Hello everyone,
I am trying to design a circuit that controls the state of a 12v relay using a microcontroller, the relay is operating using different source than the microcontroller, i've used an opto-coupler as an interface between input and output signal, but, the problem is that the opto-coupler is not transmitting the 12v needed for the relay to operate.
In the attachments there is a schematic of the circuit,View attachment opto.zip

Note: the optocoupler used is PC817

Thanks in advance,
z3ngew

 

What is it doing?
Use a type like the 4n35 series http://www.datasheetcatalog.org/datasheet/motorola/4N35.pdf

 

Maybe you can try to put the relay at the upper part (collector part).

 

Did you read the opt coupler data sheet? The maximum input current is 50mA and the minimum transfer ratio is 50% so the worst-case maximum output current is 25mA.

You circuit shows a 330Ω resistor in series with the opto input which gives about 11mA with a 5V signal so the worst-case output current is about 6.5mA, likely not enough to pull in the relay.

Bottom line is you probably need to add a transistor gain stage at the opto output to provide sufficient current to pull in the relay.

 

use any led/transistor type opto with this circuit here to switch your relay