Homebrew PCBs

I have modified my PIC based temperature control to use a K thermocouple instead of a LM34. I used an AD595 chip to linearize K thermocouples to 10 mV/*C. This is a simple circuit using a PIC12F683 for analog input and a PWM output to a digital panel meter for display of temperature and set point. Two switches are use to set the temperature. Normaly the temperature is displayed. When either the increment or decrement switch is pressed the unit displays the set point and allows it to be changed. A relay with on/off control keeps the overshoot to less than 8 degrees C.

I changed to thermocouple input when i needed temperatures in the 160 *C + range. 

The AD595 and K thermocouple can be obtained from Spark Fun Electronics. Tho not cheap.

RD

In this kind of application it is often acceptable to work without
cold junction compensation. (Room temperature variations would be
inside acceptable temperature error). That way you could avoid the
costly AD595.

Another alternative would be to use a thermistor instead, one suitable
for this temperature could be found in every laser printer at the
fuser roller.

ST

On Sat, Dec 26, 2009 at 6:34 PM, rdheiliger <rdheiliger@...> wrote:
> I have modified my PIC based temperature control to use a K thermocouple instead of a LM34. I used an AD595 chip to linearize K thermocouples to 10 mV/*C. This is a simple circuit using a PIC12F683 for analog input and a PWM output to a digital panel meter for display of temperature and set point. Two switches are use to set the temperature. Normaly the temperature is displayed. When either the increment or decrement switch is pressed the unit displays the set point and allows it to be changed. A relay with on/off control keeps the overshoot to less than 8 degrees C.
>
> I changed to thermocouple input when i needed temperatures in the 160 *C + range.
>
> The AD595 and K thermocouple can be obtained from Spark Fun Electronics. Tho not cheap.
>
> RD
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>

Yessss Sir ! 
Just found one in a Laser Printer dismantled to make a laminator , was just wandering if it could be used for a noble scope like this one .... 
I'm also trying to build a laminator with thickness control from the remains of the said laser printer , I can't find a cheap laminator in my city , min price is 150$ , no Staples here in italy (sniff) and by the way the cheap ones are almost impossible to modify .
I'll keep the group informed.
BTW the laminator I'm using now is indeed very cheap (40$) but the PCB is too thick and the gears can't keep up with and they loose traction .
Beside this small problem , it's working a beauty with the thermostat retrofitted so it can reach 180 C° to fuse the toner . I'm using TT paper the blue one.

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:

> 
> Another alternative would be to use a thermistor instead, one suitable
> for this temperature could be found in every laser printer at the
> fuser roller.
>

Stefan, are you saying connecting a Type J (or K) Thermocouple direct to an analog input pin using a PIC12F683?  What about a AVR chip such as a ATmega168 or similar?  Perhaps using the internal 1.1 reference voltage?  I wasn't sure the analog input would be sensitive enough to read the low mV of a thermocouple.

Thanks for any input.

Ken H>

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:

>
> In this kind of application it is often acceptable to work without
> cold junction compensation. (Room temperature variations would be
> inside acceptable temperature error). That way you could avoid the
> costly AD595.
> 
> Another alternative would be to use a thermistor instead, one suitable
> for this temperature could be found in every laser printer at the
> fuser roller.
> 
> ST
> 
> On Sat, Dec 26, 2009 at 6:34 PM, rdheiliger <rdheiliger@...> wrote:
> > I have modified my PIC based temperature control to use a K thermocouple instead of a LM34. I used an AD595 chip to linearize K thermocouples to 10 mV/*C. This is a simple circuit using a PIC12F683 for analog input and a PWM output to a digital panel meter for display of temperature and set point. Two switches are use to set the temperature. Normaly the temperature is displayed. When either the increment or decrement switch is pressed the unit displays the set point and allows it to be changed. A relay with on/off control keeps the overshoot to less than 8 degrees C.
> >
> > I changed to thermocouple input when i needed temperatures in the 160 *C + range.
> >
> > The AD595 and K thermocouple can be obtained from Spark Fun Electronics. Tho not cheap.
> >
> > RD
> >
> >
> >
> > ------------------------------------
> >
> > Be sure to visit the group home and check for new Links, Files, and Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
> >
>

No, amplify it with an opamp first.

Some atmels come with up to x200 internal amplifier now, not sure if
that would work.

ST

On Tue, Dec 29, 2009 at 1:06 AM, sailingto <sailingtoo@...> wrote:
> Stefan, are you saying connecting a Type J (or K) Thermocouple direct to an analog input pin using a PIC12F683?  What about a AVR chip such as a ATmega168 or similar?  Perhaps using the internal 1.1 reference voltage?  I wasn't sure the analog input would be sensitive enough to read the low mV of a thermocouple.
>
> Thanks for any input.
>
> Ken H>

Thanks for the info - since I'm not sure about how to build an Opamp circuit, I found some thermosistors on digikey I think I can use.  They are 1,000 ohms at 25C and 2300 ohm range at 175C.  I think I can get decent control....  maybe I should say "sufficient" control? 

I should be able to show temperature on a LCD display and control a relay both with that for a temperature controller.  I'll work on that.

"IF" I knew which AVR chip had a 200x internal amplifier I "think" I could make a type J thermocouple work with that.  I've got a couple feet (or 3ft?) of type J lying around.

Ken H>

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:

>
> No, amplify it with an opamp first.
> 
> Some atmels come with up to x200 internal amplifier now, not sure if
> that would work.
> 
> ST
> 
> On Tue, Dec 29, 2009 at 1:06 AM, sailingto <sailingtoo@...> wrote:
> > Stefan, are you saying connecting a Type J (or K) Thermocouple direct to an analog input pin using a PIC12F683?  What about a AVR chip such as a ATmega168 or similar?  Perhaps using the internal 1.1 reference voltage?  I wasn't sure the analog input would be sensitive enough to read the low mV of a thermocouple.
> >
> > Thanks for any input.
> >
> > Ken H>
>

This is why I went with a single-chip solution that converted a
thermocouple to a "degrees C" SPI digital output.  No analog, no math,
no guessing...

<http://www.nhsouth.com/crafts/workbench/thermocpl.htm>

If you need an output referenced to zero this would be a better circuit:
<http://circuits.linear.com/images/60789_TA01a.JPG>

You can leave out the LT1025 if you don't need cold junction
compensation and connect to ground instead.

There's a soldering iron temp control circuit on the E_101 list, works
just fine for a laminator:
<http://f1.grp.yahoofs.com/v1/gAg7S0za6gl3TT5Ydgb_GpwD3zXiCQbn_JBa5sm7Ttd6Yau1fx5nvLt6I8Wxcw5TBnPZF0P4miAvCkPh1EJPAVMu67omGp37ZhPsRA/Adrian%27s%20stuff/DIY%20Soldering%20Station/Termostat%20Schematic.pdf>

<http://groups.yahoo.com/group/Electronics_101/files/Adrian%27s%20stuff/DIY%20Soldering%20Station/>

But the thermistor will work too, you could probably connect a voltage
divide made of it directly to an ADC.

If you have the opamps and soldering iron out anyway, why not make an
analog controller? You are 90% done already.

ST

On Wed, Dec 30, 2009 at 3:06 AM, sailingto <sailingtoo@...> wrote:
> Thanks for the info - since I'm not sure about how to build an Opamp circuit, I found some thermosistors on digikey I think I can use.  They are 1,000 ohms at 25C and 2300 ohm range at 175C.  I think I can get decent control....  maybe I should say "sufficient" control?
>
> I should be able to show temperature on a LCD display and control a relay both with that for a temperature controller.  I'll work on that.
>
> "IF" I knew which AVR chip had a 200x internal amplifier I "think" I could make a type J thermocouple work with that.  I've got a couple feet (or 3ft?) of type J lying around.
>
> Ken H>
>

When I looked into using thermistors for laminator temp control, I looked at the maximum temperature spec of the thermistor. Few of them can withstand 170 *C. The glass bead type seem to be the only thermistors capable of going that high. They then get expensive and hard to find. Believe that is why Steven suggested pulling one out of an old laser printer fuser unit. Also, one needs to calibrate and linearize the thermistor output. Meaning, one needs to have some other accurate instrument to develop a lookup table. The same goes for using a thermocouple and an opamp. I personally decided that $30 for the AD595 and a thermocouple was worth not hassling with other methods. 

One could always just buy a rheostat and keep turning up the heat until one gets a good transfer and not worry about the actual temperature. Since a good transfer is the desired end result. Perhaps we some times over engineer things????????????


RD

[Non-text portions of this message have been removed]

There's no need to linearize, calibrate, etc., all that matters for a
thermostat is that is keeps the same temperature (or close enough).

I don't think it could be reasonably done with a rheostat without
waiting a long time for things to settle. Would be just as worthless
as those soldering irons without temperature control.

I always say closed loop controls greatly improve the value of any
tool. We'd see them more often if people still knew how to make them
without an over-engineered approach that'll be way to expensive  ;-)

If you have as much as $30 to throw at this you may as well save
yourself the bother and just buy the full-blown ready made PID
controller on ebay:

<http://cgi.ebay.com/Dual-Digital-PID-Temperature-Controller-Kiln-Furnace_W0QQitemZ110475096602QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item19b8d4321a>


ST

On Wed, Dec 30, 2009 at 5:11 PM, RDHeiliger <rdheiliger@...> wrote:
> When I looked into using thermistors for laminator temp control, I looked at the maximum temperature spec of the thermistor. Few of them can withstand 170 *C. The glass bead type seem to be the only thermistors capable of going that high. They then get expensive and hard to find. Believe that is why Steven suggested pulling one out of an old laser printer fuser unit. Also, one needs to calibrate and linearize the thermistor output. Meaning, one needs to have some other accurate instrument to develop a lookup table. The same goes for using a thermocouple and an opamp. I personally decided that $30 for the AD595 and a thermocouple was worth not hassling with other methods.
>
> One could always just buy a rheostat and keep turning up the heat until one gets a good transfer and not worry about the actual temperature. Since a good transfer is the desired end result. Perhaps we some times over engineer things????????????
>
>
> RD
>

Dear RDHeiliger 

  I had to comment because I personally feel you "hit the button" so to say with your commnts, particularly with the last sentence, where I feel if DC is used (or the heater supply is converted  to DC if AC), one could build a very cheap Pulse With Modulator from say a 555 chip and a handfull of other compnents.....and once the trimmer has been set, there will probably be little need to change its setting.....of course if one had a thermometer that can read to say 200°C as a seperate unit, one could check out the temperature....

  There are some very cheap Non contact Laser versions that can read to almost 400°C for very little money on ebay for example, look here:-

  http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250528259516

  For less than $16.........thats cheap!!!

  regards

  Andy
  ----------------------------------------------
  When I looked into using thermistors for laminator temp control, I looked at the maximum temperature spec of the thermistor. Few of them can withstand 170 *C. The glass bead type seem to be the only thermistors capable of going that high. They then get expensive and hard to find. Believe that is why Steven suggested pulling one out of an old laser printer fuser unit. Also, one needs to calibrate and linearize the thermistor output. Meaning, one needs to have some other accurate instrument to develop a lookup table. The same goes for using a thermocouple and an opamp. I personally decided that $30 for the AD595 and a thermocouple was worth not hassling with other methods. 

  One could always just buy a rheostat and keep turning up the heat until one gets a good transfer and not worry about the actual temperature. Since a good transfer is the desired end result. Perhaps we some times over engineer things????????????

  RD

[Non-text portions of this message have been removed]

"RDHeiliger" <rdheiliger@...> writes:
> One could always just buy a rheostat and keep turning up the heat
> until one gets a good transfer and not worry about the actual
> temperature.

In my case, I also use the laminator for photofilm, and then the
actual temperature is much more important - 240F for dry laminating
and 205F for wet laminating.  The spec sheets tell you what temp to
use, it's a lot easier when you can just set it to that temp and get
it right the first time.

Remember that PWM alone does not constitute closed loop control, it is
open loop. You still need some way to measure the temperature and
adjust the PWM to keep it constant, but that measuring does not have
to be converted to degree or anything, all you need is hold the same
point.

Thank you for the link to the extraordinarily cheap IR thermometer. I
was looking for one but my usual Chinese source was not cheap enough.
Hadn't thought of ebay for some strange reason. Note these
thermometers are not very accurate since they depend on emissivity of
the surface measured, but I'll still be buying that unit, thanks
again!

ST

On Wed, Dec 30, 2009 at 6:45 PM, Andrew Mathison
<andrewdavid.mathison@...> wrote:

>  Dear RDHeiliger
>
>  I had to comment because I personally feel you "hit the button" so to say with your commnts, particularly with the last sentence, where I feel if DC is used (or the heater supply is converted  to DC if AC), one could build a very cheap Pulse With Modulator from say a 555 chip and a handfull of other compnents.....and once the trimmer has been set, there will probably be little need to change its setting.....of course if one had a thermometer that can read to say 200°C as a seperate unit, one could check out the temperature....
>
>  There are some very cheap Non contact Laser versions that can read to almost 400°C for very little money on ebay for example, look here:-
>
>  http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250528259516
>
>  For less than $16.........thats cheap!!!
>
>  regards
>
>  Andy
>  ----------------------------------------------
>  When I looked into using thermistors for laminator temp control, I looked at the maximum temperature spec of the thermistor. Few of them can withstand 170 *C. The glass bead type seem to be the only thermistors capable of going that high. They then get expensive and hard to find. Believe that is why Steven suggested pulling one out of an old laser printer fuser unit. Also, one needs to calibrate and linearize the thermistor output. Meaning, one needs to have some other accurate instrument to develop a lookup table. The same goes for using a thermocouple and an opamp. I personally decided that $30 for the AD595 and a thermocouple was worth not hassling with other methods.
>
>  One could always just buy a rheostat and keep turning up the heat until one gets a good transfer and not worry about the actual temperature. Since a good transfer is the desired end result. Perhaps we some times over engineer things????????????
>
>  RD
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>

That looks like a neat circuit. I have bookmarked it for later.

Thanks for the info and  help - I also just joined Electronics_101 group.  Looks like a good group.

Ken H>

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:

>
> <http://www.nhsouth.com/crafts/workbench/thermocpl.htm>
>

At 11:45 AM 12/30/2009, you wrote:
>
>There are some very cheap Non contact Laser 
>versions that can read to almost 400°C for very 
>little money on ebay for example, look here:-
>
><http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250528259516>http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=250528259516
>
>For less than $16.........thats cheap!!!

shipping on this is $9 = $25 total. you can get a 
Ryobi at Home Depot in tool department for $29 
and if it breaks or doesn't work, they will exchange.

~ William 

[Non-text portions of this message have been removed]

Plane tickets are cheap now, but not _that_ cheap for a transatlantic flight ;-)

If I bought it locally it would cost 5 times that. Amazon would ship
the Ryobi, but not for $29.

I found the same on with a little cheaper shipping, $20 overall.

ST

On Thu, Dec 31, 2009 at 5:57 PM, William <walford@...> wrote:

> shipping on this is $9 = $25 total. you can get a
> Ryobi at Home Depot in tool department for $29
> and if it breaks or doesn't work, they will exchange.
>
> ~ William
>