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Bargain Basement / Re: larger mill, lathe available
« on: June 01, 2021, 06:30:43 AM »
Are you just wanting them gone? If so, might be able to do something.
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A reasonable solution
Steve, that diode is not across relay coil
Attached is the schematic how it should be connected.
BTW I don't like the routing, and you have a common ground which voids opto isolation.
Even your board does not look like schematic that you used.
What is the 12pin connector for? Are you going to place wire links from that one to 8pin one to establish connection for series resistors for opto couplers?
The PCB traces to the relay contacts could be wider, especially the one from the 24V input which is common to all. I am guessing you will have only light logic level loads but if you control large solenoids that should be addressed. A dead short might destroy the common trace, a fuse would be good if your 24 volt supply can supply high current.
There are multi-relay opto isolated boards on eBay that would likely fit your needs.
If you have parts and are trying to save this design tell us more about what you are connecting to the inputs and outputs.
The external diode is not needed in this case. There is a diode inside the ULN2803 between the output and its COM pin which is intended to serve this purpose. Just connect the COM to your +24V or whatever is the positive supply of the relays.