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 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.
This is a most excellent approach.
Rather than introducing a variable resistor, why not strip some of the wire of its insulation and attach it to a metal capstan (with a tensioning spring). A stepper motor winds in the capstan, making the wire shorter and keeping the resistance constant.
An RPi would let you display the resistance on a monitor.
Alternatively you could skip the RPi, use a dc motor and an opamp,
simulate this circuit – Schematic created using CircuitLab
and since the current is constant, just write it on cardboard so it is low power, sunlight readable and non volatile.
