Charging LED wiring help

[VashTS]

I cannot figure out how to wire this up...

I got a + and - from the battery to the + and - of the usb port. I want an LED to come on when its plugged in and just simply stay on until unplugged, nothing too fancy.

I just cannot think how to do it. Any ideas? maybe this diagram works?

This did it! yeah.

 

[FAST6191]

So I assume the obvious step of wiring the LED (plus any Voltage and current control) in parallel with the USB does not work. I guess if the battery/voltage potential turns around when things are unplugged and in turn powers the LED.

If the above is true then the following is unlikely and I know you said you wanted to keep it simple, however does the battery have any kind of proper charge regulator? Regulators will often have an indicator pin that you can tap (or wire into a transistor).

Anyway ignoring the charge regulator option then find a suitable diode*, put it so charge can only flow from the USB and into the device and then put the LED (and its stuff) such that it can only be powered by the USB (in parallel with it having a tap right off the USB and before the diode takes effect). You may also wish to measure the leakage current (measure current flow from the battery with and without the LED attached, I do not imagine it will be much but it will be more than zero.

*most modern ones will probably do, I am not sure they even make normal diodes that break down in USB range. Edit. They do but they seem to mainly be surface mount Schottky diodes so you should be good.

 

[VashTS]

i think i solved it. im going to put a resistor on the LED + leg. so normally 3.7v are flowing through it, resistance will lessen that causing it to not light up. plug in 5v and bam LED lights up.

I think it should work, but I tend to mess this stuff up lol. Worst that happens is i blow $2.

well that was an epic fail. i guess i don't understand how resistance works?

i grabbed a 10ohm resistor thinking thats would work but nerp. tried 100, 1k and 10k.

10k made the light not come on at all.

grrrrrr..anyone else got any ideas?

So I assume the obvious step of wiring the LED (plus any Voltage and current control) in parallel with the USB does not work. I guess if the battery/voltage potential turns around when things are unplugged and in turn powers the LED.

If the above is true then the following is unlikely and I know you said you wanted to keep it simple, however does the battery have any kind of proper charge regulator? Regulators will often have an indicator pin that you can tap (or wire into a transistor).

Anyway ignoring the charge regulator option then find a suitable diode*, put it so charge can only flow from the USB and into the device and then put the LED (and its stuff) such that it can only be powered by the USB (in parallel with it having a tap right off the USB and before the diode takes effect). You may also wish to measure the leakage current (measure current flow from the battery with and without the LED attached, I do not imagine it will be much but it will be more than zero.

*most modern ones will probably do, I am not sure they even make normal diodes that break down in USB range. Edit. They do but they seem to mainly be surface mount Schottky diodes so you should be good.

you lost me here fast.

i get diodes (a tiny bit), they allow current to flow in one direction. im not sure what you mean here...so

USB + -> diode -> led -> battery +? ive got some 1n914 switching diodes wonder if they will work?

edit: see the first post, it worked! yay!

 

[kevinskyman]

sorry, I can't help you.