Remote Mains PWM

[ardhuru]

They are there to protect the optos incase the wires are connected incorrectly.

With a 1K resistor in series with the pic output, I dont think you would damage the opto LED even if connected reverse. I'm not saying removing the diodes is a solution, just that I think they are redundant.

Anand

[The Master]

With a 1K resistor in series with the pic output, I dont think you would damage the opto LED even if connected reverse. I'm not saying removing the diodes is a solution, just that I think they are redundant.

Anand

I thought that too. In previous circuits that use optos i once connected one the wrong way and it never worked after i corrected it. I dont know for sure that the reverse current caused it as i had never turned it on before wriring it the wrong way. It could easily have been damaged by overheating during soldering or it might have been a bad component when it arrived.

The triacs/optos are inside the light holders and its very fiddly to replace them. I have thousands of diodes laying around and they cost almost nothing so its well worth including them just incase.

[HenrikOlsson]

Hi,
Figuring you have a MOC3020 opto-coupler the maximum reverse voltage according to the datasheet is 3V so it's possible it got damaged by connecting them backwards. But instead of having the diode in series like you have it now place it anti-parallell with the opto-coupler LED. Then it will clamp the reverse voltage to ~0.7V and the series resistor will limit the current.

As you have it now..... Figuring 5V output from the PIC, 0.7V drop across your series diode, 1.15V drop across the LED we have 5-0.7-1.15=3.25V left across the 1k resistor. This yields a forward current thru the LED of 3.25mA. Although this should work as long as the "firing pulse" thru the LED is at least ~6us or so it just "feels" a bit low to me. Why not simply try with a 330ohm resistor or something?

Now, if you have another optocoupler then obviosuly the above numbers may not be correct but it might be worth looking into it for your particular device then.

/Henrik.

[The Master]

I dont remember exactly which optos im using. They have been in the lights since last year. I think they are MOC3020 or MOC3020X.

You are right about it being a low voltage problem. The 1K resistors are fine. Ive used those in every mains PWM circuit ive made and they work fine. The resistors are also in the lights along with the diodes, optos and triacs. The problem is that for some reason i have more 1K resistors in the controller. I just tried shorting them out and the lights stopped flickering and started fading correctly.

Ive been on and off this circuit for over a month now and it turns out to be something as simple as that :P

Thanks a lot for helping me solve this!