Port, board and/or hardware

esp32-C3 Mini

Matrix board like this https://www.hobbyelectronica.nl/wp-content/uploads/2021/11/8x8_WS2812_Led_matrix.jpg
with WS2812b Neopixels, all individual Neopixels have decoupling capacitors.

MicroPython version

MicroPython v1.24.1 on 2024-11-29; ESP32C3 module with ESP32C3

Reproduction

When Wifi is enabled and connected, a neopixel matrix (8x8) gives unexpected glitches.
Power and signal levels are checked and ok. (checked with an oscilloscope.)

This bug is the same as in https://github.com/micropython/micropython/issues/8161 however the fix will not work because the esp32-C3 Mini has only one core.

If this bug cannot be solved, I suggest adding a warning in the documentation that Neopixels on eps32 (single core types) cannot be used reliable when Wifi is on and used.

import time
from neopixel import NeoPixel  # Standard lib of MicroPython v1.24.1
from machine import Pin
import config as cfg
import network

wlan = network.WLAN(network.STA_IF)
wlan.active(False)
ap_if = network.WLAN(network.AP_IF)
ap_if.active(False)

if not wlan.active():
    wlan.active(True)
    time.sleep_ms(100)
if not wlan.isconnected():
    wlan.connect(cfg.ssid, cfg.passwd)
while not wlan.isconnected():
    time.sleep_ms(100)
    print('.', end='')

np = NeoPixel(Pin(4, Pin.OUT), 32)  # Use 4 rows of 8 pixels
np.fill((0,0,0))  # All pixels off
np.write()

np[0] = np[8] = (1,0,0)  # Red, lowest intensity
np[16] = np[24] = (0,1,0)    # Green, lowest intensity

while True:
    np.write()
    time.sleep_ms(20)

The configuration of the pixels of this board is as follows:

0  1 . . . . . 6 7
8  9 . . . . . . . 
16 etc.

So the example program above should give

R . . . . . . .
R . . . . . . .
G . . . . . . .
G . . . . . . .

Expected behaviour

First column (0) should be as above and steady

Observed behaviour

Only when Wifi is on and connected, glitches appear like for example:

R . . . . . . .
R . R . . . . .
G . G . . . . .
G . . . . . . .

or

R . . . . . . .
R . . . . . . .
G . G . . . . .
G . G . . . . .

The glitches always appear in column 2 (two pixels away from the first column)
and has the same color as the left one. I have not seen glitches in top row (0)

Additional Information

Conditions:

1. Power supply (both 5 and 3.3Volt) has 100nF ceramic parallel with 470uF capacitors.
2. Input signal of matrix module is within datasheet specs and look clean (Checked with oscilloscope).
3. No long wires.
4. No high currents (average current of the setup is below 50mA)

I checked the (total) time of the pulsetrain on the output of the esp with a oscilloscope, it shows 32 * 24 * 1.25uS = 960uS
This is as expected. However sometimes the pulsetrain is extended an extra 60uS.
This is probably when the glitches appear.

I also did the test with all 64 pixels (total time of pulstrain 1.92mS, column 0 -> RRRRGGGG) then also sometimes the extra 60 uS appear. Also parts of (bottom of) column 0 is copied to column 2 like above.

I have tested this with a few esp32-C3 and a few matrix boards. They all have the same behaviour.
I also tried using machine.bitstream but the same behavior shows up.

Code of Conduct

Yes, I agree