Digital Avionics Prototype

Basic Aviation Instrument for a Microlight Trike

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This project documents the first prototype (around 2015) of digital avionics for my microlight. Due to inflexible design, scope creep and program memory limitations, it was scrapped in favor for the ModAir project


  • Ground Speed
  • True Heading
  • True Altitude
  • Altitude at standard pressure (Flight Level)
  • Date and Time
  • Flight Time
  • Pilot Checklist / Notes
  • Battery Voltage
  • Outside Air Temperature
  • Headlight Control
  • Heat-pad Temperature Control
  • Engine RPM Meter
  • Fuel Level
  • Water Temperature
  • USB Charging Port


The schematic consists of a PIC microchip, GPS module, some MEMS sensors and a Rotary Encoder:

I used a NT-G128641A Graphic LCD module (KS0108 controllers). Transflective STN-type graphic or character LCD modules are the most easily readable in an open cockpit. Color TFT Screens are almost impossible to read with the glare, and require sun-shielding.

GPS is a Ublox NEO-6M module, programmed (via USB serial cable and their software tool) to output binary POSECEF, POSLLH, STATUS, TIMEUTC, and VELNED packets at a rate of 10 Hz.

The PWM outputs were used for the headlight, and for heat-vest temperature control. The Rotary Encoder user interface worked very well, even in winter with thick gloves. Using the touchscreen on a phone or tablet is almost impossible while flying.

This first prototype was hacked together on veroboard with parts I had lying around. With all the menus and functionality, the 24 KB program memory on the PIC18F4455 was quickly running out.

Many sections in the firmware have been commented out to save program memory. Besides the program memory limitations, this design lacks in modularity. I needed to remove the electronics from the aircraft at the airfield, and take them home every time I wanted to add functionality (which happened a lot...).

Qt Creator project, simulating the LCD graphical drawing routines and menu look-and-feel

Zip Archive - 11.39 kB - 04/15/2017 at 06:44


Original prototype firmware (C code for XC8 / MPLAB X) and schematics (Cadsoft Eagle + JPG)

Zip Archive - 165.56 kB - 04/15/2017 at 05:53


  • 1 × NT-G128641A Graphic LCD module
  • 1 × PIC18F4455 Microprocessors, Microcontrollers, DSPs / Microcontrollers (MCUs)
  • 1 × Ublox NEO-6M GPS Module
  • 1 × BMP085 Module Sensors / Barometers

  • Qt Graphic LCD Simulation

    Rene04/15/2017 at 06:50 0 comments

    I wrote a small Qt application to simulate what the different menu's would look, as it was simpler to debug / develop on the PC rather than reprogramming the PIC the whole time...

    The above screenshot shows the typical home screen before the RPM sensor was added.

View project log

  • 1
    Step 1

    This project was uploaded as a reference only, and the ModAir project aims to address all it's shortcomings...

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