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Author Topic: LED Tester (KEMO M087)  (Read 3426 times)
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metal
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« on: December 24, 2012, 12:35:18 00:35 »

It is simple, any one knows how it works?
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pickit2
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« Reply #1 on: December 24, 2012, 01:30:10 01:30 »

http://www.ebay.co.uk/itm/251111198223
looks like it is voltage/current supply, no meters, you look to see if led is lit...
note: In order to facilitate selection of LED's of equal brightness, there have been placed two test sockets with the same currents (10mA) side by side.

one question is, what if you need IR leds testing?
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« Reply #2 on: December 24, 2012, 01:33:43 01:33 »

IR LEDs? Plug them into the tester, then look at them with your camera phone or digital camera to see if they're lit.
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« Reply #3 on: December 25, 2012, 12:15:45 00:15 »

IR LEDs? Plug them into the tester, then look at them with your camera phone or digital camera to see if they're lit.

Yes I know that, I was asking if using the Kemo Kit.
I use a Bleeptone 12V 1kHz (4713000/02) with a 9V battery, meter test leads, it will show A&K of LED, also test 7 seg LEDS, the leds light and sound the buzzer.
will also test diodes and transistor junctions. using the buzzer no need to look at a meter
http://www.soemtron.org/downloads/disposals/minileeptone525.pdf
« Last Edit: December 25, 2012, 12:18:59 00:18 by pickit2 » Logged

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metal
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« Reply #4 on: December 25, 2012, 01:05:12 01:05 »

I need to understand how it generates 1mA current source, that's not an easy task. Also, what sort of circuitry that could fit inside such a small box!?
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« Reply #5 on: December 25, 2012, 03:40:23 03:40 »

I need to understand how it generates 1mA current source, that's not an easy task. Also, what sort of circuitry that could fit inside such a small box!?
Inside, you may find a reference LED and a simple current mirror for each channel. It also may be not very accurate when it says 1mA or even 0,5mA. Just a guess.

EDIT: found this, sorry for it beeing in german...: http://www.elektronik-kompendium.de/public/schaerer/bilder/currop06.gif  .but I think in the KEMO device there will be something way simpler and less accurare, more like this: http://tinyurl.com/d9af7gt
« Last Edit: December 25, 2012, 04:11:01 04:11 by dotm » Logged
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« Reply #6 on: December 25, 2012, 12:07:01 12:07 »

It is even simpler ...
the CE marking on such product is misleading and stands for China export




the circuit uses no power switch so it has to be open when the LED is not connected and since it is not going to be used for long time, so temp. coefficient is not an issue, the Chinese will use a Basic CCR circuit with 2 transistor 2 cent each and 2 resistor with a cheap 6LR61 9V battery as it will be active for several seconds, the main cost will be in the enclosure. Smiley   

attached is the ISIS expected circuit for the 1mA CCR and you can alter the fixed resistor for other currents.
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« Reply #7 on: December 25, 2012, 06:13:17 18:13 »

dotm:
This circuit has the opamp connected to Vcc.

Faros:
This is what I expected, seems there is no escap doing this the old way :- )
This one is affected by battery voltage change.

I think the one attached is better regardless of battery voltage, but has the zener passing current all the time.

Posted on: December 25, 2012, 07:23:08 19:23 - Automerged

I think I solved the zener being connected all the time! Look at 'CCS 2.dsn'
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