Pico Calculator

Pico Calculator

Pico Calculator is a portable mechanical-switches calculator platform powered by the Raspberry Pi Pico. If you are a fan of mechanical keyboards, this is a fun project for you.

The project currently includes two versions:

Pico Calculator

A lightweight and portable version featuring:

• Portable lightweight design
• 1602 I2C LCD
• Beginner-friendly assembly

Pico Calculator Plus

An enhanced desktop-oriented version featuring:

• Larger 1604 I2C LCD display
• 4 utility shortcut function keys:
  • Percentage calculation
  • Percentage difference calculation
  • Customizable currency conversion through firmware (default: USD to BHD)
  • Clear functionality
• Independent power management for LCD and key backlighting
• LED key backlighting (optional)

Parts Needed

Shared Components

Controller

• Raspberry Pi Pico

Power System

• 3.7V Li-ion battery
• TP4056 USB-C Charging Module with Protection
• 5V Boost Converter Module
• 12mm Latching Power Switch with LED light
• JST Connectors / Plugs

Input Components

• Your preferred MX Mechanical Switches
• Keycaps

LCD Components

• I2C LCD Backpack Adapter

Hardware

• M3 screws
• Wiring
• Solder

Pico Calculator

• 1602 16x2 HD44780 LCD Display

Pico Calculator Plus

• 1604 16x4 HD44780 LCD Display

Optional LED Backlight Circuit

• 3mm LEDs for key backlighting
• Resistors
• 2N2222 transistor
• Dedicated boost converter module for the LED circuit
• Transparent legend keycaps

Wiring

LCD (I2C)

• SDA → GP0
• SCL → GP1
• VCC → 5V (from boost converter)
• GND → GND

Switches

All switch inputs are connected directly to available GPIO pins on the Pico and wired to VCC.

The following GPIO pins are used for button inputs:

GP2, GP3, GP4, GP5, GP6, GP7, GP8, GP9, GP10, GP11, GP12, GP13, GP15, GP16, GP17, GP18, GP19, GP20, GP21, GP22, GP26

GPIO assignments are defined in the firmware and can be adjusted depending on enclosure layout to simplify assembly.

Power System

• 3.7V Battery → TP4056 IN+ / IN-
• TP4056 OUT+ → switch → Boost Converter IN+
• TP4056 OUT- → Boost Converter IN-
• Boost 5V OUT → System VCC
• Switch LED → 3.3V → GND
  (make sure your switch includes a built-in resistor or use an external resistor)
• GND → Common ground (all modules)

Optional LED Circuit (Plus Version)

• GP14 → Base of 2N2222 (through resistor)
• Collector → LED cathodes
• Emitter → GND
• LED anodes → 5V via resistors
• Powered by dedicated boost converter rail

Firmware

Install CircuitPython on your Raspberry Pi Pico, then download the required LCD library from the GitHub link provided below.

Finally, choose either calculator.py or calculator-plus.py, rename it to main.py, then copy it to the device root directory.

Two firmware versions are provided:

Pico Calculator

calculator.py

• Standard calculator functionality
• Single press CLS = Backspace
• Double press CLS = Clear all
• LCD power management

Pico Calculator Plus

calculator-plus.py

• Backspace (NumLock) and clear functions (F1)
• Percentage calculation (F2)
• Percentage difference calculation (F3)
• Currency conversion (F4) — customizable via code
• LED + LCD power management

Step-by-Step Installation

1. Install CircuitPython on the Raspberry Pi Pico

2. Download and copy the required LCD library to the /lib folder:

   https://github.com/dhalbert/CircuitPython_LCD/tree/main/lcd

3. Rename the selected Python file (calculator.py or calculator-plus.py) to main.py
4. Copy main.py to the device root
5. Done.

Tips

• Both the LCD and switches are designed for a snug fit inside the enclosure. A small amount of hot glue can be used to secure the LCD if needed.
• It is recommended to first wire the LCD and switches to the Pico, install the firmware, and fully test the calculator before adding the battery and charging circuit.
• The enclosure exposes only a single external port for battery charging. The charging module can be secured using hot glue.
• The Pico is intended to remain inside the enclosure after flashing since no further interaction is normally required.