Maximum Power Point Tracking Solar Powered Computer

Explanation of design

The battery is connected to the IN pin of the INA3221 so that it can measure the current battery voltage. This has to be considered when asking for the charging voltage of the buck converter. It is reduced by the shunt voltage.

Links

3.3 Volts:
https://www.microchip.com/wwwproducts/en/PAC1933#additional-features
IR2104 logic input 3.3 Volt
https://electronics.stackexchange.com/questions/305134/mosfet-half-bridge-driver-not-working

Battery Fuse

Options:
https://forum.electricunicycle.org/topic/6487-almost-started-bms-battery-fire-doesnt-all-bms-have-shortcircuit-protection-on-the-charge-cables/
cheapo PPTC has 1.3 Ohms.
https://www.amazon.com/gp/product/B00X775G34
littelfuse has models with 0.01 Ohm!
https://www.littelfuse.com/products/resettable-ptcs.aspx

Battery protection current limiter

https://electronics.stackexchange.com/questions/262011/mosfet-current-source-current-limiter-request-for-review
https://electronics.stackexchange.com/questions/294061/p-channel-mosfet-inrush-current-limiting

https://www.youtube.com/watch?v=gecjaIV7Fdk&t=166s

https://www.youtube.com/watch?v=C25X2su0sXI

Watchdog

Scenario:
The system is running on battery, the battery voltage is still above the shutdown voltage, but the Espruino software hangs. No data are logged. The relay is still on and the battery is still powering the circuit, but because the Espruino is not monitoring the battery voltage, the battery could be over-discharged.
software solution:
use Espruino watchdog library function
E.enableWatchdog(timeout_in_seconds)
https://www.espruino.com/Reference#E
http://forum.espruino.com/conversations/782/
watchdog circuit:
A 555 timer is set to astable mode, producing a very slow square wave which acts upon the Espruino relay. One period would power cycle the Espruino, unless the Espruino prevents the 555 output from going to low state. The 555 circuit has its own relay to the battery which is turned on by the Espruino upon booting, but does not get turned off while the 555 power cycles the Espruino.
https://www.electronics-tutorials.ws/waveforms/555_timer.html
http://upperbound.com/projects/555-watchdog-timer/