Demo

Circuit

This is the schematics for a PIC USB gamepad that I have built in a steering wheel shell. The code for the firmware was written in PicBasic Pro and it implements a HID USB device with 2 axes and 4 buttons (only 2 buttons connected in the prototype). The device is detected by Windows XP/Vista as a standard USB gamepad and can be used with many games and applications.

I am using a 2 Axes Buffered ±2g Accelerometer from DIMENSION ENGINEERING, it has a built in voltage regulator that allows powering the accelerometer dirrectly from the USB bus (5V):

http://www.dimensionengineering.com/DE-ACCM2G.htm

I highly recommend this accelerometer as well as other great Dimension Engineering products, check out their website: www.dimensionengineering.com !

 

usb gamepad circuit

Note: Optionally you can connect 2 more buttons to RB2 and RB3.

Code

Below is the PIC Basic code that works both on 18F4550 / 18F2550. (There are other requirements to build USB firmware including the HID header, see compiler documentation).

DOWNLOAD HEX FILE FOR PIC 18F2550 (You will need a PIC Programmer to transfer it to the chip, I'm using PICKit2):

18F2550_Gamepad.hex

IMPORTANT NOTE: Please disconnect any Microchip Devices (including the PICKit2 programmer) before plugging this device since it's using same HID VENDOR /PRODUCT ID provided in Microchip sample files.
If you plug 2 devices with same VENDOR/PRODUCT ID you might get a hardware conflict and the devices might not work.

—————————————————————————————-
Define  OSC     48
'CONFIGURATIONS ARE IN /PBP/18F2550.INC , YOU MIGHT WANT TO EDIT THEM

'ADC
DEFINE ADC_BITS 10         ' Set number of bits in result
DEFINE ADC_CLOCK 6        ' Set clock source  Fosc/64  => TAD => 1.34uS
DEFINE ADC_SAMPLEUS 50     ' Set sampling time in uS

TRISA.0 = 1
TRISA.1 = 1

ADCON1 = %00001101 ' sets AN0,AN1 to analog mode

ADCON2 = %10101110 '
    'bit 0-2: ADCS ,OVERWRITTEN BY ADC_CLOCK,  110: Fosc/64  => TAD => 1.34uS
    'bit 3-5: Aquisition time: 101: 12 TAD =>  16uS
    'bit 6: not used
    'bit 7: Right justify for 10-bit
    

x    VAR    WORD
y    VAR Word

INTCON2.7=0  'RBPU =0 , TURN ON PORTB PULL-UPS

bt1            VAR PORTB.0
                TRISB.0 = 1
bt2            VAR PORTB.1
                TRISB.1 = 1
bt3            VAR PORTB.2
                TRISB.2 = 1
bt4            VAR PORTB.3
                TRISB.3 = 1
    

'USB
buffer    Var    Byte[3]
USBInit

main:
    ADCIN 0,x    'read AN0
    ADCIN 1,y    'read AN1
    
    'x,y experimental measurments: ~512 @center / ~365 @ -90deg / -655 @ +90deg
    
    x = (x >> 2) << 2  ' clear last 2 bits
    y = (y >> 2) << 2  ' clear last 2 bits
    
    
    'convert x,y from range [384..512..639] to [0..128..255] with edge clipping
    x = ((x MAX 384) MIN 639 ) – 384
    y = ((y MAX 384) MIN 639 ) – 384
    
    
    buffer[0] = y    'gamepad's x-axis is accelerometer's y axis
    buffer[1] = x    'gamepad's y-axis is accelerometer's x axis
    buffer[2] = PORTB ^ %00001111 &    %00001111 'separate and reverse first 4 bits

    USBService    ' Must service USB regularly
    USBOut 1, buffer, 3, main  ' Send buffer to endpoint 1

GOTO main    ' Do it forever

—————————————————————————————-

Here is how it is detected by Windows XP. Please note that if you don't change the USB HID Vendor ID and Product ID code this device might conflict with other microchip HID devices using same indentification, including the PICKIT II USB programmer (you can't have them plugged in both at the same time).

control_panel_game_controllers.jpg

There's no need to calibrate the device on this Windows screen,  since it will output values within 0..255 range for both axis and it will be centered close to  128,128 values (we took care of this in the program).

However you might want to adjust sensitivity in your game, based on your preference:

sensitivity.jpg

Construction

If using an existing USB cable , the wire coding is VDD red, VSS black , D+ green , D- white.

Second prototype using PIC18F2550 chip.in a cheap Wii steering wheel shell. (Look for them on EBay they sell for about $1.45).

game pad built from a wii steering wheel shell

 

First prototype "THE BRICK" , using PIC18F4550 chip, accelerometer removed.

 

 

It can work as a motion MOUSE too !

 

With a slightly different firmware and  the same hardware you can build a USB Motion (Tilt/Pan) HID Mouse, source code is here:

http://code.google.com/p/hidmouse/

SVN Trunk:

http://code.google.com/p/hidmouse/source/browse/#svn/trunk/%20hidmouse

 

Also for anyone interested in a quick build, with all parts and PCB -  gamepad kits with pre-programmed PIC and accelerometer are available for  50 USD @  http://gadgetgangster.com/231 .


///starlino///