Multiple power sources for Arduino

Hello all, This subject probably been addressed before, but darned if I can find it. Anyway, I have put together a wireless telemetry receiver consisting of an Uno and LCD connected to an APC220 wireless transceiver. Everything works great. Now, as phase 2, I want to set it up such that it runs on an AC transformer when utility power is available, and switches to battery backup when utility power fails. Additionally, I want it to be able to send a signal to the uno that will allow it to switch to a power-saver mode. I have researched mux chips, but am now more confused than ever. Is there a relatively painless way to accomplish this? Thanks in advance!

Gary

A mux chip is the wrong way to go about this.

A couple of diodes would be the simplest solution and adding an opamp to sense the current through a diode would provide a signal for your Arduino.

Linear Technology makes some chips for this purpose and may be the simplest solution.

vaj4088: A mux chip is the wrong way to go about this.

A couple of diodes would be the simplest solution and adding an opamp to sense the current through a diode would provide a signal for your Arduino.

Linear Technology makes some chips for this purpose and may be the simplest solution.

Thanks for the quick answer, it seems op-amps are a recurring theme in my life ATM, LOL

As I am relatively green at this stuff, can you kindly point me to a circuit digram?

@vaj4088,
I found a circuit that should do what I want, using an LTC4412; it even has a pin that goes high when the AC adapter is on, and low when it is off. Thanks for pointing me in the right direction!

I am glad to help.

Since you seem to be able to handle the ThinSOT package anyway, you might consider:

  1. The LTC4411, which avoids the FET.
  2. The LTC4415, which avoids the FET and the diode.

Oh, and by the way: the circuit that you attached omits the pullup resistor that is required on the status output. Of course, if you enable the input pull-up resistor on the Arduino, you will not need the added resistor.

…and none of these need an opamp! :slight_smile: :slight_smile: :slight_smile:

vaj4088: I am glad to help.

Since you seem to be able to handle the ThinSOT package anyway, you might consider:

1) The LTC4411, which avoids the FET. 2) The LTC4415, which avoids the FET and the diode.

Oh, and by the way: the circuit that you attached omits the pullup resistor that is required on the status output. Of course, if you enable the input pull-up resistor on the Arduino, you will not need the added resistor.

...and none of these need an opamp! :) :) :)

Thanks, I'm not thrilled at the packaging, I'd prefer a through-hole design, but one must use what's available. I'll check out the chips when I get a chance. Simple is ALWAYS better.