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ESP32 Dev Board 5v connection pin ?

Wp100

Well-Known Member
Hi,

Have a couple of ESP32 Wroom32 38 pin boards, one by Espressif and one known only as Node MCU-32S for programming purposes.

Both run our simple code on a test board, (soldered connections) and uses about 50ma for the tft and some leds , when run from the PCs USB lead.

Not using BT or Wifi.

Connected the test board direct to a known good 1A 5v supply with pin14 GND and pin 19 +5v (often shown on schematics as VIn)

To our surprise the display came on, but the sensors would not read and a bit of checking with the meter revealed some strange results

On the USB supply it showed 4.96v with 4.60v on the AM1117 input pin ( assume thats the series diode drop) and 3.25v on the output / 3.3v pin , all fine.

With the 5v external supply , VIn showed as 4.93v and on the AM1117 input pin as 4.8v, but the output was 3.6 v !!! ( which is the datasheets max value).

Cannot see how that could happen, but it does on both boards, which do have a slighly different component layout.

Tried a 470uf and 100nf across pins 14 and 19 as had read they can have psu problems with heavy current loads, but no effect.

Did try another totally different 3A psu but same results.

If we return to USB power it works fine ??

Seems a very obvious problem , but still rather lost as to whats happening here - any ideas ??!!
 

be80be

Well-Known Member
I had this happen the usb works fine but 5 volt on the vin pin didn't the supply was under 5 volts a bit 4.95 volts
I have some usb supply's that are 5.15 volt they work fine 3.3 volt output the 4.95 volt the output is 3.6 volts

I just figure the regulator is trying to drop out even tho it shouldn't be

But from looking at the vin there is a diode drop but the usb has none
 

Pommie

Well-Known Member
Most Helpful Member
Do you have a supply you can set to 5.6/5.7V to check if it's the diode drop causing the problem?

Mike.
 

Wp100

Well-Known Member
Hi,

Well starting off with a clearer head this morning ...

Both boards appear to have a diode between USB +5v and the AM1117 input pin
The Node MCU-32S board also has one between VIn and the AM1117, but the Espressif board is direct.

Was a bit concerned that my existing PSUs might have some weird fault, so decided to feed the PSU 5v direct to the ESP32 USB connector and the program failed to run correctly, But, the board still had the 470uf across Vin/Gnd from last night, so removed it, and then things ran ok , so that kind of proved the PSU was ok ...?

Then connected the PSU to Vin on the Espressif board but this time at appox 5.72v, but the 3v3 pin then recorded 4.12v , so quicky disconnected.
The Datasheet says the AM1117 needs just a 1v differential, so just cannot see whats happening here.

Even tried connecting the PCs USB +5v to Vin, but that just behaved as with my external PSUs, about 4.92 on Vin and 3.6v on 3v3 pin.

We could just power the board via the USB connector which seems to work ok.

However the controller is used for livestock which need good temperature control, and given the above problem it does leave us a little concerned about its reliability ... :nailbiting:
 

Pommie

Well-Known Member
Most Helpful Member
Can you remove the regulator and supply the board with 3.3V directly? Don't know what it would prove but may give some clues.

Mike.
 

Wp100

Well-Known Member
:facepalm::facepalm::facepalm::facepalm:

Found trhe problem, while we said we connected to Vin and GND pins 19 and 14 respectively, even though the board was wired/soldered weeks ago, we had mistakenly connected the whole circuits GND to Pin 15 which is an IO pin #13 .

When GND placed correctly onto pin 14 then with 5V applied to Vin the output is the correct 3v3 !

The trouble now is , on either Vin or USB power the sensors will not work ( the tft display does) so looks like we might have damaged both boards.
Will have to go back to basic tests and see if the boards are useable. but only for bench testing, too risky for the final build.

Sorry to have mislead you both with our stupid error !!
 

Pommie

Well-Known Member
Most Helpful Member
There are two types of people on this planet, ones that make mistakes like that and liars.

Glad you got it sorted.

Mike.
 

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