Author Topic: Huge voltage drop on diodes  (Read 641 times)

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Offline fpazos

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Huge voltage drop on diodes
« on: Sun, 23 May 2021, 05:58:58 »
Hi guys!!

First time in a long time coming with problems.

As you can appreciate, I'm currently working on a fully 3d printed RGB hot swap numpad.

I have noticed that there is a huge voltage drop on the diodes. The signal only travels through 2 diodes.
I tried with a custom tester that consists on an STM32 with a led, through one diode you can appreciate that it shines less but when crossing through 2 it shines with the minimum intensity.

I don't know if being Chinese diodes could matter as these would be the only Chinese components on which I have found problems.

https://drive.google.com/file/d/1EpWkWGGG9EJz2opKAKIV8-Lenn_FrkQ0/view?usp=sharing

Why I'm the only person experiencing this problem, as these seem to work fine following the comments: https://es.aliexpress.com/item/32465250573.html?spm=a2g0s.9042311.0.0.274263c0dmtrEL

Could I be missing something or these are just ****ty diodes? Will these fit? (description in English) https://www.electronicaembajadores.com/es/Productos/Detalle/SMDI1N4148/semiconductores/diodos-excepto-leds/1n4148-diodo-rectificador-100-v-0-2-a-do35

I was quite happy as I found a quite easy way of creating a complex handwired pcb.

Thank you for your help!!
« Last Edit: Sun, 23 May 2021, 06:00:56 by fpazos »
 

Offline suicidal_orange

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Re: Huge voltage drop on diodes
« Reply #1 on: Sun, 23 May 2021, 06:23:55 »
If the diodes in the first pic are being used in a switch matrix they are not connected as they should be - they are in series not parallel.  See this pic by fknraiden:


When connected properly the signal never goes through 2 diodes so it probably doesn't matter that they have high resistance.

Most diodes are going to be made in China (like most everything!) so that's certainly not the problem, though of course can be faulty examples of everything so you could have bad ones.
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Offline piit79

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Re: Huge voltage drop on diodes
« Reply #2 on: Sun, 23 May 2021, 06:37:19 »
Hey, I'm on mobile so didn't check any linked resources, but it sounds like you are trying to put the LEDs in series. The typical voltage drop on a LED is between 1.7 and 3.3 V depending on the colour, so it's normal that you cannot put more than a few LEDs in series on 5 V.

The LEDs need to be wired in parallel, each with its resistor. They need to be switched on/of using a MOSFET as they will consume a few hundred mA depending on the desired brightness.

RGB diodes are essentially 3 diodes in one package - red, green and blue. You would need to control the brightness of each colour independently to get the desired colour.

If I were you I would use RGB modules with a built-in driver, like WS2812B. They only need one data pin that allows sending serial data to each module and set its colour/brightness independently.

Hope that helps at least a bit :)

Offline Findecanor

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Re: Huge voltage drop on diodes
« Reply #3 on: Sun, 23 May 2021, 07:01:12 »
The LEDs look like they could be WS2812B already, and connected right. ;) It's the diodes in the switch matrix that are connected wrong.

The rows and columns in the matrix should be uninterrupted, with a <switch and a diode> in each junction.
The switch and diode should be in series only in-between its row and column. The order of the switch and diode in series do not matter however, just as long as the diode points in the right direction.
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Offline nevin

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Re: Huge voltage drop on diodes
« Reply #4 on: Sun, 23 May 2021, 07:42:40 »
i'm guessing your talking about the led brightness (leds are diodes as well, the light emitting kind)
- make sure the leds have drivers or you will need some booster circuit (mosfet, transistor, etc)
- make sure you're using a PWM pin on the controller (usually only a couple PWM pins on a controller, pick one that supports PWM)
- my guess is the leds don't have drivers and you'll need a booster circuit to drive enough current to the leds.

diodes look ok to me... they just have them in the columns instead of the rows, and that can be switched in firmware.
- and yes, 1N4148 diodes are what is typically used in the switch matrix.
« Last Edit: Sun, 23 May 2021, 07:45:16 by nevin »
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Offline suicidal_orange

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Re: Huge voltage drop on diodes
« Reply #5 on: Sun, 23 May 2021, 12:24:29 »
diodes look ok to me... they just have them in the columns instead of the rows, and that can be switched in firmware.
I'm stupid at the moment so took a second look before deleting my wrong advice above but no, they are definitely wrong.  Row or column is indeed irrelevant but you can't go from one end of one diode into the other of all that come before it, all the same ends need to be connected together.
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Offline fpazos

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Re: Huge voltage drop on diodes
« Reply #6 on: Sun, 23 May 2021, 16:24:01 »
If the diodes in the first pic are being used in a switch matrix they are not connected as they should be - they are in series not parallel.  See this pic by fknraiden:
Show Image


When connected properly the signal never goes through 2 diodes so it probably doesn't matter that they have high resistance.

Most diodes are going to be made in China (like most everything!) so that's certainly not the problem, though of course can be faulty examples of everything so you could have bad ones.
I just felt very stupid hahaha. I just improvised the wiring and I had the impression that I was missing something.

Thank you!!!
« Last Edit: Sun, 23 May 2021, 16:34:56 by fpazos »
 

Offline fpazos

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Re: Huge voltage drop on diodes
« Reply #7 on: Sun, 23 May 2021, 16:32:16 »
Hey, I'm on mobile so didn't check any linked resources, but it sounds like you are trying to put the LEDs in series. The typical voltage drop on a LED is between 1.7 and 3.3 V depending on the colour, so it's normal that you cannot put more than a few LEDs in series on 5 V.

The LEDs need to be wired in parallel, each with its resistor. They need to be switched on/of using a MOSFET as they will consume a few hundred mA depending on the desired brightness.

RGB diodes are essentially 3 diodes in one package - red, green and blue. You would need to control the brightness of each colour independently to get the desired colour.

If I were you I would use RGB modules with a built-in driver, like WS2812B. They only need one data pin that allows sending serial data to each module and set its colour/brightness independently.

Hope that helps at least a bit :)
Thank you!! Leds are working fine!! I'm using addressable 5050 leds attached to a mini pcb from aliexpress too. Nice components for hadwiring.
The LEDs look like they could be WS2812B already, and connected right. ;) It's the diodes in the switch matrix that are connected wrong.

The rows and columns in the matrix should be uninterrupted, with a <switch and a diode> in each junction.
The switch and diode should be in series only in-between its row and column. The order of the switch and diode in series do not matter however, just as long as the diode points in the right direction.
Yes. That's true!! Rookie mistake even when I'm not that rookie. Thank you for your help!!

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Offline nevin

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Re: Huge voltage drop on diodes
« Reply #8 on: Sun, 23 May 2021, 18:45:04 »
Crud. You're right. I missed that at first.
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Offline fpazos

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Re: Huge voltage drop on diodes
« Reply #9 on: Mon, 24 May 2021, 01:27:18 »
Crud. You're right. I missed that at first.
Thank you for your help anyway!!!

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Offline fpazos

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Re: Huge voltage drop on diodes
« Reply #10 on: Mon, 24 May 2021, 01:35:03 »
Thank you all for your time and help.
It is awesome to be part of this great community. Maybe the best out there.
I experienced some problems with my 3D printer but I hope to solve them sometime after summer and be uploading a big post with all my latest works.