Before I go about connecting LCD and buttons, I’d like to see how a relay operates the coffee machine.
Here’s a picture of the coffee machine with the bottom plate removed (held by 3 T screws):
The heating element (the pipe in mid-screen) doubles as the carafe warmer. Water are pumped from the tank, heats under the plate and flow back up to drip on the coffee.
Top right there’s a control circuit. When the button (top left) is pressed (and released), a timer chip kicks in and operates the heating element and pump for about 1 minute. The heating element remains on for two hours to keep the coffee warm.
The electrical rating of the entire machine is 800W. Since I’m about to operate the switch for just a second or two, a standard 5VDC relay will do fine.
To keep things simple, I’d like to connect a relay directly to the switch, instead of changing the circuit. Here’s a test-connection:
The relay is a cheap 5V SSR (solid state relay). It cost less than 2$ and
To test the relay, I pulled +5Vand GND from the Arduino supply. Works like a charm. When the relay kicks in, the button closes the circuit and triggers the coffee making process.
Since the digital output pin of Arduino is very low voltage (~1.5V), I’ll connect the relay via a transistor. There are some good resources on the web: