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Topic: Devices to salvage thermistors from? (Read 481 times) previous topic - next topic

aarg

Harvest diodes and transistors. They can also be used as thermal sensors - I've made and calibrated one. The junction voltage varies linearly with temperature which is handy compared with the non-linear response of thermistors. An LM35 sensor is basically just a junction with an amplifier on it.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

brodbord

Harvest diodes and transistors. They can also be used as thermal sensors - I've made and calibrated one. 
Ok! How do you wire it? 

larryd

No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

brodbord

#18
Jan 18, 2021, 04:13 pm Last Edit: Jan 19, 2021, 11:45 am by brodbord
" Ok! How do you wire it? "

Google is your friend:

https://www.google.ca/search?q=transistor+temperature+sensor&client=safari&hl=en-ca&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjYs-zcupnuAhVgGDQIHQpaC3IQ_AUoAXoECCEQAw&biw=1269&bih=834&dpr=2      
Thank you, I appreciate it. But I need some more help on setting this up with ny Nano.  I'll attach an image from my breadboard attempt [EDIT: removed it]. Green wire goes to A0. First attempt I had no diode and the transistor got very hot. I get some reading on A0 but it is not really changing.  

larryd

No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

aarg

...instead of a reverse biased diode...
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

brodbord

...instead of a reverse biased diode...
Opps... 
I got it working now, except that the sensitivity is much lower than the 10k thermistor. Actually the sensitivity is so low that the serial output is barely changing. But I can read it with a multimeter: Like 0.xxx V where the two last digits change by touching and holding the transistor. This should work if I just could raise the signal. What options are there? Can you do it in arduino code, or should it be done in the circuit?
Thanks!

Paul__B

So you are now using the 1.1 V internal reference, are you not?

brodbord

#23
Jan 19, 2021, 02:13 pm Last Edit: Jan 19, 2021, 09:33 pm by brodbord
So you are now using the 1.1 V internal reference, are you not?
I am not sure what that means, sorry. [EDIT: Now I do, found it in the manual... ]
I attach another breadboard picture (I know it is not the preferred way of showing a circuit) to illustrate how I wired it. It is fed with 5v from the Arduino Nano. The transistor is a bc547b.


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