Simplest diode tester


Diode mode on a voltmeter is great to test ...... diodes
The main problem is that voltmeters don't get very high in terms of forward/reverse voltage.
Some struggle with voltage higher than ~ 2.5 V, which is not enough for Zeners / Blue Led

So i wanted a cheap, simple, usb powered diode tester. Let's see what was done

The circuit is made of the following main parts :
* 1/2 LM358 :A constant current circuit, the average value is 5 mA. It can be set using the pot. It means the LM358 is enough to deliver such current without a mosfet driver.
* 1/2 LM358 : A differential amplifier to get the tension from the diode to test
* A boost DC/DC converter, to raise the 5v input to 20 V
* One ebay 1$ voltmeter

And it works fine up to ~ 17v. The only issue is that the cheap voltmeter is not very accurate. I  have  tuned it to be accurate around 3v, the further away you get, the larger the error.
But that's good enough for colored leds an low value zeners, which is 90% of my use case.

It's not good enough for Schottky diodes on the other hand.

We'll see later if the accuracy of the voltmeter can be increased.

The circuit :

Inside a 3D printed case, it's not very big  (plenty of the mandatory hot glue).



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