this post was submitted on 06 Feb 2024
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A Raspberry Pi Pico would be sufficient for this. It uses the RP2040, which is comparable to the ESP32, minus the WiFi.
Actually not really. The pi pico has no functional, good low power states currently developed. That is essential for a mobile device. A pi pico would simply drain the battery in sleep mode very quickly.
Tons of MCUs could do the job. Some STMs would also be good for it. The pi pico is more focused at non-mobile applications though at the moment like a very cheap general MCU for things that are USB powered or mains powered.
For something like this, you would use the RP2040 chip rather than the whole Pi Pico module. The RP2040 uses 180µA in its lowest power sleep mode and the flash and regulator will use a few more microamps. The battery would still last for over a year in standby. Of course it could just be turned off when not in use. Without an operating system, the boot time should only be a fraction of a second.
The ESP32 uses 800µA in sleep mode if you want to retain the memory contents or 10µA with only the RTC memory retained.
A low power STM32 would use orders of magnitude less power in sleep mode than either the RP2040 or ESP32 though.
Yes, I know. I have designed with the RP2040 and 180μA is extremely high power usage for deep sleep mode.
The ESP32 has far more sleep modes than that that each use different power, you are just talking about its light sleep: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/sleep_modes.html
You are comparing the deep sleep of the pi pico to the light sleep of the ESP32 where the coprocessor is still running. The rp2040 light sleep mode consumes 7mA. It is literally orders of magnitude different. https://learn.adafruit.com/deep-sleep-with-circuitpython/rp2040-sleep (they only did light sleep.mode because deep sleep wasn't even available)
As far as the professional chips, they cost on average far more for less and less sleep gains. (A lot of the L series of stm is like 15€ per chip)
You would definitely use deep sleep for this as you would only wake it up to start using it with a button press. Whether they would use light sleep or deep sleep, there is an order of magnitude difference in sleep power consumption.