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).



Comments

Post a Comment

Popular posts from this blog

Component tester with STM32 : Part 1 ADC, Resistor

Image
I was always  fascinated by the so call "transistor testers" that identify and report pin out, features of pretty much whatever you throw at it. They are based on Atmel 328p chip, the same as arduino nano. So why not do the same thing with a STM32/Bluepill ? The STM32 is faster, has a better ADC accuracy, more memory, can do float etc... and is not more expensive. Warning : I'm doing this for fun & to learn, it might contain error & plain misunderstanding So, i watched a couple of video on the general principle on how they work. This is not a "port" but a rewrite from ~ scratch. When something is weird, i check what the original one does for comparison. Measuring resistance So first thing first :  Resistance & Capacitance. These 2 will unlock the other ones. So how do we measure resistance ? What we do is a resistor divider with a know resistance value: Measure = Vcc*(RtoTest/(RtoTest+Rknown)) As far as the ADC goes, it means ADC=
Read more

Fixing the INA3221

Image
It 's not too complicated to change the board we have seen  previously . You 'll need to cut some tracks, i did it with a dremel and i'm not very handy, so you'll do better. Red =Cut tracks Blue = Add wire 1- You'll need to separate the bottom connector from the ground, cut the 3 connectors BOTH SIDES. 2- Remove the small red area below the middle resistor to isolate each channels from each other Last, connect right side of each connector to the now isolated pad. Mine looks like this after the operation (ugly i know): Be wary of the small track on the left connector that leads to the left side of channel3 resistor. I cut it while isolating the right pad. Now it works, we can go back to the charger.
Read more

INA3221, weird wiring

Image
Continuing my "smart" battery charger, i've finally received the INA3221 module. It is the purple one you can find on ebay for ~ 5 bucks I soldered a couple of pins to be able to connect it so that i could test it and something immediately caught my attention. It is supposed to be a high side current/voltage sensor, typically in a setup like that : So you can measure the voltage supplied to the load, and the current going through it. Now, let's have a look at the module, look at the top of the following pic, where the sense connectors are. CH3/GND/CH2/GND/CH1/GND ? Wait ? What ? Yes, all the IN- pins are connected to ground, so it is a bottom current only sensor. Additionally, the - side of the shunts are ALSO connected to the ground, no only the connectors. The actual layout is like that : That raises two problems :  The voltage is meaningless as we are only measuring Current x ShuntValue, not the supply volt
Read more