Isolation using relay and teensy 4.1

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M

mar

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relay.jpg

I purchased this 3V relay so that I could control some 120V accessories for a cnc project I'm working on.

After some digging, I found this diagram that I followed to wire everything up.

schematic.png

It works fine, and I can turn on and off my accessories, but I'm wondering if I'm actually isolating the two circuits. Here is my wiring:

wiring.png

My question is, am I supposed to connect the ground of the external power supply to the ground of the teensy?

Any help would be appreciated. Thanks.
 
3vrelay.png

According to this schematic from Amazon which may or may not be correct, you do not need the ground connection from the external power supply to the Teensy. BUT your external supply should be 3.3 volts instead of 5 volts.
 
Thanks for your reply rcarr!

My mistake on the external power supply. I am using a 3V source.

However, would you mind telling me why I don't need to connect the grounds together? I've learned to always connect all grounds together for the projects I've worked on.

Thank you for your help.
 
The circuit has an opto-isolator which consists of a light emitting diode and photo sensitive transistor. When the jumpers are off, the Teensy will be totally isolated from the relay power supply - the connection to operate the relay is via the light from the diode to the photo transistor.

If you are powering other devices with your 3.3 volt supply and they are interfaced with the Teensy but not using opto-isolators, you will need to connect the grounds.
 
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