Hi all,

I have rigged up circuit which turns on light using MOC3021 optocoupler and BT139 traic , reference circuit in image 1.
Now i want make light get on / off based on motion detected by PIR sensor.
Issue is though bulb glows but it doesn't get switch off or switch on based on motion
PIR sensor gives output 3.3V and i am feeding this voltage to optocoupler , is there anything i should modify or add ?
Pls suggest.

 

You need to feed a DC supply to the Led in the Opto-coupler to make the light switch on. Can you post your pir circuit diagram, or model of pir sensor?

 

You need to feed a DC supply to the Led in the Opto-coupler to make the light switch on. Can you post your pir circuit diagram, or model of pir sensor?

I am using HCSR 501 PIR sensor .

 

It won't work as the pir only gives out a 3.3V pulse and already has a 1K output resistor, so you need a slave NPN transistor like this.....

 

It won't work as the pir only gives out a 3.3V pulse and already has a 1K output resistor, so you need a slave NPN transistor like this.....


View attachment 124031

Thanks for reply, i did that connected PIR output to base of transistor , bulb keeps glowing.
Does not get off or on based on PIR output....

 

Does the bulb go off with no DC power to the opto-coupler?

 

Although it Will work, a better choice of opto for that application is a zero cross version, rather than the 3021 random phase switch.
Max.

 

Does the bulb go off with no DC power to the opto-coupler?

No it wont go off even when DC to optocoupler is removed.! It seems optocoupler does not hold control on Bulb glow

 

Then your opto coupler is blown up.