Is it possible to use the RTC alarm signal on the tamper pin in order to turn on a transistor or maybe hold that value in a D flip flop?

[HAbay.1]

I've been doing a lot of research concerning Low power modes for the stm32 bluepill and I was wondering if i could power my board through VDD and execute a code through it and then right after going into sleep mode I would use a switch to only power the board through Vbat to save power , but the problem here is that the alarm wake up for the rtc won't be able to wake the board up from Vbat so my question is: is there a way to say store that rising edge from the rtc tamper pin and use it to switch back from Vbat to vdd?

[Peter BENSCH · Accepted solution]

Blue pill is now very often populated with clones that do not behave identically to the origina STM32F103C8T6l. So first you should check whether there is a clone or the original F103 on the Blue pill.

The F103 can be operated in stand-by mode and would then only draw approx. 2µA at VDD and 1.4µA µA at VBAT.

Does your external circuit need less current than the above mentioned 2µA to switch off VDD and to detect a switch-on process?

If you really want to save power, you should therefore look at more modern MCUs that are significantly more power efficient, e.g. the STM32L0, STM32L4 or STM32L4+.

Regards

/Peter