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Katduino: Part 5 – wiring notes

There’s a been a bit of interest in how I put this amp switcher together and I realised I hadn’t really shared any details about exactly how it’s all wired together so here’s some gutshots and some notes about how it’s all plumbed together.

The guts of the Katduino pedal
The front of the switch control board
The back of the switch control board
The relay board wired to the stereo socket

I’m using a standard Boss style 2.1mm DC socket so wiring this is straight forward – the positive terminal goes to the Raw V+ pin on the Arduino and the ground terminal goes to a GND pin.

The LCD screen is wired in with VCC and GND on the screen going to VCC and GND pins on the Arduino. The SDA and SCL screen pins go to A4 and A5 on the Arduino although you should double check the right pins for your screen and Arduino model. I also used i2c scanner programme to make sure I had the right HEX address for the screen.

// Set up the LCD
LiquidCrystal_I2C lcd(0x27, 16, 2);

By switch vero board takes its voltage straight from a VCC pin on the Arduino and is grounded using a GND pin. Each footswitch is wired to the respective input pin on the Arduino as well.

// Define footswitch pins
#define S1 10
#define S2 11
#define S3 12
#define S4 13

The relay board connects to a couple of places and you’ll probably want to experiment here to make sure you get this right. If you get it wrong you’ll end up with a mismatch between the channel the Arduino thinks your amp is on and the actual channel.

The relay takes its voltage from a VCC pin on the Arduino and its GND connects to a spare GND pin. The two input terminals go to the correct Arduino pins that are specified in the code.

// Define the relay pins
#define CH1 2
#define CH2 3

Finally the relay board needs to connect to the 6.35mm stereo socket that I’ll be using for the TRS cable that runs between the pedal and the amp. For my relay, I have the following connections:

  • NO1 – ring (the central part of the jack)
  • COM1 – sleeve (part of the jack furthest from the tip)
  • NC1 – no connection
  • NO2 – tip
  • COM2 – sleeve (part of the jack furthest from the tip)
  • NC2 – no connection
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