Hello,
I have just finished a new USB interface project (2:45am here in Brazil).
When Walter Zanette published his project of an USB RC interface, I got inspired to design my own.
My project reads up to 8 channels and appears to Windows as an 8 axis joystick (X, Y, Throttle, Rudder, Dial, Slider, Aileron and Elevator).
I tested it with a Futaba SkySport FP-T6VA (6 channels). Windows 98SE recognized only 5 channels, but Windows XP Home recognized all 6 channels.
The interface works equally well with both signal polarities.
Of course a project that is just like all the others already available is not big deal, so I added some new stuff:
- The PPM signal timing is done in hardware (CCP module of PIC microcontroller). This leads to high resolution/high stability readings. The resolution I obtained was 8192 steps for full stick throw (0.82ms to 2.18ms PPM pulse width), but I divided it by 32, so each channel fits in a byte. If the extra resolution is required, the firmware may be changed. The signal is rock steady, no one can see the slightest jitter in the bars, with the sticks not moving of course
- I added a DC-DC boost converter, to convert the 5V from USB to 9.6V, so the transmitter (the Futaba ones at least) is powered by the interface, via the trainer connector. This way, the RF power section doesn't get powered, just the coding section, so no RF is radiated. The power switch of the TX remains off all the time, the battery is not drained and there is no need to remove the crystal of RF module. This is the best part, I think.
- The project will be published for free, complete with all schematics, source code (under GNU GPL, perhaps), PCB layout, etc.
This way, I hope, several people can enhance my project, to fit other needs.
Some improvements I already envised:
- Multiple USB reports, so the 8 byte report limitation can be broken. This way more channels, with more resolution may be used.
- Channel reordering (nice idea Walter), so the correct functions can be assigned to different TXs brands.
- Add a joystick port to the interface, so it becomes dual-mode: RC to USB converter and also joystick to USB converter. Perhaps two people may use it simultaneously.
The microcontroller is plenty of free pins, so there is room to many ideas...
When I get everything documented and debugged, I will publish it. The only problem is that I don't have a home page to upload it, so I expect someone offers to host the files.
Best regards,
Isaac