LED relay opto-coupler MCU connection

[fshgtai]

Hi, I am working on a design that uses a relay to control LED lights. The schematic shows +12VDC LEDs connected to (+) of terminals, the other end (-) of terminal is connected to an opto-coupler and relay, which feeds into the MCU. I only see a high signal at the opto-coupler output whether the relay is on or off. I'm not sure what the issue is with the attached circuit. Can anyone help me identify and rectify the problem? I have already designed a PCB with this circuit and would like to avoid repeating the same mistake in the new build. Thank you

 

[betwixt]

The schematic isn't attached, please try sending it again. Without it the question is ambiguous because we can't tell whether you are driving the opto coupler or reading from it.

Brian.

 

[D.A.(Tony)Stewart]

These are so cheap now, why make your own $1~2 /channel https://www.temu.com/ca/12v-1-2-4-8...tb&refer_page_sn=10032&_x_sessn_id=bp8radrynk

 

[betwixt]

Just a word of caution, as in Tony's schematic, on some commercially available relay boards there is no isolation between input and output grounds. Fine if your load has to be switched to the same ground as the input but bad news if the ground side of your load is connected elsewhere.

Brian.

 

[KlausST]

Hi,

controlling 12V LED lights, neither needs an optocoupler nor a relay. A simple MOSFET could do.

***

I personally call it useless to drive a relay from an optocoupler that is used in non_isolating configuration.

Klaus

 

[aliarifat794]

Check the voltage levels at the input of the opto-coupler when the relay is turned on and off. If you're only seeing a high signal regardless of the relay state, there may be an issue with the input signal to the opto-coupler.