model RC as USB Joystick

Model aircraft pilots utilize PC flight simulator software to practice handling model aircraft without risking damage to real models. It is advantageous to use the actual model aircraft remote control (RC) as the input device for the software, necessitating an adapter. This adapter converts the RC into a virtual USB joystick and connects to the teacher/student connector of the RC, functioning as a USB joystick with five axes and 16 buttons (though only up to 14 buttons can be utilized). The joystick controller is powered and managed via USB. Capacitors C1 and C5 stabilize the supply voltage, while C2 stabilizes the USB voltage from the internal 3.3V voltage regulator. The microcontroller receives the PPM teacher/student signal at interconnected pins 12 and 13, which are Schmitt-trigger inputs. The high part of the PPM signal must exceed 4V, and the low part must be below 1V. The polarity of the PPM pulses (normal or inverted) is not critical. The practical output voltage levels of the teacher/student signal range from 0.6V to 9V, depending on the brand. This signal must be converted to the appropriate voltage level for the microcontroller. The circuitry includes a level converter (R3, R2, C6, Q2) to adjust nearly any signal level to the correct voltage for the microcontroller. The adapter emulates a joystick with 16 buttons. If an 8-channel RC is used, only buttons 1 to 6 are activated. Each additional channel will utilize two more buttons, meaning a 12-channel RC will use buttons 1 to 14. The remaining two buttons are currently non-functional but may be repurposed or removed in the future. Each channel controls two buttons, with the first button activating when the channel's pulse width is below 25% (< 1.25 ms) and the second button activating when the pulse width exceeds 75% (> 1.75 ms).

The adapter circuit design incorporates several key components to facilitate the conversion of a traditional RC signal into a format compatible with USB joystick protocols. The primary function of the adapter is to interpret the PPM (Pulse Position Modulation) signals generated by the RC transmitter and translate these signals into joystick movements and button presses that can be recognized by the flight simulator software.

The microcontroller serves as the core processing unit, interpreting the PPM signal received at its Schmitt-trigger inputs. Schmitt triggers are utilized to ensure clean transitions between high and low states, which is critical for accurate signal processing. The input voltage levels are conditioned using a level converter circuit comprising resistors (R2, R3), a capacitor (C6), and a transistor (Q2). This configuration allows the adapter to accommodate a wide range of input signal levels, ensuring compatibility with various RC transmitters.

Power for the circuit is supplied via USB, with capacitors C1 and C5 playing a crucial role in stabilizing the voltage supply, preventing fluctuations that could affect the operation of the microcontroller and other components. Capacitor C2 specifically stabilizes the 3.3V output from the internal voltage regulator, which is essential for the microcontroller's operation.

The joystick emulation aspect of the adapter is achieved through the mapping of RC channels to joystick buttons. Each channel from the RC transmitter is monitored for pulse width variations, which dictate the activation of corresponding buttons. The logic for button activation is based on predefined pulse width thresholds: a pulse width below 25% activates the first button, while a pulse width above 75% activates the second button. This setup allows for intuitive control in the flight simulator, providing pilots with realistic handling experiences.

Overall, the design of this adapter not only enhances the training experience for model aircraft pilots but also demonstrates the versatility of RC technology in interfacing with modern computer systems. The potential for future expansions, such as the addition of more buttons or functions, indicates that this adapter can evolve alongside advancements in flight simulation software and RC technology.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 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). 🔗 External reference