One power supply and different nodes

Other Hardware General Electronics
1

I really should know this, but I was hoping someone could confirm (or set me straight) on what I'm thinking. I have a 24V power supply. Say I have three switches in parallel - each on a node of the 24VDC. On each switch leg is a 24V relay (coil is 2.2k). [The contacts of each are what the dig pins of an Uno see and are not my concern at this point ...] I think when I look into one of the switches, I might see one of the coils if a switch is closed. My thought is that I place a diode on each leg. Does this sound appropriate?

Thanks in advance.

2

Draw a picture - I can't follow that description.

3

Thanks for the reply. Attached is a quick sketch. I thinking D1,3,6 are needed to prevent loading each node. My simulation isn't working so I'm not as excited as I was before. The leds/resistors are just for sim testing as I would instead use pulldown resistors to the digital ins of the Uno.

test_circuit.JPG
test_circuit.JPG971×740 244 KB

4

This is what you want, excluding the Arduino cctry.

Relay.jpg
Relay.jpg949×496 139 KB

5

So I need the flyback diode? In your sketch - if switch 1 was closed and I looked into the circuit of switch to open ( and 3 is open) would I see the coil resistance of relay 1? Many thanks to both who replied.

6

Yes, diode is needed.
You have 3 circuits in parallel - so if 1 switch is closed, then looking from the 24V source you would see the coil.

Will you have switches as drawn? On NPN transistors on the Gnd side to sink the relay coil current to Gnd?

7

I will have the switches as drawn, and I hoped to keep it really simple ... if you think I need the transistors then I have to find a lot of books that I haven't looked at in a while. I thinking Beta = Ic/Ib, right?

8

If arduino is not controlling the relays, then no transistors are needed.

9

Thanks for your help!