displayhatmini-lite 0.1.5

Lightweight, NumPy-free driver for Pimoroni Display HAT Mini

displayhatmini-lite

A lightweight, NumPy-free Python driver for the Pimoroni Display HAT Mini — works out-of-the-box on Raspberry Pi Zero 2 W and other resource-constrained devices.

Why This Exists

The official displayhatmini-python library depends on NumPy, which:

• Has no prebuilt wheels for Python 3.13 on ARM
• Falls back to source compilation that takes hours on Pi Zero
• Often fails entirely due to memory constraints

This library provides a drop-in replacement using luma.lcd — a mature, lightweight display driver that works cleanly without NumPy.

Features

• ST7789 display (320×240) via luma.lcd
• RGB LED control with PWM brightness
• Backlight control (on/off or PWM dimming)
• Four buttons with callback support
• API-compatible with the original displayhatmini library
• Python 3.9+ including 3.13

Hardware

Function	GPIO (BCM)
SPI MOSI	10
SPI SCLK	11
SPI CE1 (CS)	7
DC	9
Backlight	13
LED Red	17
LED Green	27
LED Blue	22
Button A	5
Button B	6
Button X	16
Button Y	24

Please check official Pimoroni Display HAT Mini pinout for more information.

Installation

Prerequisites

Enable SPI on your Raspberry Pi:

sudo raspi-config nonint do_spi 0

Or add to /boot/firmware/config.txt:

dtparam=spi=on

Optional: Flicker-Free Backlight Dimming

For smooth, flicker-free backlight dimming, enable kernel PWM by adding this line to /boot/firmware/config.txt:

dtoverlay=pwm-2chan,pin2=13,func2=4

Then reboot. The library will automatically use kernel PWM when available, falling back to software PWM otherwise.

Hardware fix for completely flicker-free operation: Add a 0.1µF ceramic capacitor between GPIO 13 and GND. This eliminates all brightness spikes and dips, especially noticeable at mid-range brightness levels.

System Dependencies

sudo apt update
sudo apt install -y \
  python3-pil \
  python3-spidev \
  python3-rpi.gpio \
  fonts-dejavu-core \
  libfreetype6 \
  libjpeg62-turbo \
  zlib1g

Important: Install fonts and freetype before creating your virtual environment, otherwise TrueType fonts won't work in Pillow.

Install the Package

pip install displayhatmini-lite

Or for development:

git clone https://github.com/FireHawken/pimoroni-display-hat-mini-examples.git
cd pimoroni-display-hat-mini-examples
pip install -e .

Virtual Environment Notes

GPIO access requires system packages. Create your venv with:

python3 -m venv --system-site-packages .venv
source .venv/bin/activate

Quick Start

from displayhatmini_lite import DisplayHATMini
from PIL import Image, ImageDraw, ImageFont

# Create display instance
display = DisplayHATMini()

# Turn on backlight
display.set_backlight(1.0)

# Set RGB LED to purple
display.set_led(1.0, 0.0, 1.0)

# Draw something
image = Image.new("RGB", (320, 240), "black")
draw = ImageDraw.Draw(image)
draw.text((10, 100), "Hello World!", fill="white")

# Send to display
display.display(image)

# Button handling
def button_callback(pin):
    if not display.read_button(pin):  # Button released
        return
    if pin == DisplayHATMini.BUTTON_A:
        print("Button A pressed!")

display.on_button_pressed(button_callback)

API Reference

DisplayHATMini

Constants

# Buttons
DisplayHATMini.BUTTON_A  # GPIO 5
DisplayHATMini.BUTTON_B  # GPIO 6
DisplayHATMini.BUTTON_X  # GPIO 16
DisplayHATMini.BUTTON_Y  # GPIO 24

# Display dimensions
DisplayHATMini.WIDTH   # 320
DisplayHATMini.HEIGHT  # 240

Methods

Method	Description
__init__(backlight_pwm=False, spi_speed_hz=None)	Initialize display. Set backlight_pwm=True for dimmable backlight. Default SPI speed is 80 MHz.
set_led(r, g, b)	Set RGB LED color (0.0–1.0 per channel)
set_backlight(value)	Set backlight brightness (0.0–1.0)
display(image)	Send PIL Image to the display
on_button_pressed(callback)	Register button event callback
read_button(pin)	Read button state (True = pressed)
using_hardware_pwm	Property: True if using kernel PWM for backlight

Examples

See the examples/ directory:

• hello.py — Basic display and LED test
• pong.py — Classic Pong game using the buttons
• backlight_pwm.py — Backlight dimming demo

Technical Notes

Backlight PWM

When backlight_pwm=True, the library uses a 2 kHz PWM signal for smooth dimming:

• Kernel PWM (preferred): Uses /sys/class/pwm interface — rock-solid timing, no CPU jitter
• Software PWM (fallback): Uses RPi.GPIO.PWM — may have occasional brightness fluctuations

The library automatically detects and uses kernel PWM when the overlay is enabled.

Why 2 kHz? Higher frequencies (5–10 kHz) cause the backlight to appear black at low brightness levels (below 20%). At 2 kHz, all brightness levels work correctly from 0% to 100%.

Performance

The display runs at 80 MHz SPI by default, achieving ~17 FPS for full-screen updates. If you experience display artifacts, try lowering the speed:

display = DisplayHATMini(spi_speed_hz=52_000_000)  # 52 MHz

Migrating from displayhatmini

Replace:

from displayhatmini import DisplayHATMini

With:

from displayhatmini_lite import DisplayHATMini

The main API difference: this library doesn't use a numpy buffer. Instead, pass a PIL Image directly to display().

License

MIT License — see LICENSE for details.

Acknowledgments

• luma.lcd for the excellent display driver
• Pimoroni for the Display HAT Mini hardware