Hopefully someone can throw some ideas out about this project. I have a propane/LPG powered absorption fridge but the sight glass doesn't work for whatever reason, the only way to check the burner is lit is by removing an access panel at the back of the fridge and looking at the burner.
So I thought it should be simple enough to make a circuit that detects the light from the burner and turns on an LED at the front of the fridge.
I've been doing this for days now! Everything I have tried does not work.
First attempt was a LDR and a NPN transistor amplifier, but there isn't enough light coming from the burner to trip the circuit. In use, the burner is in total darkness. However, the flame is blue (propane).
I read on one post that the spectrum of a propane flame tends to the infrared. I got some IR photodiodes but testing them on the bench using a blue propane flame doesn't seem to work either.
I've ordered a K-thermocouple, but all the circuits use IC's to measure temperature. I don't need to know the temperature, I just want an LED to indicate that the burner is lit!
Has anyone got a simple circuit that works on 12v DC, preferably using a transistor etc, that could do this for me?
I'm at the stage now where I am planning on buying a universal thermostat with a thermocouple probe that switches on/off at 50-150C