What I am trying to do today is control one circuit using another, with no common ground or voltage between the two circuits. Basically what I am looking for is some way to have my Arduino, powered off of its own battery, control a 24V led circuit without using a voltage regulator.

It seems like I am looking for somewhat of a hybrid between a relay and a transistor, the relay providing the ability to control current in a circuit from a separate setup, and the transistor providing a solid-state variable current setup (in this case, hopefully also with signal amplification. If need be, though, I could always just use BJTs)

I apologize if there is something like this already on the forum but I could not think of what I should search for, and my searches turned up nothing.

Thanks in advance,


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    \$\begingroup\$ Can I introduce you to these little guys called optocouplers ? nl.wikipedia.org/wiki/Optocoupler \$\endgroup\$ Sep 8, 2015 at 13:38
  • \$\begingroup\$ You haven't described in your question why you can't have a common ground between the two devices. Can you elaborate? \$\endgroup\$ Sep 8, 2015 at 13:40
  • \$\begingroup\$ if you don't want a physical connection between control circuit and receiver, then you have to have some other connection, such as RF transmission, opto coupling as FakeMoustashe mentioned, or low frequency magnetic pulses. These are all still "connections" mind you, they are just referred to as WIRELESS connections. \$\endgroup\$
    – Randy
    Sep 8, 2015 at 14:48
  • \$\begingroup\$ Optocouplers are what I originally had in mind but just connecting the grounds was all I needed to do. My bad for overthinking things but thanks for the help! \$\endgroup\$ Sep 8, 2015 at 16:10

1 Answer 1


First, if the controller is running from its own battery, then you can connect its ground and the 24 V ground together (or any one point on each one, but the grounds is usually what you'd connect).

Second, you don't need this device to have amplification on its own. You need to get the signal from one circuit to the other, but the receiving circuit can amplify that as it needs to.

If you really need isolation, then a mechanical relay, solid state relay, or opto-coupler is what you want. If you don't actually need isolation, and it sounds like this is the case, then have a digital signal control a transistor as usual.

  • \$\begingroup\$ Thanks for the thorough answer, connecting the grounds was all I needed to do. Thanks again! \$\endgroup\$ Sep 8, 2015 at 16:08

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