I started by installing an earth wire (green) to the LED bezels – as any conductive surfaces on the exterior of the box should be properly earthed. Next the cathodes of the LEDs were bent together and soldered in place with a ground wire (black). Each anode then got its own signal wire (orange).
Next the navigation buttons received their common ground (black) and individual signal wires (white/grey). Each signal wire not only connects to an input pin on the arduino, but also connects to the 5V rail via a 10k pull-up resistor. This circuitry, however, I will deal with soldered directly on the proto-board.
After this my LCD needed its leads, so I soldered together the connections in the pin header sockets using red for 5V, black for ground and yellow for data lines.
On the back panel the SSRs need their signals and common ground. As the signal that triggers the SSR is physically the same pin that lights the respective LED I chose to use orange for these lines too.
All these various lines then connect each component to the arduino via a shield made from prototyping board. I took strips of pin header and pushed the pins all the way through their black plastic strip so that I could keep the solder side towards the arduino. Unfortunately the second bank of digital connections (data lines 8 to 13) are not aligned with the grid of the proto-board, so they need to sit on their own little board. This is a slightly annoying feature of the way that the arduino has been designed – and the cynic in me wonders if it’s to create a market for people buying prototyping shields!
The main items that live on the circuit board are 5V, 12v and ground buses; the button pull-up resistors; the LCD contrast trim-pot and the buzzer transistor. As a result, none of the circuitry is mind-boggling complex and a custom printed PCB is an unnecessary expense (although it would make for a far quicker job).
Once all this wiring had been completed it was time to flash the arduino and see if it all works. And success!
Currently the LCD, navigation buttons, and LEDs are fully functional. There are header pins for the SSR signal wires to plug into (allowing both halves of the box to split apart) and the transistor for the buzzer needs to go in. My temperature probe has not arrived yet, so that only has some loose wires (purple) awaiting it.