LED tester

[PEU]

I saw a few days ago in a local shop a led tester which uses a 9v battery and provides a selection of fixed values like: 1.5/3v in 10/20/30/40/50/60/others mA.

Many of the different mA have more than one slot, so brightness comparission is possible.

It uses a female connector like the ones found on ide drive cables.

Is there any circuit for building this available?

thanks

 

[INRETECH]

A really nice LED tester would be:

) 9v Battery
) LM317
) 61 Ohm resistor (or approx)
) Two Clip Leads

It would always apply approx 20ma to the LED

 

[Justintoxicated]

or an LM317T with a switch to select different specified resistor values!

Thinking of making one myself /ubbthreads/images/graemlins/smile.gif

 

[PEU]

could be, but the one I saw had all the currents available at the same time.
As I said, it uses a female ide cable connector for the leds socket.
It would be nice to compare leds. But I don't have the knowledge to build one (may be after MrAl course...:))

cheers

 

[Doug Owen]

I took one of these apart and made a second one for a workmate years ago. It's pretty primative, but effective. There's a few resistors inside, along with the battery and clip. Tie all the socket pins on one side together to say battery minus Each of the sockets opposite gets a resistor to battery plus. Ten pairs of holes, ten resistors. The values (roughly) set the various currents. Differences in Vf mean that red LEDs will be driven harder than white, and they all get dimmer as the battery ages, but for tests and relative output checks it's fine.

Note there's no power switch? You know there's no 'smart stuff' in there.....

Doug Owen

 

[kitelights]

You can buy one from Hosfelt for $7.95.

 

[php_44]

Though it's only happened to me in practice a couple of times - at nine volts it's possible to damage a LED with reverse voltage if you plug it in backwards. The lower voltage red, yellow, orange, and green devices typically have a max reverse voltage spec of 5v. The new blue, green, near UV, cyan, and white LEDs are all generally InGaN - and these also have a reverse voltage spec of 5v.

Typically, most devices are fine connected backwards to 5v, but there may be some that are not. Luxeon and Agilent InGaN LEDs have a reverse protection diode built in - probably because the designers knew the devices could be damaged by either reverse voltage or static electricity.

My LED tester is two CR2032 coin cells with a small series resistor. The 6V is enough to light most any non-arrayed LED and if I connect it backwards there's little chance I'll damage a LED. This is a good way to recycle used coin cells from your photon style lights /ubbthreads/images/graemlins/smile.gif

 

[PEU]

the one I saw is similar to the one @hosfelt, my guess is that it uses a 9v battery but does not supply that voltage.

May be someone suggest me the building blocks of the circuits and I can build one myself.

Using 4 batteries, an lm317 and resistors to limit the current may be?
thanks

 

[INRETECH]

I just have 2x9v Batteries, Resistor, LM317 all wrapped up in tape, with 2 clip leads coming out of it - doesn't draw any current unless you use it - and will always limit the current to 20ma; with 18v - can run any LED or string of LEDs

R=1.25/I