Topics created by easytarget

Like @felmue I also did a bit more testing of the low voltage flags, then enabled the charge circuit (and setting the charge voltage via bfvsel to unlimited). The clock has held time ever since.

I'm curious about how long the capacitor can run the clock when fully charged and I have disabled charging again. But my device spends most of it's time on USB power so the duration is hard to measure; so lets try to estimate it :-)

If the frequency out and I2C is disabled (inien = True) the device should typically draw 0.3 µA when on backup battery (table 5 in the datasheet).
The capacitor is possibly a ML414H; 0.07 F.
Table 3 in the datasheet says that the clock oscillator minimum voltage is 1.1v, and the start voltage is VStandby; 3.3v. So we just need to work out the discharge time.

Start with working out the equivalent resistance at 3.3v; R=Voltage/Current = 3.3/0.0000003 = 11000000 = 11 MΩ

Now use an online discharge calculator to do the 'heavy lifting'...
https://3roam.com/capacitor-discharge-time-calculator/
(I like that site; it shows the maths used)

This gives an estimated! time of 845932 seconds; which is ~235 hours, almost ten days. Which seems reasonable for a capacitor backup.

@felmue
Thank you! you are quite right! I hadn't really looked at what was happening properly :-(

The pin needs to be toggled high then low with a ~50ms delay for a full power off, just toggling it high does a full reset (after 1 second). I really wish there was a state diagram (or similar) available for the code in the PMS150G power control MCU.

I've extended my code to do the required pulse similar to your modification, and added a reset_device() method too. Plus relevant notes in the README etc, and done a new release.

[testing shows that the poweroff happens immediately after the first pulse, I'm not sure why they attempt to pulse several times but I guess they are just making sure.. ;-)]

@felmue Thank you for doing the test :-)

I guess this simplifies things for anybody writing a driver; but does prevent people having fun-and-games with under/over clocking the camera module.

I think it also means you cannot 'stop' the camera, which may be problem for extreme power saving. But I suspect the reset pin can be used to halt the module too.