Experiences with CR2032 battery backup?

Jan_dM · 2019-12-19 11:43:00 UTC

Thank you rickkas7; this works fine.

Jan_dM · 2020-01-10 12:37:52 UTC

Hi rickkas7,
A month or so ago you suggested to use your utility to read the VBAT from a Photon, and that was very helpfull for the application that I was working on at that time.

Now I have another application, where I am not interested in reading VBAT, but I sure would like to read the internal sensor temperature. However in that application I do not have an unused input pin available. Is there a possibility to read the internal temperature without the need for an unused pin???

peekay123 · 2020-01-10 17:35:47 UTC

@Jan_dM, if you look back on @rickkas7’s utility, he clearly shows code for reading the internal temperature. However, this only applies to STM32F205 based devices - Photon and Electron.

Jan_dM · 2020-01-10 17:58:36 UTC

That’s true, but as you can see it uses a global object photonVBAT (A7, 6.54, 943) in which A7 refers to an unused input. And that is exactly my issue: in my application I have no unused inputs.
So my question is: is there a way to read the temperature in another way (i.e. without the need for an unused input)

Jan_dM · 2020-01-22 18:33:01 UTC

peekay123 can you please comment on my reply to your reaction?

peekay123 · 2020-01-22 19:57:30 UTC

@Jan_dM, @rickkas7’s approach is the only one. However, he uses a “spare” analog input as a “trick” to get around some issues with getting accurate readings. @rickkas7, did you test NOT using an analogRead() and doing two consecutive reads instead?

rickkas7 · 2020-01-22 20:30:50 UTC

The spare pin doesn’t actually have to be an unused analog input. It can be a pin that you are using as an analog input if you do one extra step. Say you’re using pins A0 and A1 for analog inputs and you don’t have any other spare pins.

Set the photon-vbat spare pin to A0. Since it’s already an analog input it will be fine. However, after reading the battery or temperature, also analogRead(A1). This is necessary because you need to read a different pin in order for device OS to reset all of the necessary settings. Using a spare pin assures it’s always a different pin, but reading two used pins also works.

github.com

rickkas7/photon-vbat/blob/master/src/photon-vbat.cpp#L103




	ADC_ClearFlag(ADC1, ADC_FLAG_EOC);


	ADC_Cmd(ADC1, DISABLE);


	// This is not really desirable, but system firmware only sets these setting once,
	// and we override some settings, which will break analogRead()
	// Code from adc_hal.c:
	restoreSystemSettings();


	// We need to read a pin other than the one that the actual code is using because
	// system firmware doesn't reset all of the settings if you read the same pin you
	// last read and you'll get inaccurate readings.
	analogRead(sparePin);


	return value;
}




void PhotonVBAT::restoreSystemSettings() {

Jan_dM · 2020-01-23 14:06:46 UTC

Thank you rickkas7; I will try this next week.