I'm trying to power a Nano and a sim900 from a battery pack that supplies 5v. I've powered both (nano and sim900) separately from the pack just fine. Now I need to power both of them from the same battery pack.
I've read the USB connector needs to be supplied with 5v. Also that the Vin must be supplied with something higher than 5v, such as 7-12V because of a dropout voltage of about 2v, same as the barrel jack. Finally that I could also feed 5v to the 5v pin even though it's designed to output 5v instead of take in 5v.
So it seems better for me to use a usb cable with clipped cables wired to the output of the battery pack than to risk inputting 5v through the intended 5v-output pin.
Any thoughts? Suggestions?
That what I have done on my Sim900 project, plus adding a small battery backup, so a mains power fail message can be sent out.
Feeding in via the Vcc would seem possible, but it really depends on the onboard 5v regulator and if its output can withstand this external 5v, a debateable point, plus many clone boards use a mix a regulator types/quality, so think the USB socket is the safer option.
Thanks rick. So I cut up a usb cable with the mini-B type which is what the nano takes. It has 4 cables:
red, black, green and white
I want to make sure the red and black would be pos and neg. But I would need a mini-B usb type receptacle on the other side that I could test with a tester. I dont have one. I took apart an old RC helicopter that had one but first off, I bent the heck out of the receptacle and second, it has 5 connectors inside vs the 4 cables I have and the leads going onto the pcb board it comes on are pretty small to get a tester lead in there.
So Im just wondering if there is a better way before I go take apart something else
Plug the cable into your Nano. Use a meter to measure for conductivity from the Nano Gnd to the various wires, and from VUSB to the wires. VUSB is pin5 of the USB connector, or the Anode of D1. Gnd is pin1 of the USB connector.