Backup Air Data And Sensor Platform
BADASP isn’t a product name it’s just easier to say than “microcontroller based sensor platform”. I had to come up with something. The logo would be awesome though 🙂
This sensor platform integrates easily available inexpensive sensors into a small enough package to mount under your wing as a backup source of data for airspeed, magnetic heading, orientation, altitude and vertical speed. It relies on using the Stratux ADS-B receiver as a WiFi access point. It broadcasts its data on the Stratux broadcast address which is expected to be received by the Stratofier app.
The Circuit Diagram
The ugly prototype
Wemos D1 Mini 8266 Microcontroller with built-in WiFi and battery charge circuit. Note that these are available under a lot of different names and slightly different configurations. The one pictured here has a battery socket pre-mounted and pre-soldered to the board. The final build could be slimmer by placing the battery in front or behind the other sensors. The battery clip is extremely stiff so I’m not worried about it falling out.
Adafruit BNO055 9 DOF orientation sensor. This sensor also has a magnetometer but it is not accurate enough (see magnetometer listed below). BADASP only uses the orientation and acceleration axes.
Adafruit BMP388 air pressure sensor. This provides outside air pressure necessary to calculate correct pressure altitude. After limited testing, the accuracy has been within about 2 or 3 feet.
PNI RM3100 Magnetometer sensor. The sensor I used has an SPI interface instead of I2C like the others but it is very small. They offer an I2C version but it looks to be a fair bit larger. You’ll need to make modifications to the software if you plan to use the I2C version.
3D Robotics 4525DO pitot-static sensor. This was the most accurate with the highest rated airspeed I could find and it is also digital. Many of the ones available for models are analog. There is no getting around the fact that you’ll need to calibrate this for each individual aircraft. Stratofier has an entry in the settings for calibrating the speed for your aircraft.
The currently working software is available on GitHub here.
The Data Stream Format
The data sent from BADASP is a simple UDP stream sent to 192.168.10.255, port 45678. Stratux is only acting as a WiFi access point. The data is actually combined in the Stratofier app. The Stratux software could be modified to use the data directly but that wasn’t the goal of this specific project. The data is sent as (without any carriage returns or line feeds):
<Magetic X Axis>,
<Magetic Y Axis>,
<Magetic Z Axis>,
<Orientation X Axis>,
<Orientation Y Axis>,
<Orientation Z Axis>,
<Acceleration X Axis>,
<Acceleration Y Axis>,
<Acceleration Z Axis>
This page is in the process of being updated as time allows. The small bit of information here should be enough for you to build one if you’re familiar with microcontrollers and the hobby type sensors used in the project.
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