Air Data Instrument

Under construction

Written by Ian Johnston
Posted July 24, 2011
Updated February 1, 2012

The Dangerpants Labs Air Data Instrument (ADI) is a simple, Arduino-based instrument which reads ambient air pressure, ambient air temperature, and differential air pressure, as well as incorporating a real-time clock.

Through these readings, it calculates airspeed, altitude, and vertical speed. It displays these values, along with temperature, and time in 24 hour format on a 16x2 character LCD.

The Dangerpants Labs ADI was inspired by a desire to have flight instruments on a motorcycle, without having the panel space required by actual steam gauges.

IMPORTANT DISCLAIMER

The Dangerpants Labs ADI is NOT FOR USE ON AIRCRAFT. See the full disclaimer for more information.

Prerequisites

In order to be successful with the Air Data Instrument, you need to have some skills already under your belt. These documents assume you already know how to:

  • Solder
  • Read a schematic
  • Operate technical software
  • Think

Specifically, you will be soldering either breakout boards or individual components in a printed circuit board (including surface-mount). You will need to read the schematic diagram to troubleshoot problems and ensure connections are sensible. Loading the firmware onto the Arduino or Atmega328P processor requires use of the Arduino IDE.

Parts

The ADI can be built using the following parts:

  • Arduino Uno (or equivalent with ATmega328 processor or better)
  • Bosch BMP085 - available from Spark Fun
  • Freescale MPXV5004DP (or similar from Freescale) - available from DIYDrones
  • Maxim DS1307 - availble from Spark Fun, Futurlec and a variety of other suppliers
  • Backlit 16x2 character LCD - various suppliers
  • A few momentary switches and small parts
  • Some variety of project enclosure

A single-board PCB is currently in development. Once it's finished, plans will be posted here (see below under Documentation for initial, unfinished documents). The PCB version will require surface-mount soldering techniques, which will be documented in the Construction Guide.

Additional parts

In addition to the ADI itself, you will need a ram-air source and a static air source. The prototype uses air pressure inside the project box (in a land-based application -- this would not be appropriate for air-based installations where altitude data is more critical and variable). Ram air is provided by a pitot tube made of aluminum tube oriented roughly into the oncoming air stream, connected to the differential pressure unit by silicone tubing.

For more information on constructing a good pitot-static system, refer to EAA publications and various aircraft homebuilder books and websites on the subject.

Construction

Insert wiring diagram here

Circuit construction is straightforward. The MDXV5004DP differential pressure unit outputs an analog voltage, and is read by one of the Arduino's analog I/O pins. The BMP085 ambient pressure sensor and DS1307 clock module communicate via I2C in the standard setup used in Arduino projects. The LCD is connected via a number of the Arduino's digital I/O pins.

Try to keep wire runs short and parallel when possible. For the prototype, the various break-out boards are simply wired together on a proto-shield. The custom PCB will reduce costs and make a physically smaller project, but SMT soldering requires more equipment and skill than soldering together break-out boards.

The prototype is not yet properly enclosed, but it will eventually be housed behind a custom faceplate in a basic aluminum box for mounting to a motorcycle. The CAD file for the faceplate will be available here once it's been created.

The Freescale MPXV5004DP breakout board is no longer available from DIYDrones. Any similar part should work as well, as long as it measures 1.5 kPa or more positive pressure. The ADI uses an AREF voltage of about 2.5V, giving 1.5 kPa as the maximum reading. 1.5 kPa works out to about 110 MPH, which is plenty for ground operations. At 4.5 kPa max, the 5004 is capable of sensing up to 185 MPH.

(A full Construction Guide is coming soon.)

Software

The software is written with the Arduino IDE (v0022), and takes about 21k of program space in its current incarnation. Around 10 EEPROM bytes are written for preferences. The source files are split out roughly by function.

The current version of the software is adi-software-v0.9.1.tar.gz.

Video

I've recorded a number of videos as I've made progress with the project:

Documentation

Current documentation includes this page, and the following documents:

License

The Dangerpants Labs Air Data Instrument is presented under the Creative Commons BY-NC-SA 3.0 license. This means you are welcome to use it for anything you like, including making derivative works, as long as you credit me, retain the same sharing agreement, and don't use it for commercial purposes.

Practically, this means I want this project to remain free for everyone. Use it, make it better, whatever. If you want to sell it, you must contact me to arrange for different terms.

Copyright © 2011 under CC BY-NC-AD 3.0 terms. Created by Ian Johnston. Questions? Please mail me at reaper at obairlann dot net.

Latest News

January 13, 2012 - It works!

It works!

The v1.0 board isn't perfect, but the problems are easy to fix. Progress!

January 12, 2012 - Soldered up!; Missed connection

I created a solder stencil and soldered up the board. No smoke test yet, but it sure looks pretty.

I also discovered my first definite mistake on the board -- LCD connector pin 12 is +5v, but should be ground. No biggie, and easily worked around, but will be corrected in the next version.

January 4, 2012 - Parts all fit; 71g

Out of curiosity, I stuffed the board to see if everything fit, and huzzah, it does! I also weighed all the pieces: the ADI, minus case, weighs a mere 71 grams.

January 3, 2012 - PCB arrived, times two!

My board arrived from BatchPCB today, and I was thrilled to discover two boards instead of one. I get a free do-over board, hooray!

December 27, 2011 - PCB shipped; Schmancy new logo

BatchPCB reports that my PCB has shipped, and I should have it in my hands by the end of this week, or early next week. Hooray!

I've refreshed the ancient Dangerpants logo to look a bit nicer, and added a Dangerpants Labs logo to this page.

December 19, 2011 - Shopping list!

Updated the Bill of Materials with a shopping list at Mouser. Almost everything you need to buy except the BMP085 barometric pressure sensor, PCB and buttons to build the basic ADI. All told, looks like parts will run under $50 for one ADI. Note: do not buy anything yet! This is not yet a proven design.

December 8, 2011 - PCB Submitted

The v1.0 PCB design is off to the fab house. I expect it back in early January, and I should be able to build up my first single-board ADI by early February. Expecting to have to re-design, though.