Hi All. Not sure my question subject accurately describes what I am actually asking, but....what I want to do is this:
I have a circuit that runs off a fixed 5v source. By fixed I mean its a hard wired 5V adapter. What I want to do is have the circuit detect that this 5V source is gone, and it now needs to start running off a battery backup...which is also 5V. This is so when I turn off off the 5V hardwired source, the circuit will now run off the battery input.
Ok cool. How would I set them up in a circuit to use them? I have a thought in mind....but would like to know what somoeone else says before I look like an idiot
Put in a big capacitor, enough to power the Arduino for a few seconds. Now get the Arduino to monitor the voltage via an input pin and switch over to battery if it notices a change.
Ok, so say I do use a big capacitor, how do I tell the Arduino....or in this case a standalone circuit....to use a different power source. Thats the bit I cant figure out.
jscoulter:
Ok, so say I do use a big capacitor, how do I tell the Arduino....or in this case a standalone circuit....to use a different power source. Thats the bit I cant figure out.
That was a bit of a joke...
Connect the battery up via a P-channel "logic level" MOSFET with the 5V supply connected to the gate. The transistor will switch on when the 5V supply drops to zero (helped by your pull-down resistor)
You'll still need a big capacitor though - to keep the Arduino safe during the switchover...
HI. Well I found a solution in the end that works on the breadboard at least It was suggested a couple of posts back, but I wasnt sure what to do...well I knew WHAT to do, just not how to do it.....if you get what I mean :~
I have tested it and its working ok. I can deal with the loss over the diode because then I know I can turn my screen off and just keep the GPS going....an alomost perfect solution