SMD resistors are fixed to the top of the processor...I
plan to bond the PTC directly to the heater.

I noticed when looking up PTC resistors (Thermistor's) that some of
them have quite a high (30 seconds) TTC (Thermal Time Constant) will
this matter?

Do I need to get the lowest TTC I can find as from what I understand
this is the time that the Thermistor takes to react...is that correct?

Would a surface mount Thermistor be ok to use as this would be able to
bonded to the back of the heater quite easily...for some reason the
TTC isn't listed with the SMD versions I have seen.

Would you care to point me to the type I require...

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=249&Ne=4294957561&Ntt=PTC+resistor&Ntk=I18NAll&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&Ntx=mode%2bmatchallpartial&N=4294955123&Nty=1

Regards.

Yes, use the SMT types and bond them with the heaters.

they'll respond nicely.. bond them against the heater
resistors.

I don't know what it is with that sight you linked in how ever, it was
driving my browser crazy loading it.

http://webpages.charter.net/jamie_5"

Jan 27, 2009

On 25 Jan, 17:21, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

te...@hotmail.com wrote:
On 25 Jan, 14:55, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

On 25 Jan, 01:50, Jamie
jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

down load LTSpice.
copy and paste it into a xxxx.asc file.
open it with LTSpice.
remove all the garbag the readers put in there at the left.

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Hi
Ok Jamie I have done that (Thanks) & I can now see a circuit diagram.

I'm not sure what this is...is it a bespoke circuit for my needs?

Will this supply power to the heater until it reaches a determined
temperature (15 degrees C) ?

Sorry for all the questions but I'm lost with this stuff & really
don't understand.

Thanks.

U2 is a PTC "Positive Temperature Coefficient" resistor.
you'll want that close to the heater resistors which is
assumed to be on the Uc chip?

The PTC will increase in value as the temperature raises.
You need to shop around for the PTC from mouser, Digikey etc..
they come in various values and spec'd differently. for example
many are rated at what's considered room temperature, (25C)/77F.

R1 can be recalculated to match the PTC you get so that the voltage
at the network (- input) is just above the voltage at the (+) input
of the comparator at 15C. For example, 6.2 volts at (-) input at 15C would
be ok. you must think of this in terms of a voltage divider.

C1 and R4 is part of the timer, the two select the time and depth
of the threshold on the time cycle. You could actually omit these two
components from the circuit if all you want is a temperature switch.

If it's very cold, the PTC will most likely prevent the timer from
turning off the heaters until the PTC registers heat from the heater
resisters. If the temp is near the 15C, then the heaters will come on
and then off during the 5 sec window. As the initial temperature is
higher the timer will expire sooner, until at which point, the initial
temperature will be high enough to where the (-) input of the comparator
will be lower than the initial starting voltage at the (+) input, which
is calculated via the C1 and R4 and thus never turned on.

Q1, is a PNP power transistor. it must be large enough to handle
a 2 Amp load which shouldn't be a problem to locate..

The comparator used here, need not be the LTxxxx type here, you can
use others in place of it.
LM393 for example.http://i2c2p.twibright.com/datasheet/LM193.pdf

You could even use an old LM741 to drive it. It really does not
matter in this circuit...

http://webpages.charter.net/jamie_5"- Hide quoted text -

- Show quoted text -

Jamie thank you for your help, it's very appreciated.

Yes the heater SMD resistors are fixed to the top of the processor...I
plan to bond the PTC directly to the heater.

I noticed when looking up PTC resistors (Thermistor's) that some of
them have quite a high (30 seconds) TTC (Thermal Time Constant) will
this matter?

Do I need to get the lowest TTC I can find as from what I understand
this is the time that the Thermistor takes to react...is that correct?

Would a surface mount Thermistor be ok to use as this would be able to
bonded to the back of the heater quite easily...for some reason the
TTC isn't listed with the SMD versions I have seen.

Would you care to point me to the type I require...

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=249&Ne=4294957561&Ntt=PTC+resistor&Ntk=I18NAll&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&Ntx=mode%2bmatchallpartial&N=4294955123&Nty=1

Regards.

Jan 31, 2009

On 26 Jan, 14:39, John Fields <jfie...@austininstruments.com> wrote:

On Sat, 24 Jan 2009 16:20:35 -0800 (PST), te...@hotmail.com wrote:
On 24 Jan, 20:28, John Fields <jfie...@austininstruments.com> wrote:
I you have a sensor which measures temperature, why do you need a timer?

That is, if you turn on the power to the heater and then turn it off
when the sensor reads 15C what's the timer doing for you?

JF - Hide quoted text -

- Show quoted text -

Hi John,

Well I havent got either at the moment Im just exploring
possibilities.

I was going to build a timer to feed the heater for 5 seconds which
seems to be as long as the heater needs to be on for before the
processor starts to work. but then I though if I could control it via
temperature it would be a lot better.
The timer would trip & start to feed the heater but then once the
temperature reached 15 degrees C it would cut out regardless of what
the timer was doingso the timing wasnt so critical this would be a
lot more accurate than the 5 second blast that gets the processor
working.as I dont know how hot the processor gets in 5 seconds it
could be 40 degrees or it could be 50 degrees I dont know!

Ideally what I need is a circuit that only kicks in if the temperature
of the processor is below 10 degrees C & only stays on until it
reaches15 degrees C..that would be great.

---
One of the problems with circuits of this type is that the time lag of
the sensor will allow the temp of the device being heated to rise to
higher than the desired temp. As long as you don't overheat the device,
(or the heater) though, you should be OK.

One thing that troubles me is that your processor is unstable when it's
cold.

I don't think it should be, so it may be a problem with something
external, like the crystal you're using.

Which processor are you using and what's its clock source?

In any case here's a circuit which will do what you asked for:

(View in Courier)

+12V>--+--------+----------+----+-------------+-------+
| | | | | |
RTH1 | | | | | |
[15130] [30k] | [100k] [560] [5.5]
| | | | | |
| | +----|----|--[<1N4148]--|-------+
| | | | | | |
+-[100k]-|-----+---|+\ | E |
| | | | >--+--[1k]-----B 2N3906 |
| [10k]<--|---|-/U1A C |
| | | | LM393 | C
| | [0.1ľF] | +-----B
| | | | ZTX1048A E
[15k] [30k] | +--|+\ |
| | | | | >--+ |
| | | +--|-/U1B| |
| | | | | |
GND>---+--------+-----+----+--------+-----------------+

The thermistor is a Measurement Specialties 44006RC:

http://www.meas-spec.com/product/t_product.aspx?id=4062

and here's the LTspice circuit list so you can play around with it:

Version 4
SHEET 1 880 680
WIRE -560 -160 -704 -160
WIRE -320 -160 -560 -160
WIRE 0 -160 -320 -160
WIRE 80 -160 0 -160
WIRE 304 -160 80 -160
WIRE 464 -160 304 -160
WIRE -320 -144 -320 -160
WIRE 448 -112 416 -112
WIRE 528 -112 480 -112
WIRE -576 -96 -608 -96
WIRE -448 -96 -544 -96
WIRE 80 -96 80 -160
WIRE 304 -96 304 -160
WIRE 464 -96 464 -160
WIRE -560 -80 -560 -160
WIRE -336 -16 -384 -16
WIRE -224 -16 -304 -16
WIRE -320 0 -320 -64
WIRE 416 0 416 -112
WIRE 448 0 416 0
WIRE 528 0 528 -112
WIRE 528 0 480 0
WIRE -608 16 -608 -96
WIRE -576 16 -608 16
WIRE -448 16 -448 -96
WIRE -448 16 -544 16
WIRE 144 48 -96 48
WIRE 464 48 464 -16
WIRE 464 48 208 48
WIRE 304 96 304 -16
WIRE -224 112 -224 -16
WIRE 0 112 0 -160
WIRE -320 128 -320 80
WIRE -32 128 -320 128
WIRE -384 144 -384 -16
WIRE 80 144 80 -16
WIRE 80 144 32 144
WIRE 128 144 80 144
WIRE 240 144 208 144
WIRE 464 144 464 48
WIRE -560 160 -560 0
WIRE -528 160 -560 160
WIRE -160 160 -448 160
WIRE -96 160 -96 48
WIRE -96 160 -160 160
WIRE -32 160 -96 160
WIRE -320 192 -320 128
WIRE 400 192 304 192
WIRE -160 256 -160 160
WIRE -704 272 -704 -160
WIRE -560 272 -560 160
WIRE -384 288 -384 176
WIRE -336 288 -384 288
WIRE -224 288 -224 176
WIRE -224 288 -304 288
WIRE -320 336 -320 272
WIRE -704 432 -704 352
WIRE -560 432 -560 352
WIRE -560 432 -704 432
WIRE -320 432 -320 416
WIRE -320 432 -560 432
WIRE -160 432 -160 320
WIRE -160 432 -320 432
WIRE 0 432 0 176
WIRE 0 432 -160 432
WIRE 464 432 464 240
WIRE 464 432 0 432
WIRE -704 496 -704 432
FLAG -704 496 0
SYMBOL npn 400 144 R0
WINDOW 0 89 36 Left 0
SYMATTR InstName Q1
SYMATTR Value ZTX1048A
SYMBOL res 448 -112 R0
SYMATTR InstName R1
SYMATTR Value 5.5
SYMBOL voltage -704 256 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
WINDOW 3 24 104 Invisible 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 12 .001 .001)
SYMBOL res -336 320 R0
WINDOW 3 36 67 Left 0
SYMATTR InstName R3
SYMATTR Value 30k
SYMBOL res -576 256 R0
WINDOW 3 38 70 Left 0
SYMATTR InstName R4
SYMATTR Value 15k
SYMBOL res -336 -160 R0
WINDOW 3 40 67 Left 0
SYMATTR InstName R6
SYMATTR Value 30k
SYMBOL res -336 -16 R0
SYMATTR InstName R7
SYMATTR Value 5100
SYMBOL res -336 176 R0
SYMATTR InstName R8
SYMATTR Value 4900
SYMBOL res 288 -112 R0
SYMATTR InstName R2
SYMATTR Value 560
SYMBOL Comparators\\LT1017 0 144 R0
WINDOW 0 -42 66 Left 0
WINDOW 3 -87 98 Left 0
SYMATTR InstName U1
SYMBOL pnp 240 192 M180
WINDOW 0 85 62 Left 0
WINDOW 3 56 34 Left 0
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 224 128 R90
WINDOW 0 67 59 VBottom 0
WINDOW 3 67 62 VTop 0
SYMATTR InstName R9
SYMATTR Value 1k
SYMBOL diode 208 32 R90
WINDOW 0 -41 29 VBottom 0
WINDOW 3 -33 30 VTop 0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL res -432 144 R90
WINDOW 0 -29 56 VBottom 0
WINDOW 3 -28 59 VTop 0
SYMATTR InstName R10
SYMATTR Value 100k
SYMBOL res -576 -96 R0
WINDOW 0 49 44 Left 0
SYMATTR InstName R5
SYMATTR Value 15130
SYMBOL cap -176 256 R0
WINDOW 0 42 34 Left 0
SYMATTR InstName C1
SYMATTR Value 0.1ľF
SYMBOL res 64 -112 R0
WINDOW 0 -44 36 Left 0
WINDOW 3 -47 66 Left 0
SYMATTR InstName R11
SYMATTR Value 100k
TEXT -696 464 Left 0 !.tran 10
TEXT -216 0 Left 0 ;10K POT
TEXT 376 -136 Left 0 ;HEATER
TEXT -552 -120 Left 0 ;YSI 44006

JF - Hide quoted text -

- Show quoted text -

Hi.

John thanks for your information & diagram.

Yes the time lag is a very big consideration.thats why I specified
approx 15°C cut off.if the processor reaches double this it wont
matter & I would imagine it wouldnt go as high as that over?

To answer your questions

The processor is a Motorola MC68HC908AZ60.
The processor is on the circuit board in my car dash podit controls
the gauges & warning lights.
The processor wont start if the temperature is low so the gauges
wont work until the processor gets warmed up a little. Apparently
this problem affects a lot of vehicles from all manufactures that have
this processor controlling the dash pod.

From what I have read relating to the problem with this processor its
something to do with the way the processor has been programmed at
manufacture, I believe its been programmed out of spec which has
resulted in weak gate charge retention which can cause premature
failure after a couple of years or so...hence my problems.

The manufacturer of the processor (Freescale Semiconductor, Inc.)
advise that if the chip is erased & reprogrammed it will more than
likely fix this issue...I have read that if the processor is read at
room temperature (When it's working fine) and then reprogrammed with
this same dump it this could fix it.....unfortunately I have not got
the equipment to do this.

The car manufacturer (Renault) won't accept that there is a problem
with the dash pod...unlike Audi who suffered the exact same problems
form the same processor on the TT....they decided to offer a
replacement of dash pod regardless of the age of the vehicle.
There are a few companies that will fix the dash pod....but wheres
the fun in that!

Regards.

John Fields · Feb 1, 2009

On Sat, 31 Jan 2009 10:27:35 -0800 (PST), tel1e@hotmail.com wrote:

Hi.

John thanks for your information & diagram.

---
My pleasure,

---

Yes the time lag is a very big consideration.thats why I specified
approx 15°C cut off.if the processor reaches double this it wont
matter & I would imagine it wouldnt go as high as that over?

---
Freescale's automotive micros are spec 'ed to work from -40 to 125C,
so if you turned the heater off when the sensor got to 15C I don't think
there's any chance of the micro getting anywhere near 125C.
---

To answer your questions

The processor is a Motorola MC68HC908AZ60.
The processor is on the circuit board in my car dash podit controls
the gauges & warning lights.
The processor wont start if the temperature is low so the gauges
wont work until the processor gets warmed up a little. Apparently
this problem affects a lot of vehicles from all manufactures that have
this processor controlling the dash pod.

From what I have read relating to the problem with this processor its
something to do with the way the processor has been programmed at
manufacture, I believe its been programmed out of spec which has
resulted in weak gate charge retention which can cause premature
failure after a couple of years or so...hence my problems.

The manufacturer of the processor (Freescale Semiconductor, Inc.)
advise that if the chip is erased & reprogrammed it will more than
likely fix this issue...I have read that if the processor is read at
room temperature (When it's working fine) and then reprogrammed with
this same dump it this could fix it.....unfortunately I have not got
the equipment to do this.

The car manufacturer (Renault) won't accept that there is a problem
with the dash pod...unlike Audi who suffered the exact same problems
form the same processor on the TT....they decided to offer a
replacement of dash pod regardless of the age of the vehicle.
There are a few companies that will fix the dash pod....but wheres
the fun in that!

Right!

Good luck.

JF

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