Module for 32 switches

Features

• 32 external switches
• Through-hole mounting
• Pulled up switches (common pole to GND)
• Based on GPIO expanders in the I2C bus

Parts

This PCB is designed to assemble the components yourself using basic tools. Thus, you only need to order the fabrication of the board as the price is much lower.

• MCP23017 in though-hole packaging: x2

• Diodes: x2

  • You can omit the diodes only if you do not need to make use of the WAKE UP pin.
  • Pay attention to the orientation of the diodes.
  • Any Schottky type diode with low forward voltage can be used. The 1N4148 brand is recommended.
  • The positive pole is very close to another soldering pad. Don't worry. It does not matter if you solder them together as they are already connected by a trace.

• Bended male Dupond headers (optional)

  You can also solder the wires directly to the board (recommended).

  • 1x8P (8 pins): x6

Manufacturing

This PCB was designed using Easy EDA Pro. If you want to order a PCB to their prototyping service, take into account that the components are not included in the bill of materials (BOM). You will receive an error message regarding those. To include them, edit the schematic, select a component (grayed out) and set the property "Add into BOM" to "true".

Link to project in Open Source Hardware Labs: https://oshwlab.com/afpineda/module32switches_th. You can one-click order manufacturing from that site.

PCB manufacturing details:

• 2 layers.
• Default physical stacking (there are no choices).
• FR-4 base material (the cheapest, but you may choose another).
• Vias:
  • Minimum hole size is 0.3 mm.
  • Minimum ring diameter is 0.4 mm.
  • Use the cheapest covering.
• Copper weight: 1oz.

Files

• Easy EDA Pro

  Some parts designed but not included in the BOM. Note: you can import this file to KiCAD 9 or later.

• Bill of materials

  Note: not needed unless you want to order components to the manufacturer.

• Pick and place

  Note: not need unless you want to order mounting to to the manufacturer.

• Schematic

• GERBER

Assembly

Pay close attention to the correct orientation of the chips. There is a small circle next to the first pin. This is also marked on the PCB with a square pad, a small dot or a circle. Ensure that these match.

Usage

Only one module can be attached to a DevKit board, as the I2C hardware addresses are fixed to 7 and 0 (decimal). To enable this module in your custom firmware:

void simWheelSetup()
{
    ...
    MCP23017Expander chip1;
    MCP23017Expander chip2;

    // Place the input numbers you want
    // This is just an example
    chip1[MCP23017Pin::GPA0]=0;
    ...
    chip1[MCP23017Pin::GPA7]=7;
    chip1[MCP23017Pin::GPB0]=8;
    ...
    chip1[MCP23017Pin::GPB7]=15;
    ...
    chip2[MCP23017Pin::GPA0]=16;
    ...
    chip2[MCP23017Pin::GPA7]=22;
    chip2[MCP23017Pin::GPB0]=24;
    ...
    chip2[MCP23017Pin::GPB7]=31;
    ...

    // The following two lines are mandatory
    inputs::addMCP23017Expander(chip1,7);
    inputs::addMCP23017Expander(chip2,0);
    ...
}

External wiring

• There are redundant 3V3 and GND terminals. Attach one pair to the power supply, and use the others as you wish. As a suggestion, wire them to the clutch paddle potentiometers.

• Use one or more GND pins as a common pole for all the switches.

• There are two SCL, SDA and WAKE UP pins. Wire one of each to the DevKit board and use the others as a pass-through to other modules.

The pin out should be printed in the back of the board.

I2C bus

The I2C bus is internally pulled up by the DevKit board. Due to wire capacitance, I2C operation could fail. This can occur when long wires are used and several devices are hooked to the bus. In case of need, wire (externally) an additional resistor between these terminals:

• 3V3 and SCL.
• 3V3 and SDA.

Use any impedance between 1K-ohm and 10K-ohm. 2K-ohm is recommended.