Tuomas Vaherkoski

Programmer and electronics hobbyist

Throttle Quadrant

May 26, 2015

The Idea

I had had an idea of building this thing for a long time. It originally came from very annoying bug/feature of my wireless joystick which loses connection when left idle for some time. What happens then is that the throttle randomly jumps to full power making aircraft to do unwanted maneuvers… I also wanted to be able to control power settings of the plane more easily and realistically.

Throttle Quadrant

Building

This device is actually quite simple on hardware side. It takes power from USB (+5V) so you don’t need any battery. It’s build around AVR Attiny84 microcontroller.

Schematic

The microcontroller uses its internal analog-to-digital converter to measure voltage from center taps of slide potentiometers. There is also AVR-SPI connector for programming the chip and usb connection to speak with computer. Slide pots are color coded as (from left) throttle - prop pitch - mixture, but of course they can control anything you want.

There is still a few free pins (used only by AVR-SPI), so maybe I’ll add some switches and leds some day. It also definitely needs a better case with nice front panel.

Coding

I used VUSB library which implements slow-speed USB stack for AVR microctontrollers. Device is acting as USB HID joystick so the drivers are built in on every modern operating system (Windows XP or higher). Microcontroller runs in a loop which takes measures from ADC channels and then saves them so that computer can query the values.

It would be easy to convert this to any HID device, for example volume controller, you just need to change the usb descriptor.

Conclusion

The device is working great and it was cheap compared to ready-to-go kits so it definitely worth building. I’ve used this with Microsoft Flight Simulator X and IL-2.

If you are interested you can download schematics and source code, it’s open source. Schematic can be opened with KiCAD.