I bought a cheap chinesse water timer with the idea of reimplementing the electronics to add Lora Radio managment so I can turn or or off the valve from a large distance and all running on batteries.
I want to reuse the mechanical design of the product and create my own Arduino based PCB that fits on the plastic enclosure and I want also reuse the latching solenoid inside the device to manipulate the water flow.
While trying to reverse engineer the product I have seen that it's powered by 3xAAA batteries and uses 3.3v logic (I also want to use 3.3v to be as eficient as possible) , the solenoid needs at least 5v to turn or/off so it uses some kind of booster design to charge a 2200uf capacitor and then dump it's load with a very short pulse in one polarity or reversed polarity using a H-Bridge to open or close the valve.
I came up with the following design while using my tester in continuity mode and following the traces on the original product but I can't really understand how it works (suposing I have done it right!)
The product PCB's
a few questions:
1) Does the schematic any sense at all?
2) For my understanding it's using the inductor to boost the voltage, it's conected to the battery and ground with C11 and R14, since it's only needed to charge the capacitor and it's only required maybe only once a day it's not wasting lots of energy from the batteries?
3) What is R6 and D2 used for? to discharge the capacitor of residual energy? taking a look at the PCB D2 is a pin diode, why ?
1.-Following @kutukvpavel excelent answer I have redrawn the schematic using the same convention with my original components for clarity.
2.- D2 is a zener diode actually drawn upside down, I corrected it.