Hi all. I have been trying to make a temperature sensor from a diode and my arduino uno. I have done a lot of googling and have got no where. I have tried two different approaches. The first approach with no prior research involves one diode and a resistor. The diode's cathode is connected to the arduino's ground and the diode's anode is connected to a resistor which connects to an arduino digital pin. I then have an arduino analog pin connect to the node between the resistor and the diode to read the voltage. So the equation for temperature is: T = [ q Vd ] / [ k ln( (Id+Is)/Is ) ] Where Id = (Vs + Vd)/R q = 1.61 x 10^-19 k = 1.38 x 10^-23 Vd is the voltage measured from the arduino analog pin and lastly Is is the reverse saturation current.
current "Is" is my issue since itself depends on temperature which is what I am trying to solve for. That is where I got stuck on that approach (is the equation a transcendental equation?).
After some research, I found valuable: page 338 of "The Art of Electronics 2nd ed." and http://en.wikipedia.org/wiki/Silicon_bandgap_temperature_sensor
For the art of electronics page 338, it shows circuits using transistors, is it possible to NOT use transistors for this project (op amp ok though)?
also looking over some forums online I read that an op amp is needed, is that true?
For my second approach I made two (almost) identical circuits with different resistors. The circuits resemble the one described above. Each circuit has it's own Vd connected to a different arduino analog pin. The resistors differ for each in order to have different currents flow through the diodes. I plan to use the second equation in the wikipedia link above, although I have a feeling that my second approach is super wrong.
Please help me out here. At least direct me where to go. Thank you.