This micro altimeter is based on the original MAV ALTIMETER with BMP280 barometric sensor – it is virtually the same, except the pressure sensor which was replaced by MPL3115A2 and the hardware ID was removed, leaving only the software ID. This altimeter is extremely light – about 0.35gr and with the battery it weighs less than 1 gram. This device is missing the hardware ID number and therefore it is only partially compatible with the requirements of the FAI association. Please note that this is not a commercial product but free to use and copy for non-profit use under the GNU General Public License.
The main characteristics of this altimeter are:
- Size: 8mm x 8mm
- Weight: 0.37gr without battery, 0.87gr with battery
- Power supply: 2.6v to 4.2v and 1.5mA average consumption
- Built-in hardware and software serial number
- Unique digital 1min time-altitude signature
- Sampling speed is either 20 or 40 samples per second
- Total record time 800 or 400 seconds
- Adjustable start-preparation time between 1 and 60 minutes
- Protection from reversed battery polarity
- Capable of working with a single CR927 – 3v battery
The MAV altimeter uses the inexpensive MPL3115A2 sensor which is controlled by the Microchip’s PIC12LF1840 microcontroller and information is recorded in a 512Kb I2C EEPROM memory bank. BTN as indicated in the schematic is not an actual button but two bare pads on the PCB which have to be brought in contact. D2 is there to protect the device from reversed polarity when the battery is connected. Considering the low maximum voltage requirements of the PIC12LF1840 and the MPL3115A2, this diode should have a Vf (forward voltage) of at least 0.6v in order to prevent overvoltage when using a fully charged Li-Po battery up to 4.2v.
The MAV altimeter is set-up and the information can be downloaded through the USB reader where the MAV altimeter is plugged to. This USB reader has a built in 3.3v power supply for the MAV altimeter.
I made the software for this altimeter of two different applications. The USER application is the main application which is normally used. This application allows you to format the memory (not the Digital time-altitude signature), download and visualize the recorded data. You can also setup the recording speed between 40 and 20 samples per second, and the pre-flight setup time, however you cannot change the software ID number.
The SERVICE application is for device maintenance purposes only. Beside the normal USER settings, it allows you to change the software ID number and to adjust the sampling clock. Because the MAV altimeter is using the PIC18F1240 internal clock which is normally accurate within 1%, in some cases it might need adjustment if the accuracy is worsen for whatever reason.
And finally the flow chart for the MICRO ALTIMETER’s internal logic organization and LED indications.
TECHNICAL AND USER FILES:
BOM_MAV
BOM_MAV_USB
Firmware – HEX
PCB – CADCAM
USER AND SERVICE APPLICATION
How long is the battery life. Is that a rechargeable lithium cell and how is it charged?
The battery is a coin 3v lithium battery, these are not rechargeable. But a CR927 battery lasts about 1h – 1h30min, this is probably about 10 flights. Given the low prices in E-bay (5 for one dollar), it is not worth trying to recharge them.