Automatic water filling for keurig coffee maker

Simple microcontroller project that will automatically fill a keurig machine with water when the tank gets low. Based on ATtiny84 microcontroller, uses 3 I/O pins

• PA0 - analog input from eTape liquid level sensor to measure water level
• PB0 - output to 2 WS2818 RGB leds to indicate status
• PB1 - connected to Power MOSFET that turns on a water solenoid to fill the tank

LED colour indications

• Blue - tank is full
• Green - tank is filling up
• Yellow - tank is filling up, but is unexpectedly low
• Red - an error occurred, or the tank is really low/dry

Error Conditions

• tank is really low or dry
• tank has been filling up for more than 2 minutes

Watchdog timer

• software has a watch dog timer that will reset the microcontroller

Programming (Makefile options)

• the Makefile is set up to program the board via a bus pirate connected to the ATtiny84 as a standard AVR ISP port (6pin)

Sofware serial debug

• includes a simple software serial debug, that allows printf to output strings to a bus pirate connected to the ISP.

Note: The microcontroller is powered by a 5V adapter, the solenoid requires 12V, so a buck converter to used to supply the 12V for the solenoid only. The 20K resistor connected between the gate and source of the MOSFET is used to drain an residual capacitance of the MOSFET if the microcontroller output is in an Hi-Z state, thus turning off the solenoid. Any value for this resistor should do from 20K to 100k. The flywheel diode protects the MOSFET from any induction coil induced current when it shuts off, any general purpose diode will do that has a good rating as shown.

Details of the hardware

Basically I built a small plexiglass platform on top of the keurig filter in the tank. Inside the filter is the 8" eTape liquid level sensor. On the platform you'll see the 12V water valve solenoid connected to the water line via a standard ice-cube maker plastic 1/4" line. You can see the controller board beside the solenoid with the LEDs blue.

Behind the microcontroller board is a 5V to 12V buck convertor to provide the power for the solenoid.

On the microcontroller board between the Power MOSFET and the ATtiny84 is the 6 pin ISP connector. I use a Bus Pirate to program the microcontroller when running the Makefile. Also, I can minicom into the buspirate and put it in RAW UART mode to receive the printf statements in the code while debugging.