Use your Model-Aircraft-RC as Joystick

employing PIC18F2455

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General
Preface
Schematic
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General

Power supply:		via USB
Clock:		20-MHz-crystal
analog Axis:	5	8 bit resolution controled by Channel 1..5
Buttons:	14 max	controled by Channel 6..12
RC-Typ:		3... 12 Channel RC with PPM-Teacher/Student-output

Preface

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 most RCs have 8 channels. This adapter supports up to 12 channels. The minimum are 3 channels.

Schematic

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.

Q1, C3 and C4 feed the microcontroller with a stable 20-MHz clock.

R1 pulls up Pin 1 of the microcontroller to high level.

The circuit is designed for a PIC18F2455. However, PIC18F2458/2550/2553 can be used as well. (No changes at the hardware or HEX-file would be necessary.)

Teacher/Student-signal
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.
Never apply voltages above 5V or below 0V directly to the pins 12 &13 !

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 teacher/student-signal of the RC has to be connected to the connector JP1.

An LED can be connected to Pin 11 (RC0). This pin is high, if a valid teacher/student-signal is received.

Axis
The adapter emulates an 5-axis-joystick. The 5 axis are controlled by the Channels 1 ... 5 of the RC.

Buttons
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).
Chanel 6 ... 8 control the buttons 1 ... 6.
The Channels 9 ... 12 (if available) control the buttons 7 ... 14.

DIP-Switch S1
The DIP-switch S1 contains 8 contacts SW1..SW8. They can be used to modify the conversion of the PPM-teacher/student-signal into the joystick emulation.

SW8	SW7	SW6	SW5	SW4	SW3	SW2	SW1
invert Channel				unused	unused	Order of Channels

The first 4 axis of a joystick are in flight simulation programs by default used for the following functions:

Joystick Axis	1. Axis	2. Axis	3. Axis	4. Axis	5. Axis	6. Axis
Name	X	Y	Z	X-rotation	Y-rotation	Z-rotation
Function in PC	Aileron	Elevator	Throttle	Rudder	-	-

This is identical to the function of the first 4 channels of a Futabe-RC. But RCs of other brands use a different order. The adapter can change the order of the channels. This reordering is controlled by the positions of the contacts SW1 and SW2.

SW2	SW1	RC-Typ (Brand)	Channel 1	Channel 2	Channel 3	Channel 4
open	open	Futaba / Hitec	Aileron	Elevator	Throttle	Rudder
open	closed	Graupner / JR	Throttle	Aileron	Elevator	Rudder
closed	open	MPX / robbe	Aileron	Elevator	Rudder	Throttle
closed	closed	Sanwa	Elevator	Aileron	Throttle	Rudder

RC-channel 5 is always assigned to joystick-axis 5. It is normally used as second (right side) aileron-channel. Flight simulations don't need this.

The contacts SW5 ... SW8 can be used to invert the channels 1 ... 4. If a contact is closed then the related Channel will be inverted. This feature is not very important, because the very most RCs can invert the signals too.

SW8	SW7	SW6	SW5
Channel 4	Channel 3	Channel 2	Channel 1

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History

08.06.2012
Bugfix: moved 2nd input from pin 24 to pin 12 (for use without bootloader))

07.06.2012
Update
- number of buttons reduced to 16
- voltage level at pin RC0 indicates a valid teacher/student-signal

06.06.2012
Update

05/06.06.2012
Prototype

back to other projects , PIC-microcontrollers , Electronic , Homepage Author: sprut
created: 06.06.2012
last change: 08.06.2012