OpenDispenser

An Arduino-based controller for a 12V water dispenser with three solenoid valves, toggled on/off via a membrane button array.

Bill of materials

• 1x Arduino Uno
• 3x 12V Solenoid Valve
• 3x NPN Transistor (e.g. TIP120)
• 3x 1N400x Diode (e.g. 1N4001, for back-EMF protection)
• 6x 1K Ohm Resistor
• 1x Membrane button array

Pin mapping

Valve	Button pin (input)	Valve pin (output)
0	13	4
1	12	3
2	11	2

How it works

1. Each button press toggles the corresponding valve on or off
2. The DoubleStateButton class handles debouncing by detecting rising-edge transitions
3. The Valve class manages valve state with an inhibition mechanism to prevent rapid re-triggering
4. The output pin drives the NPN transistor base, which switches the 12V solenoid valve

Project structure

OpenDispenser/
├── OpenDispenser.ino        # Main sketch (3 valves, 10ms loop)
├── Valve.h/cpp              # Valve control with toggle and inhibition logic
├── DoubleStateButton.h/cpp  # Debounced button input handler
└── Circuit/
    ├── OpenDispenserScheme.fzz      # Fritzing project
    └── OpenDispenserScheme_bb.svg   # Breadboard diagram

License

Apache License 2.0 - see LICENSE for details.