Objective

This faucet has started acting erratic, turning on and off for no reason. The plan is to figure out how the "electronics box" communicates with the sensor and the solenoid and then replace the "electronics box" with our own micro-controller. 

Faucet Specifications

Removing the Electronics Box

Initial Thoughts

Initially I believed that this was a mini USB cable and as such used the USB protocol to communicate from the electronics box to the sensors. 

Upon further inspection, it became clear that this is not a standard USB mini cable. This cable has 10 connectors. 

Original Board

De-potting the Controller

Dislodged Chips

Resistor: 01D - 100K

Capacitor

Board Observations

ATMEL MEGA 328P Microprocessor 

Chips

WE 25C

The WL2801E series is a high accuracy, low noise, high speed, low dropout CMOS Linear regulator with high rippler ejection.

Output Voltage: 2.5v ?????

https://www.alldatasheet.com/datasheet-pdf/view-marking/1140142/WILLSEMI/WL2801E25-5/TR.html

F AC31 SS32

Fairchild Semiconductor Schottky Rectifier

https://www.mouser.ca/datasheet/2/308/1/SS39_D-2320135.pdf

A7W 1n?

DBAMD

6 pin

K38 Y9

50V N-CHANNEL ENHANCEMENT MODE MOSFET

https://www.alldatasheet.com/datasheet-pdf/view-marking/1457389/DIODES/BSS138WQ-7-F.html

Monitoring the Serial Output

We should be able to use an FTDI Interface board to see if the board outputs any debug information. 

Note: this chip is powered by 3.3V

No debug logs outputted.  

JTAG 

We traced the JTAG spots back to the microcontroller and it appears that the JTAG exposes a SPI (Serial Peripheral Interface) interface.

Perhaps for programming the ATMEL chip?

Connector

The cable in question appears to be a mini USB 10 pin cable.

This female 10 pin connector is compatible with the male 5 pin but only uses the top 5 pins (2,4,6,8,10).

Used pins are: 3, 5, 7, 8, and 9.

Since this board is using mostly the bottom pins, we can conclude that this is not a USB connection.

Board Schematic