[SOLVED] 8051 and moc3021 , led stays on

[sunil21]

Last year for Christmas I did chaser circuit with AT89C4051+bc547+BT136, it was not recommended by this forum, (I was warned against bringing MC in contact with mains supply) was told to use an optocoupler.
It just worked and was not perfect.

And now - For using opto, as a prelim, I used PC817 separately , I connected it to 5v supply using 560ohm resistor and on the other side I connected led thru 180 ohm resistor,. when I give 5v supply to pin1 of opto led light up and go off when the 5v opto supply is cut.

I read in this forum, with BT136 it is better to use MOC3021. so did I, removed pc817 and used moc instead, but when I give supply to moc , led light but stays on even after I remove Moc supply. is this "zero cross something".. I went thru this forum, but didn't get a clear answer.

 

[jayanth.devarayanadurga]

It is a Opto TRIAC. Once triggered it remains ON till the Anode current is made less than holding current. Use transistor type opto isolator like 4N35.