Hi,

I have a wire that will output either a positive or negative voltage onto an LED, depending on the input. I need a way to change the negative output into positive voltage of the same magnitude (or as close as possible) so that it can power the LED. The circuit needs to be as small as possible. Any suggestions?

 

Hello,

You could use a fullwave rectifier (bridgecel) in front of the led.
Here demonstrated with a sinawave input signal.
http://www.falstad.com/circuit/e-fullrect.html
Do mind the restistor to limit the led current.

Greeting,
Bertus

 

Use two LEDs, connected in opposite polarity.
[eta]
See attached

 

Hello,

When you are using sgtwookies drawing you could also use a 2 pin duo-led.
These duo-leds consist of two leds in different colors, connected opposite.
In this way you can see if the voltage is positive or negative.

See link (in dutch but the picture is clear).

http://www.leds-buy.nl/pin-duo-led-groenrood-graden-5mm-p-84.html

Greetings,
Bertus

 

Bertus,
DuoLEDs will not work in this application. They have a common anode or a common cathode, depending upon the device; they have three leads.

They may exist, but I haven't seen a trademark DuoLED where they are connected anode-cathode and cathode-anode.

Radio Shack DOES sell a red/green bipolar LED that only has two leads, which would work just fine in this application. Link:
http://www.radioshack.com/product/i...032058.2032233.2032298&pg=2&parentPage=family

 

Hello,

In the link provided there are leds with anode connected to the others led kathode.

There are green/red and green/orange available over there in 3 and 3 mm.

Greetings,
Bertus