ESP8266 Community Forum

- Wed Sep 09, 2015 2:38 pm #28732 Hi,

Very good explaination and nice design !

I didn't know that opto could include the reverse diod. For sure it's even nicer !

One question for you !
On my design I have noticed that the timing of the zero crossing is not fully symetrical :
ON half period is wider (lasts more) than OFFone.

As a consequence if I trigger an intrrupt on both edges then I can get timing issues leading to bad flicker.
Did you get the same problem ?

My solution was thus to only detect falling edge and then to compute delays for both half periods

JP

- Wed Sep 09, 2015 3:37 pm #28740 I think that the SFH620 that @trackerj is using doesn't simply have a reverse diode with the internal LED, it is a second LED placed in reverse, so the opto-coupler transitor is ON on both negative and positive phases, and OFF only during the zero-crossing, so it become symmetrical ...

- Wed Sep 09, 2015 3:50 pm #28743 Ok thank you --> it's clear now

JP

- Wed Sep 09, 2015 3:54 pm #28744 As I understand explanation in video https://youtu.be/pWzzti-9Llk?t=2m37s you are doing zero crossing detection on raising and falling edge for one half of sine and not for the other half. Therefore, because of forward voltage drop of LED, resulting pulses will not be in phase. Here it goes AC optocupler. But even with such optocupler there is a trap - please check great post by miceuz, under http://wemakethings.net/2013/10/27/triac-bloc/, chapter "Zero crossing detection".
You have a nice collection of interesting projects on your video on your channel
Good luck with your projects and troubleshooting of dimmer design!
Krzysztof