arduino and relay battery power sketch

Can someone sketch me how the connections should be for an arduino to run a relay and use an external battery. I'm horrible at the electrical aspect of it. I can make it work while connected to the laptop but can't when using a 9v battery. Just wanted to see how some others would connect it and make it work?

This is what I have so far. I know I shouldn't use the arduino to power the servo and relay. Need some guidance on how to do that... thanks

The Vcc of your relay board needs to be that of the relay voltage. I suspect that 3.3v is too low for the relay.

Describe what you mean by not working. What happens or doesn't happen?


What kind of “RELAY” ?
SSR = Solid State Relay
Coil = Magnetic Relay

What voltage is needed to turn on the relay?

I don’t understand the 3 inputs:

  1. Power
  2. Signal
  3. Ground
    that are connected to the relay.

Usually, a Relay is connected with only two wires:
a) Power and a Pull-Low Output
b) Ground and Pull-High Output

Power the servo from a separate power supply, being sure to connect all the grounds together.

Because the "relay" has Vcc, Gnd and input, I assume it to be a shield.

I would expect 5v or 12v for Vcc.


The servo is a Vilros mircor servo 9g sg90. I just dont understand how to use the external battery and still have all the grounds connected.

I'm sure the relay needs more than 3.3v but I don't see how to get power to it when it only has a vcc pin.

Here is a little bit of what I'm working with... However I don't power the arduino with 8AA anymore... burned my last one up doing that. But I do want to run the h20 pump with the 8aa batteries.

Read the spec on the relay board, that should have the required Vcc. What voltage are the relay coils?

The relay Vcc does not have to be the same as the Arduino. As long as all gnd points are connected, you can have different voltages to different boards. Just check what voltage is needed on each.

As far as connecting grounds, you need a common connection between the boards, this is gnd. Simply wire them all to a common point.