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Mysterious voltage drop when ESP32 board is connected

Posted: Thu Nov 23, 2017 5:43 pm
by Albert
I'm powering my Node MCU ESP32 board by implementing a voltage divider on a 12V supply and then feeding to a 7805 regulator and using the output of the regulator to power the board.

When i connect the output of the regulator to the board, there is a mysterious voltage drop from 8V to about 4V at the voltage divider. This voltage is in turn fed to the regulator so the output of the regulator is now about 2.5V instead of 5V.

I'm using a 330 ohm resistor(R1) and 680 ohm resistor(R2) for the voltage divider with a supply voltage of about 12V. Also im powering the board from the 5V breakout pin of the board.

Anyone please help me understand what is going on?? :x

Albert.

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 5:53 pm
by loboris
Nothing Mysterious:
Ohm's law
or this one

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 6:10 pm
by Albert
Loboris,

I dont understand this. Why should i get 4V at the voltage divider instead of 8V??

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 6:30 pm
by krzychb
Hi Albert ,
Check https://www.youtube.com/watch?v=XxLKfAZrhbM
This is among my favourite from Afrotechmods :D
For this particular issue the explanation is at 2:08

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 7:05 pm
by Albert
Thanks krzychb. This is definitely my problem. Afrotechmods has just explained the problem but now i wonder what the solution is!
Here is my circuit. How can i get 5V to my ESP32 ??
20171123_183227.jpg
20171123_183227.jpg (1.67 MiB) Viewed 2305 times

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 7:46 pm
by loboris
Albert wrote:Thanks krzychb. This is definitely my problem. Afrotechmods has just explained the problem but now i wonder what the solution is!
Here is my circuit. How can i get 5V to my ESP32 ??
Just connect +12V directly to the 7805 input. If it gets too hot, mount the small heatsink.
If you have problems understanding basic electronics, I would recommend to simply use 5V power adaptor.

Re: MYSTERIOUS VOLTAGE DROP WHEN ESP32 BOARD IS CONNECTED

Posted: Thu Nov 23, 2017 7:51 pm
by krzychb
Depending on particular producer of 7805 regulator, the maximum DC input voltage is either 25 or 35V - http://www.ti.com/lit/ds/symlink/lm340.pdf

Therefore you can connect 12V directly to the "In" of 7805 shown on your schematic

Re: Mysterious voltage drop when ESP32 board is connected

Posted: Thu Nov 23, 2017 10:57 pm
by ESP_Angus
Hi Albert,

I've edited your post title to not use ALL CAPS. Please do not use ALL CAPS when posting on the forum.

Angus

Re: Mysterious voltage drop when ESP32 board is connected

Posted: Fri Nov 24, 2017 3:49 am
by Albert
Thanks and sorry for that.

Albert

Re: Mysterious voltage drop when ESP32 board is connected

Posted: Fri Nov 24, 2017 4:08 am
by Albert
Hey krzychb,

Im very grateful for the help. I was actually worried about the heat because i do not have much space for a heat sink but i realised that the heat dissipation will be 1.06 W so i dont know if i will need a heatsink if i connect the 12V directly.

Im powering the ESP32 from the circuit board of a controller so a 5V adapter will not be suitable.

Albert