Oscillating output GPIO?

[theinfinityman]

Hello there,

I'm a student, and I recently developed a project using a LOLIN32 development board and everything works perfectly. The device basically provides a 4 bit digital output of a temperature reading, which are connected to LEDs to see at a glance what the binary temperature value is.

I tried to replicate everything this time using a nodeMCU development board, everything works except for the fact that the GPIOs don't provide a steady output but seem to oscillate. Instead of an LED staying on, it blinks.
This happens even when running a simple "LED on" sketch where GPIO is set to constant HIGH.

At first I thought this particular ESP might be set to light sleep mode on a timer by default for some reason. After a bit of testing and using the "esp_sleep_get_wakeup_cause()", this doesn't appear to be the case.

I unfortunately don't have an oscilloscope to test the output, but using a simple multimeter it seems that the outputs don't vary between HIGH and FLOATING, but between HIGH and LOW.

I need to specify that the device doesn't reboot, only the GPIOs seem to be affected, and I noticed this oscillating on the VIN pin as well.

The board is being powered by USB and sketches uploaded using ArduinoIDE.

I have searched all over for a similar issue or possible explanation, but so far nothing fits.

Has anyone else experienced a similar issue? Any possible explanation for why it does this? Any way to fix this issue?

Any help is much appreciated!

[tommeyers]

Sometimes that is what is called "ringing". It can be cause by a circuot point being pulled hign and low at the same time.

Check what is driving that point setting it high an another factor settinv it low.

Tell us what you find.

Internal pullups, ... external ... i dont know.

Post some code a circuit ...

Tom

[theinfinityman]

Hello Tom, thank you for your prompt reply.

I did some testing, and it was hard to find but i eventually did discover an external resistor acting as a pull-up.

I advise anyone having this problem to check everywhere, even a place you might not expect. ESP32 seems to be very sensitive to this.

Thanks again Tom.