Saturday, July 15, 2017

Live Sectional Map

The Live Sectional Map is a small cylinder showing the aeronautical sectional chart around Sea-Tac. Seven airports are illuminated with colored LEDs. When the cylinder is plugged in, it will download the METARs for these airports every minute, and update the color for each airport depending on the conditions.

Just like ForeFlight, VFR is green, MVFR is blue, and IFR is red. LIFR flashes red.

The map was super glued around an old Quaker oats can. I wrapped it in rubber bands for a day to let the glue settle.

I drilled holes for each airport and hot-glued common cathode RGB LEDs to each airport.

After experimenting with an Arduino like I did with Thinking Man, I decided Arduinos are a pain to connect to WiFi, and Raspberry Pis are much more robust. I SSH'ed onto a RPi running Raspbian on headless mode while developing. The RPi's GPIO ports control each LED anode.

I used a simple GPIO breakout along with female-female jumpers to connect each LED. The cathodes were strung along this awkward extension, shown below. I used a 200 ohm resistor on ground for the whole circuit. Later I found out the red LEDs ate a lot more power, and would dim rival blue LEDs when in use. Rather than put 21 resistors on all of these anodes, I just balanced the color using pulsewidth modulation through the RPi.GPIO library. Code:

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