Ted's Cessna Knobox

Part I (mechanical)

• a friction-locked throttle knob (I used A820)

• a vernier-style mixer knob (I used A790)

• hardboard, 3.5mm in thickness

• M3 screws x4 for securing the potentiometers to the holders

• M2 screws x4 for securing the knob ends to the potentiometer sliders

• (M2.5/M3 screws + nuts) x4 for securing the holders to the enclosure

• you'll need to laster-cut the hardboard and 3D-print the holders/sliders

Part II (circuitry)

• stmf103c8t6 board & ST-link programmer (something like https://www.ebay.com/itm/2pcs-STM32F103C8T6-ARM-STM32-Development-Board-Module-Blue-Pill-ST-Link-V2-USA/292168190439)

• slide potentiometer (10K, 88mm in length, https://www.amazon.com/gp/product/B07QVQ67MV/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1)

• 3 SPDT switches + 1 SPDT toggle switch

• 5 resistors (15K)

• micro-USB to USB type-A cable (https://www.ebay.com/itm/90-Degree-Left-Angled-Micro-USB-5pin-Male-to-USB-B-Female-Panel-Mount-Type-Cable/162358249642)

• (optional) mounting jig (https://www.amazon.com/gp/product/B07BHXXR4D/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 works very well, but you'll need to drill the holes yourself)

Holders: holder.stl

Sliders: slider1.stl, slider2.stl

Part 1: cessna-knobox-enclosure1.svg

Part 2: cesnna-knobox-enclosure2.svg

Configure the potentiometers as voltage diviers:

• Connect two ends to have 3.3v difference in voltage

• Connect the pivot pins to A1 and A2 of the microcontroller

Configure the switches as pull-up inputs:

• Connect the middle pin of all switches to the ground (G/GND)

• Parallel one side of the resistors (15K x5) to be 5V (5V pin)

• Connect the other side of each resistor as shown in the diagram:

  • One (left/right) pin from each of three switches connects to A8, A9, A10, respectively

  • Pins (left & right) of the fourth switch connect to B14, B15.

  • Note: the lower right switch is a SPDT switch that springs to off when no pressure is applied. It could be used as flap control.

(optional) To build the firmware from source, run ./build_image.sh (make sure you have Rust/Cargo installed on your computer)

Or you can use a pre-built image already available at ./cessna-knobox.bin

Flash the image to the microcontroller using ST-link (you can either use the tool provided officially by ST, or do it in openocd)