High energy consumption when using machine.lightsleep

[mu88]

Dear community,

As my first MicroPython project, I've connected a Waveshare eInk display with a RP2040 and display some temperature data (see here). It works nicely, so I started digging deeper and bought an USB stick to measure the Raspi's power consumption, which confuses me a little bit.

Here you can find the complete MicroPython code, but the process looks like this:

1. Connect to WiFi
2. Pull new temperature data (via HTTP GET, returns binary data)
3. Update screen with new temperature data
4. Sleep for 5 min via machine.lightsleep(300000)

This code runs in a while loop.

What makes me wonder is that after calling machine.lightsleep, the power consumption is still between 48 and 52 mA. Why is this the case? Do I have to manually turn off the WiFi before calling machine.lightsleep? Or should I forget about the while loop and use machine.deepsleep(300000) so that my MicroPython script runs from the very beginning every 5 min?

[davefes]

The only reason, that I can think of, for using lightsleep on the ESP32 is that you can retain program state, ie pin hold. It is like a pause. Yes, you need to do a sta.active(False)before going to lightsleep and then a sta.active(True) when waking-up.

If you are not wanting to hold any output ports then deepsleep could save you more current. Be aware, if you are using a dev board with a USB to UART chip on it that it sucks current as well.

[robert-hh]

I found an interesting behavior with the Pico W. If I just start it and call machine.lightsleep, the current drops to ~13mA. If I call

import network
wlan=network.WLAN(network.STA_IF)
wlan.deinit()
machine.lightsleep(time)

the current drops to < 1mA. That even valid when WiFi is not used otherwise. With wlan.deinit() the LED turns off, which alone contributes to ~5 mA current.

[davefes]

Right, this is a much better answer! I had noticed that behaviour on the Pico W as well, but somehow tried to relate it to my ESP32 experience.

Does lightsleep on Pico W allow you to hold pins and/or retain program state?

[robert-hh]

The pin state should be retained, and the code state as well. Only the clock freq. is reduced and USB switched off.

[robert-hh]

Supplying negative values to lightsleep(n)/deepsleep(n) will sleep almost forever. It then perform to code path of time.sleep_ms(n).

[davefes]

Thank you for the clarification.