Temperature sensor for solar dryer heat control
try this; if the diodes are even close to working as diodes, the hot diode voltage will drop by 200 * 0.002 = 0.4 volts when heated to 200 degree C.
Simply measure both voltages, subtract, divide y 0.002 (or 0.0022?) and you'll have a somewhat accurate and cheap temperature estimate.

Is this cheap enough? Calibration is up to you. 







simulate this circuit &ndash; Schematic created using CircuitLab