Hardware

This is a learning project. Having no formal education on the subject, I’m learning a lot about PCB design and still have a lot to learn. I’m sure that my designs may have flaws and certainly have a lot of room for improvement. As I learn more, new iterations will be created to improve upon the designs.

The project is composed of the following components:

Main Board

The main board is a custom PCB that contains:

  • A microcontroller. Previous iterations used a Raspberry Pi Pico and a Raspberry Pi Pico 2. The current iteration uses a Sparkfun Pro Micro RP2350.
  • Two MAX3232 chips for converting voltages between RS-232 and TTL.
  • A connector to the DB9 port.
  • An SPI connector to the display.
  • Previous iterations included a QWIIC (I2C) connector. The latest iteration uses a Sparkfun Pro Micro RP2350, which already includes a QWIIC connector.
  • Connectors for a power switch and a power source. A schottky diode is used to block reverse current back into the power source, in case the microcontroller’s USB connector is used concurrently.
The current revision of the main board.
The bottom of an older main board revision.

Keypad

The user interacts with the device through a custom keypad. The keypad has a custom PCB with four Cherry MX keys. The board has QWIIC connections and is powered by an ATTiny84 microcontroller.

Display

A 1.91″ Color OLED display is used to interface with the user. A custom backpack PCB was created to translate the 20 pin header to an SPI connection and expose a reset button.