Program works when plugged into computer, but not when plugged into a battery.

[mogplus88]

Hi All,

I'm confused. I've developed a system (using Micropython) to write an output stream to a pin . It works perfectly when the device is plugged into my computer, but doesn't when it's plugged into a battery. I've confirmed the battery is fully charged and is delivering five volts to the usb plug (it has two 18650 cells). I have also confirmed that the code is executing with the battery by putting some led flashing code in the loop, and the led does flash so the command is definitely being executed. I'm using a logic analyser (cheap Chinses knockoff, but it works) connected to the output pin, and Saleae Logic Analyser 2 to display the output on my PC.

The really confusing thing is, it does it on three different devices. An ESP32 (using the RMT function), a Weact Blackpill (STM32 based) using a timer, and a Pi Pico using a PIO.

What am I doing wrong? What am I missing?

Happy to share code if you think it will help, but it's completely different for all three devices of course. And I couldn't get the backticks to work...

The only other weirdness is that the logic analyser picks up lots of tiny spikes, typically 1us, but sometimes 2us, when it's plugged into the device when it's not powered up. When it's powered by the battery, again there are lots of 1us or 2us spikes, but a lot more of them than when it's not powered. When connected to the PC, whether Thonny is running or not, it works perfectly. No spikes at all, just a beautiful clean signal.

All advice gratefully received.

:-)

[peterhinch]

I assume you have the LA Gnd connected to the device Gnd. The three backticks do work, BTW:

print("The backticks work.")

[mogplus88]

Yes it is. So I tried running it connected to the PC *without * the ground connected, expecting to see nothing or maybe random spikes. However, and I can't quite believe I'm saying this, it worked perfectly. Clean signal. It seems I have a psychic analyser.

Sat here, dazed and confused. Then it occurred to me that the LA is connected to the PC by a usb cable too. Could it be getting its ground from the PC and not the connecting wire? So I checked the wire connecting device ground to LA ground. Broken! Aaaarrrrggghhh!!! Replaced it, and now it runs fine off the battery.

Thank you!

Three backticks. When I clicked the "<>" thing on the menu bar it inserted two. I was assuming I had to put the code in between them. Thanks for the clarification.

;-)

[GitHubsSilverBullet]

And if you have a 'combining' keyboard layout (á à â), then you need to press backticks six times.

[sosi-deadeye]

That's an interesting problem. Why don't you show us your code? Maybe it's not Thonny or the USB port at all. Making an LED blink in a loop is definitely a good idea.

[mogplus88]

Sure. This is the code for the ESP32. Problem solved though, see my reply to @peterhinch above.

# flash the led to indicate prog started
import time, machine
led = machine.Pin(2, machine.Pin.OUT)
for _ in range(10):
    led.toggle()
    time.sleep(1)
led.off()

# actual prog
from esp32 import RMT
from machine import Pin
from time import sleep_ms

rmt = RMT(0, pin=Pin(23), resolution_hz=1_000_000, num_symbols=512, idle_level=False) # pin 23 for NodeMCU Esp32

duration = (1000, 300, 2000, 300) * 4
duration = duration + (7800, 300)

print('enter loop')

while True:
    try:
        rmt.write_pulses(duration, True)
        led.toggle()

    except Exception as e:
        print('Fell over', e)
        rmt.deinit()
        break
    except KeyboardInterrupt:
        print('keyboard interrupt')
        rmt.deinit()
        print('rmt deinitialised')
        break

rmt.deinit()
led.off()
print('program ended')