Month: June 2019

A battery management system needed to be added and this proved to be tricky. For convenience we want a rechargeable battery and, like any gadget, to be able to charge it from USB. The unit draws 170mA and I opted for a 1000 mAh lithium battery which includes battery protection from overcharge, short-circuit etc. This should see up to 5 or more hours use. I used a charge management chip and programmed the charge current to 300mA. This conservative charge rate means a very safe 3.5hr charge time and doesn’t demand too much from the battery.

Prototyping The Case

I wanted to make a device that was as small and lightweight as possible. After modelling the display PCB, all the other parts were modelled as accurately as possible. Finally we know the minimum size the case can be. Originally I designed it with screws, but then I realised I was still thinking like it would be made from milled metal – now I can 3D print a case I can make it snap together. Note the two tabs on the top part which snap in to the bottom part. The thinnest shell I was comfortable with was 2mm and this makes the case a feather weight and yet still surprisingly rigid.

For the switch I tried a few different things and again I was thinking along the wrong lines. Plastic allows you to make flexible parts. The switch can be made out of the body in one piece, which is quick cheap and simple. Just cut a slot so it can move. I added a raised area to make it easy to find and since the print direction is left to right, its optimal for the 3D print. It worked really well and I’ll definitely use this technique in future. I wanted a black case, but have lots of white PLA that I needed to use up so the prototype cases were white.

The software was updated to hook up the ADC input to monitor battery voltage. A housekeeping task runs once per second and this monitors the voltage and displays approx capacity rounded to the nearest 25% – for simplicity.

Next Steps

• Go flying with it!
• Battery percentage calibration
• Printed Circuit Board design and manufacture

In the previous project, we saw a traffic display involved a far bit of hacking of the Pilotware unit. The downside of this is that it makes it difficult to keep the Pilotaware unit up to date.

The Pilotaware unit provides traffic information via a Wifi hotspot. The system provides an interface on port 2000 which provides FLARM and NMEA GPS information.

What we need is something lightweight, cheap with wifi and a display. Until recently this would have been an expensive development, but today we have the internet of things. Esspressif systems have made this extremely easy with a system of a chip, which includes WiFi, can easily be programmed in C++ using arduino compatible libraries …..and all for the price of a McDonalds! It should be possible to create a unit about the size a fag packet that you can stick the dashboard for very low cost.

All that is required is to connect the esp8266 serial peripheral interface to the display. In this case I used a wimo d1 mini board.

Next we need to connect to the PAW which is only a couple of lines of code, then connect to port 2000 and handle the data stream. Once that’s done we install some SPI display libraries and we can draw whatever we want on the screen.

I chose to depart from the TCAS display symbols because I’m not used to them and I found a ‘spaceship’ pointing towards me far easier to interpret than squares moving sideways. Other than that the large number indicates the level and I can display the reg or whatever with it.

Next Steps

• 3D printed case
• USB Rechargeable lithium battery – gives about 7 hours of use from a 1 hour charge.
• Battery level monitor
• If it can’t connect to PAW show a demo
• A funky start up screen
• Single button power on and off