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I have a setup where I have a 5V IR receiver and 5V relay board and Arduino Uno.

I am currently powering the Arduino from the PC USB and both the IR receiver and the relay board from the Arduino. And it works fine.

Now I want to know how it would work when I power it with a 9 volts wall adapter. Will the voltage be enough for both the IR receiver and the relay board? And will Arduino work fine?

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The voltage will be fine - as long as you plug it into the DC barrel jack, and don't try to wire directly to the 5V pins. The barrel jack has a voltage regulator on it that will convert 7-12V down to the required 5V.

But there's a second reading that you need to look at, not just voltage. The 9V adapter will also have a current rating expressed in milliamps (mA) or amps (A, which is 1,000 mA). The Arduino needs around 25 mA to do its thing, and your adapters add to the total current - maybe 20 mA each again. So if your adapter only provides 50 mA, it won't be able to provide enough current and the system won't work.

The USB port provides 5V, but it also provides up to 500 mA, which is more than enough for the job. If your wall adapter is 100 mA or above, that should be enough. And unlike voltage, a larger number for current is better - that's its maximum capacity of supply, rather than something that will burn out the equiment!

  • This is the correct answer. As long as you connect the Arduinos properly to the adapter, the voltage is no problem. Amps is what you need, most net adapters for phone charging for example can supply a current of 1A, tablet chargers often go between 2~3A. But as John said: don't fear something with high amperage, it's not like voltage. If anything you'd want the highest amperage you can get, but you can easily settle for 1A. – Len Sep 28 '16 at 8:15
  • I wouldn't go with an adapter that can't deliver less then 500 mA, since it was verified to be working on USB with max 500mA. The relays can draw "quite something" to go on. But without having the data, I would take the worst case scenario/verified (to be working) scenario. – Paul Sep 28 '16 at 13:22
  • But you can indeed try, wouldn't do any harm (but could be unstable). – Paul Sep 28 '16 at 13:23
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If you're connecting the 9V wall adapter to the Power socket of the arduino, then sure its going to work. It can supply both for the IR and relay boards.

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