model RC as USB Joystick

Model aircraft pilots like to use PC-flight-simulator software to train the handling of model aircraft without the risk of the loss of real models. It makes sense to use the own model aircraft remote control (RC) as input devise for the software. This requires an adapter. This adapter has to convert the RC into a virtual USB-joystick. This adapter has to be connected to the teacher/student-connector
model RC as USB Joystick - schematic

of the RC, and acts as a USB-joystick with 5 axis and 16 buttons (only up to 14 buttons can be used). The joystick-controller is powered and controlled via USB. The capacitors C1 and C5 stabilize the supply voltage. C2 is stabilizing the USB-voltage if the internal 3. 3V-voltage regulator. The microcontroller expects the PPM-teacher/student-signal at the interconnected pins 12 & 13. These are Schmitt-trigger-inputs. The high-part of the PPM-signal has to be >4V and the low part has to be <1V. The polarity of the PPM-pulses (normal or inverted) is unimportant. The practical output voltage levels of teacher/student-signal vary from 0. 6V to 9V (depending on the brand). This signal has to be converted to the correct voltage level for the micro controller. The circuitry contains a level converter (R3, R2, C6, Q2) to convert nearly every signal level to the correct voltage level for the microcontroller. The adapter emulates a joystick with 16 buttons. If a 8-channel-RC is used, then only buttons 1. 6 are used. Every additional channel will use 2 additional buttons. A 12-channel-RC will use the buttons 1. 14. The other 2 buttons have no functions at the moment. I may use them for future functions or may remove them. Every channel controls 2 buttons. The first button becomes active, if the channels pulse width is below 25% (< 1. 25 ms). The second button becomes active, if the pulse with is above 75% (> 1. 75 ms).

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