George,
Each of the 5-volt relays draws between 0.065 and 0.070 amps. I would allow 1/2-amp per 8-relay module just in case all the relays are energized at the same time.
Stan,
Your diagram is correct - use the (-) of the power supply to pick up the relay.
Dale,
That's what I did, except I used 12-v relays. I built five such 6-relay modules with the 12-V coil relays, but the next three will be the 8-relay modules even though I will have an extra two relays. Still, the cost of the modules I built was around $20 (relays, terminal strips, connectors, etc.) and about two to three hours of building time.
The 'other' 8-relay modules, with the 5-volt relays, are ready to go as purchased for about $10. They have fly-back diodes (as my home made ones do) but they also have the optically isolated relay inputs, which mine do not. (I used Form-C contact relays for my modules as they were about as cheap. The 5-volt relays also have Form-C contacts.)
Here are both home made and purchased:
(Click for larger size)
Good thread, BTW.
Alex
