Raspberry Pi Pico W not executing main.py when connected with ammeter

Question

I am trying to measure the current flow of a Raspberry Pi Pico W running simple code that blinks the onboard LED saved as 'main.py'. I have verified this code runs when connected to a) my laptop and b) an external breadboard power supply.

When I connected an ammeter (GND on Pico connected to - on PSU, red ammeter probe connected to + on PSU, black ammeter probe connected to VSYS), the only thing I am reading is 0.51 mA when the PSU turns on. I am using a breadboard power supply supplying 3.3V with a 12V DC power supply plugged into the breadboard PSU.

The Pico does not execute main.py. Is there something I am missing? The range on my ammeter has been set to 20 mA, and then 200 mA when that didn't work, to no avail. Thank you!

main.py:

import machine
import time

led = machine.Pin('LED', machine.Pin.OUT)

while True:
    led.on()
    time.sleep(1)
    led.off()
    time.sleep(1)

Answer 1

Maybe the fuse is blown in your ammeter (or you don't have the probes in the right sockets for current measurement).

Try making an independent measurement of current (eg. 1KΩ in series with the ammeter across 5V which should read around 5mA depending on the tolerances and ammeter voltage drop).