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.