ok, ive been working on this LED tester, and all it is is some batteries, a rheostat, and some alligator clips to clip the led to. now, i need to make some sort of scale so that i know how much resistance there is. here is a pic of it. so as you can see i have a arm on it so that it points to the resistance. im not sure how to make the scale because im not sure how to find out how much resistance it has.
A problem with any led tester is allowing for the user to connect the led the wrong way round. 9V applied backwards will kill a led; I was that soldier. Best idiot-proof circuit I've seen is this one; a bit less idiot-proof but simpler would be a 317 constant-current source set for about 10mA running off a 6V battery. See the 317 datasheet.
its simpler than building a fairly complex circuit board whichs parts would cost me money, and if someone else breaks one of my LEDs, they owe me a new one. simple as that.
If you haven't included it already, it might be a good idea to add a 68R resistor in series with one of the leads to the LED so that even if the variable resistor is set to 0R, you won't damage your LED.
