Connecting arduino to power another device

Question

I have an arduino board which I want to use to give power to a device which uses two 1.5V batteries. I think I have to remove the batteries from the device and control the power supply via arduino, but since I have never did this, I'm asking which is the best way to do this.

How would you use arduino to give power to an external, battery powered device?

* Adding details *

I want to power an electro thermoregulator of my house. I have the arduino controlled with a GPRS module, and everything is working fine. The only point left is how to use the arduino to give power to that device.

Answer 1

Since it's battery powered exact voltage is maybe not so important, and you may be able to power it from a 3.3 V supply. Let us know what the device is and we can further advise you.

Anyway, I mention the 3.3 V because the Arduino has a 3.3 V regulator on-board, though it can only supply limited power: a current of 50 mA maximum (Uno). Since you talk about batteries this may be sufficient, but if you need more power I would bypass the Arduino's voltage regulators altogether, and go directly from the Arduino's power input to the 3 V. At high currents and possibly high input voltage a linear regulator will lose much power, so that a switching regulator may be more fit.

So again, tell us what you want to power and we'll tell you more.