I need help to detect an AC burned heater element

[Ioannis]

You did not followed exactly my thought.

Look at the attached schematic. You have to calculate the small resistor (I use SMD of 470 Ohms at 0805 size) according to bridge and Opto characteristics.

No need for power parts.

Light and dirty cheap.

The integrator or a simple delay will be done in software. When you have powered your load, current will flow through the bridge. A small voltage drop is then developed across the AC terminals of about 1,4-2 volts. The reverse voltage is small enough not to destroy the opto led.

So, when you have powered the load, normally the opto transistor will give a square waveform of line frequency. If the load is faulty, no current will flow and no pulses will be generated.

Ioannis

[Nicmus]

One other approach will be to do a search in this forum for “transformerless” you will find ideas of simple circuits of powering up small loads (a LED part of the optocoupler in your case) .
Use one of the circuits in parallel with your switching device (relay, triac,…etc) and monitor its control signal and the optocoupler output.
If your heater is OK you will have a signal from your optpcoupler when the heater is not energzed. In case the heater is open you get no signal when the controlling device is OFF.

HTH

Nick

[igeorge]

Thank you Nick
I will look on this too. It might be a good solution to get rid of the power components problem
Regards
Ion

[Nicmus]

Using one of the modules, suggested above, parallel with the switching device and one parallel with your load and ORing the outputs of the optocouplers (preferably open collector type) you can have all your parts inside your machine and the only connections to the monitoring device will be two isolated wires that will act as a “switch”. The only time the “switch” shows open will be when your heater is open.

Nick