ModAir - Modular Aviation Instruments

Open Source Avionics for Microlights and other Non-Type-Certified Aircraft

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With electromechanical avionics becoming obsolete and expensive to repair, many analog gauge-type instrument panels are being replaced with an electronic flight instrument system (EFIS). Sensors and displays are cheap and readily available, yet commercial EFIS systems remain ludicrously expensive.

This project aims to create a low-cost EFIS system for non-type-certified aircraft such as:
- Ultralights
- Microlights
- Experimental aircraft
- Light sport aircraft

To support the various engine types, cockpit layouts, display sizes, sensors and required functionality, the system is built around a multi-master bus architecture. Measurements are periodically broadcast on the bus by sensor modules, while other modules monitor, control, display, log or forward this data.

Project Goals

The main goal of this project is to supply an open source infrastructure for avionics development. Each aircraft has different budgets and requirements for aviation instruments; trying to address them all with a single module is unrealistic. A modular approach splits functionality into reusable components. This makes it easier to maintain, replace faulty units, and upgrade by adding modules instead of replacing the entire system. An example is shown below:

Another advantage of the modular approach is that the

project can be completed in stages, with nice-to-have features being added

later. As a pilot, having access to real-time, reliable and relevant information

greatly assists in the decision making process. Adding additional instruments

thus becomes another way of making aviation safer for everyone sharing the

airspace. With the centralised design of the original prototype, I needed to

remove the electronics from the aircraft every time I wanted to add

functionality. This resulted in not being able to fly while features were

developed (which usually took longer than expected), or consequently not

developing features because I wanted to fly.

The end goal is to have a library of modules that can be mixed and matched to suit different pilot and aircraft requirements. Examples of modules include:

Module Features Status
Rotax 582 Engine RPM, EGTs, H2O, fuel level, fuel flow, relay and open drain outputs


5.8" Graphic LCD
ERM25664 256x64 monochrome (White on Blue)


3.0" Graphic LCD
Nelytech NT-G128641A 128x64 monochrome (Black on White)


3.0" Graphic LCD Generic QC12864B 128x64 monochrome (White on Blue)


2.5" Character LCD
Generic 1602A 2x16 character monochrome (White on Blue)


Navigation Waypoints, GPS, IMU, altitude, air speed


Computer Interface Allows PCs, tablets, smart phones and smart watches to be used as multi-functional displays (MFD)


Single board computer (RasPi / BB) with HDMI LCD screen


2.2" Graphic LCD Nokia5110 84x48 monochrome idea
2.2" TFT LCD Generic ILI9341 240x320 SPI serial color idea
Aircraft Interfaces
Outputs for fuel pump, lights, flaps, trims, heater, gear, ...
VHF Transceiver Interface Remote interface for airband radio
Transponder Interface Remote interface for ATC transponders, altitude encoder for older Mode C types idea
Aircraft Intercom Annunciation, volumes, PAX idea
Situational Awareness SDR-based ADS-B receiver, air-band channel activity indicator idea
Air-to-air Communication Low-cost ISM-band position broadcasting (similar to ADS-B in and out) to keep track of other aircraft in your squadron idea
Black Box Logging to micro SD card idea
Power Alternator and battery management, voltage and current idea

Personal Goals and Current Priorities

My main goal is to develop an advanced avionics system for my weight shift controlled (WSC) microlight trike (see background post). Being an open cockpit, my requirements might not always align with other pilots expectations. For example, touchscreen interfaces are almost impossible to use in-air (e.g. typing, zooming, panning); especially when fighting bumpy air and with thick gloves. Physical buttons, knobs and rotary encoders work quite well though. Depending on the angle of the sun, most TFT LCDs are challenging to read. Transflective STN LCD panels on the other hand, are easily readable in direct sunlight.

My current priorities are as follows:

  1. Fix up the firmware for the LCD modules and Rotax 582 Engine Module. The main focus is on making the various settings available through the menu's rather than the current hard-coded hack.
  2. Design the Navigation module PCB so that I can send it off for manufacturing (June 2017)
  3. Focus on the Computer Interface module and start looking at some 3D frameworks for moving map and synthetic vision [Android or Linux] (July 2017)

System Design

Requirements drive design. Read that again but slower. This project has three simple requirements:

  • Open source: design files and source code (for hardware, firmware and software) are hosted on GitHub under the GPLv3 license. This means that the contributions to this project may not be used in any closed source projects. Anyone is free to use the code for private and/or commercial use, but needs to publish any modifications under the same open source license.
  • Physically modular: modules (consisting of sensors, control outputs, interfaces, and/or displays) plug into a shared bus. Each module provides a specific set of features (also see overall feature wishlist) based on its attached peripherals. A module should be less than $100; if a set of peripherals exceeds this, the functionality should be split into smaller modules.
  • Modularity in terms of software: no firmware updates should be needed if a new module is added onto the bus. All the functionality related to the new module (which might be unknown at this point in time) needs to be self-contained. Having access to all other sensor readings on each module allows for some interesting data fusion and new parameters. For example, the module that measures the fuel level can also calculate the fuel endurance and range with the current tank, based on the ground speed and average fuel consumption.

On the display modules, this modularity is achieved by allowing the user to add widgets onto the screen, and linking them with sensor parameters as shown in the diagram below.

This approach applies to all display modules; whether small 2x16 character LCDs, monochrome graphical displays, Smart-phones, tablets or large colour TFT LCD screens. Widgets can be simple text, graphical items like gauges and bars, graphs that plot parameters (over time or against other parameters), attitude reference lines, 2D moving maps, or full 3D components such as synthetic vision (using topological maps and taking position and attitude sensor inputs).

For sensor modules, modularity is realized with a remote menu that can be accessed by a display module. This remote console can be used for configuration, alarm setup, viewing status, editing the value broadcast rate and any other options relating to the sensor.

This also greatly simplifies the communication protocol. There is no need to define message types for calibration or any other sensor-specific data. Similarly, the display modules and rest of the system need no prior knowledge of how to handle custom user data. User inputs can be simple up/down/ok/... buttons, rotary encoder inputs, or any characters from a keyboard.

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  • Lesson Learnt: Shielding

    Rene05/23/2017 at 19:42 0 comments

    Last weekend I got the firmware to a state where it could be used in the aircraft and installed it all into the pod... Not very pretty, but it'll do for now.

    During my pre-flight checks I noticed that the radio was picking up interference (the SQL had to be set all the way up to suppress it); Upon closer inspection with the oscilloscope I noticed that the switched mode power supplies were ringing around 100 MHz during both the rising and falling edges... Additionally the Microchip PIC is set to run at 119.763 MHz. The capture below was taken with a floating probe around 5-10cm away from the SMPS.

    Re-wiring the electronics with shielded cables (and connecting only ONE side of the shield to ground) fixed the issue. It's clear that each of the modules as well as all interface cables should be properly shielded to suppress their emissions, and shield them from the VHF radio and transponder RF!

  • Other CAN-bus Aviation Protocols

    Rene04/22/2017 at 12:29 0 comments

    This section tracks and compares various aviation-specific CAN-bus protocols. Being open source, support for these protocol can always be added at a later stage if required.

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  • Other Open Source Avionics

    Rene04/22/2017 at 11:56 0 comments

    This section tracks other open source avionics projects, for the purpose of collaboration and design reuse. Please let me know if you know of any other initiatives.

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  • System Bus Decision

    Rene04/22/2017 at 10:21 0 comments

    The entire design is built around a shared bus, into which multiple modules, interfaces and screens are plugged in. With various sensors asynchronously producing data, a one-to-many bus that supports message broadcasting is required. This leaves us with some options...

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  • Feature Wishlist

    Rene04/20/2017 at 12:53 0 comments

    I find it useful to envision as many future requirements as I can think of. That way the architecture can be designed with future upgrades in mind, even if these features are never actually implemented.

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  • Background

    Rene04/20/2017 at 12:49 0 comments

    I have always dreamed of flying and was fortunate enough to be able to complete my recreational pilot license a few years ago. South Africa is an amazing country to explore by air, especially in an open cockpit of a Weight Shift Controlled (WSC) trike!

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  • First Batch: Assembled Modules

    Rene02/05/2017 at 13:21 0 comments

    For the first manufacturing batch, I decided to focus on the bare essentials: LCD screen module and engine monitoring module. The screen module PCB was designed to fit some of the more common graphic and character LCDs from China. Here are some pictures after soldering and assembly.

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radiusmike wrote 04/07/2017 at 03:57 point

Great project.  I am a pilot and have owned aircraft, so am very familiar with this technology and think your approach makes good sense, I am building a set of instruments for my Honda Pilot ATV starting with EGT and CHT.  Am willing to help out here and there when/where I can.  

  Are you sure? yes | no

Rene wrote 04/07/2017 at 07:20 point

Thanks! If your EGT/CHT thermocouples are type-K, I found the MAX6675 very useful. Schematics and firmware are on Github. Good luck with your ATV and thanks for your offer to help

  Are you sure? yes | no

yesnoio wrote 04/05/2017 at 22:39 point

Hello Rene! An excellent project indeed! I would like to help with your project. I have little time, these days, but I did start an open-spec project a few years ago to help solve many module-related obstacles we face. It is largely built around aviation/industrial connectors. It has the protocols (CAN, I2C, SPI)  & topology you require. The project is listed on my profile. I'm eager to learn more about your project and help in any way I can (perhaps, even, with some long-distance prototype collaboration). All the best...

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Rene wrote 04/06/2017 at 19:58 point

I quite like your open-spec project... Will spend some time reading :) Thanks for your support and offer to help

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wintercabin2007 wrote 04/05/2017 at 22:20 point

I have a Lancair 360 that I can use to test any of your systems.  There are existing CHT, EGT and Fuel flow sensors and I have a variety of parts (Raspberry etc) that could be incorporated.  I did do some experimenting with National Instruments stuff (accelerometers etc) but things have changed substantially over the past 4-5 years. I also found trying to source sunlight readable displays a problem , hopefully you have had better luck.   Let me know if there is anything I can do to help including a financial contribution.  

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Rene wrote 04/06/2017 at 19:55 point

Thank you for your willingness to help. I really appreciate it; will keep you updated!

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samern wrote 04/02/2017 at 11:51 point

Absolutely.  I am a bit far from first flight in my Corvair Cruiser or Zentih, but I can code and I certainly can build and most defintely test.

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samern wrote 03/31/2017 at 21:57 point

As a pilot and Experimental Aircraft builder I would love to help in any way I can.  I am willing to also build variants and take them up when I fly and report on how well they work or respond.  I love the idea of modular instruments given the crazy cost and maintenance grief of MFDs, PFDs and EFIS systems these days.  You just know Synthetic Vision is going to have to be part of this, right?  Touchscreen and RasPi goodness!

  Are you sure? yes | no

Rene wrote 04/02/2017 at 11:42 point

Excellent! Thank you for your offer to help and feedback... YES!!! Just thinking about all the options with Synthetic Vision is exciting: terrain, airspaces, approaches, obstacle avoidance, etc... For the next few months the focus for me will be more on the sensors, hardware and firmware, but I'm really looking forward to the software side of things too :) You are more than welcome to get started on that so long. I would also appreciate any design inputs and suggestions. Thanks again for your willingness to help

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