This project is for using a G25/27 shifter connected directly to your computer as a HID device without the need for the main G25/27 unit.
This is the pinout of the DSUB9 coming out of the shifter (female)
| PIN | Purpose | Wire Color |
|---|---|---|
| 1 | Clock | Purple |
| 2 | Serial Button Data | Gray |
| 3 | Shift Register Mode Parallel/Serial | Yellow |
| 4 | X Axis | Orange |
| 5 | Ground LEDs | White |
| 6 | Ground Logic | Black |
| 7 | +5V Short | Red |
| 8 | Y Axis | Green |
| 9 | +5V Short | Red |
The first step is to wire the shfiter I/O.
The inputs used by the project are defined in g27shifter.h. The button I/Os are assumed to all be on the same AVR port, these are defined by the BUTTON_PIN,** BUTTON_PORT** and BUTTON_IO.
Next up is defining which pin BUTTON_SHIFT_REGISTER_MODE_PIN, BUTTON_DATA_PIN, and BUTTON_CLOCK_PIN is on.
After that is connecting the X and Y pins to an ADC port each, these are defined by STICK_X_ADC and STICK_Y_ADC.
Next is powering the logic circuitry, connect pin 7 (or 9 for that matter since they're connected internally) to +5V or VCC and pin 6 to ground. I recommend not connecting pin 5 since that will power the leds and in turn reduce the voltage over the X and Y pots when powering from USB, doing this with an external power supply should work better.
Run the make file and flash the hex onto your AVR.
I've tested this with win-avr on a atmega32u4. avr-gcc and Atmels tool chain should work just as well.
You might need to adjust the ADC values for the X and Y axis used used for calculating the selected gear, these are also defined in g27shifter.h. Do this by wiring everything up then writing down the voltage on the X and Y pin for each gear in turn with everyting connected to USB.
For example: Voltage in first might be 1.3 for x.
Now we need to find the ADC value 1.3 and 3.7 corresponds to, since the ADC runs in 10bit mode using VCCREF so measure the voltage from VCC to ground, for example 5V.
The ADC value is then 1.3 / 5 * 1024. This should be the value for STICK_X_12.
Repeat for the other STICK_* values.
To make this compatible with a G25 shifter switch pin 1 and 7 going into the DSUB9, that is clock on pin 7 and +5V on pin 1.
Since the G27 doesn't have the sequential mode that is not implemented, but as seen in the schematic value 4 from the shift register tells wether the shifter is in H or sequential mode.
##Hardware operation The X and Y pins are simply potentiometers that tells how the stick is positioned. The buttons work through parallel in serial out shift registers. Pulling the mode pin low then holding it high latches the current input pins so that they can be sequentially read through the serial output. The shift register advances to the next value on the falling edge on the clock pin.
##Schematics
Showing that 1 and 9 are shorted in a G25
