Vext residual voltage when it's turned Off

#1

Hello. I have the following problem. It’s being hard to use the Vext control. In my case, I’ve tested in two different devices (heltec esp32 LoRa V2) and I got same results. When Vext is On I get 3.3v aproximadetely. When Vext Off, I get 2.4v. I can’t measure 0v from the Vext pin.

The question is that I’m trying to use Vext for a buzzer, but it’s never turns off, cause always there is tension in this Vext pin.

Sorry about my english, hope someone can help me!
Thx

#2

Try this setting.
pinMode(4,INPUT);
pinMode(15,INPUT);

#3

I didn’t understand your suggestion. I’m trying do supply a buzze as an output. I just want to turn on and off the buzzer troughout the Vext 3v3 pin.

#4

Hello, I have absolutely same problem. When I initialize the board like:

Heltec.begin(false, true, true, true, 868E6);
it works as expected (0 V on the Vext pin when Vext off),

but when I initialize like:
Heltec.begin(true, true, true, true, 868E6);
it doesn’t work properly -> (2.4 V on the Vext pin when Vext off).

So the problem is probably caused by OLED / I2C bus.

Does anyone now how to solve this? Thanks

#5

Try with a 1kOhm Pull Down resistor, so the Vext pin can establish the Voltage on that resistance. I was having the same trouble.
I’m using Vext to energize some sensors but when I turned OFF the Vext pin it was still in 2.4[V], but with a 1kOhm resistor working as a pull-down resistance the voltage drops to 0,06[V].

#6

I am having the same problem. Vext is not working. Running this sketch on two different Lora 32 v.2.1:

I get the following results:

Heltec.VextON(); Shows 2.45V
Heltec.VextOFF(); Shows 3.30V

A pull-down resistor did not help.

#8

Try this setting.
pinMode(4,INPUT);
pinMode(15,INPUT);

#9

Adding those two lines did not achieve anything.

I am still seeing between 2.4V and 2.8V when it should be 0.0V.

#10

Does anyone have a solution that makes VEXT work as it is supposed to?

#11

In your code, did you use 21,22 as IIC pins?

#12

21 is not used except for VEXT.
22 is not used.

#13

I had the same problem with AB02S, in my case it was because I still had the OLED display turned on.

Calling display.stop(); made VEXT drop to zero.

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