arduinoraspberry piresistance
I have a wire whose temperature I will change. This will change its resistance, but I want the same amount of current flowing through. I was thinking of having some kind of variable resistor in series with this which would detect the current flowing through the circuit, and adjust its own resistance accordingly so that the current remains constant.
I was thinking of somehow using an Arduino or raspberry pi, but I wasn't able to find any way to do so. Any tips?
YOu are entering a world where Electro Magnetic Compatibility is at risk. Pay attention to the stray current spikes that radiate noise (Egress) and their influence on other circuits of high impedance (Ingress). YOu probably also have ripple or the conducted egress and ingress as well.
For radiated noise a handy tool is a small AM radio (not FM) nearby, to locate such noise issues if you dont have a scope.
Noise suppression management may include some common mode chokes to the track or pot lines. Perhaps some supply rail filtering may need to be added around the track.
I would use ferrite beads for each driver with caps after the bead and then use twisted pairs to send the current after going thru a ferrite torroid or similar common mode choke, like those used in Video cables. Its good to have a kit of parts for such issues.
Add decoupling caps to the breadboard for both sides.
You could use an op-amp as a buffer/voltage follower, then put whatever scaling you need after the follower. The high input impedance of the buffer shouldn't appreciably load the thermistor circuit.
simulate this circuit – Schematic created using CircuitLab
Best Answer
You made something simple look complicated. You need to feed the resistor through a current generator. There are many schematics available on the net. I suppose you want to have a ground point to measure voltage on the wire then compute the temperature from it.
Which solution you use is highly dependent on wire resistance and current needed.
For small wire voltages you can use a simple resistor, For V1 >> Output voltage and R1 >> R_wire the circuit is a very good approximation of a current generator, for wire resistance between 0 and 0.2ohm the I error is in the range of 0.2%
simulate this circuit – Schematic created using CircuitLab
If the wire has a higher resistance or you need a higher voltage you can adjust R1 to obtain the voltage or current you need. The error would be given by (delta R wire across temperature range)/R1.
If the wire resistance is higher and you need voltages that are not much less lower than the power supply voltage then use a current generator like this one or search google for current generator.