Demo:

About the project:

For the hardware I used the Acc_Gyro sensor and a thumb-size PIC platform UsbThumb built around the inexpensive PIC18F14K50 chip that provides all the necessary USB connectivity and ADC inputs.

This setup is actually hardware compatible with my original Motion Gamepad design so all the software utilities and firmware will work on the Acc_Gyro + UsbThumb combination that is available as a kit under the name of UsbThumbImu . The Acc_Gyro fits on top of UsbThumb and this is not a coincidence since UsbThumb was designed as microcontroller helper for the Acc_Gyro with the idea of being able to provide the USB/Serial/SPI/I2C interface, as well as making use of the built-in 10bit ADC module of the PIC18F14K50.

In the pictures above headers are used to connect the device, so the end result is a little taller  than you could get if you'd simply solder the two boards together. Both devices have been designed for people that would like to extend  or experiment with the existing solution so there is a second row of connectors on the UsbThumb that can be used to connect buttons or other devices to the project. 

All that's it for now – hope you liked the project. It was really easy to built having the two important components UsbThumb and Acc_Gyro. You'll find more info on individual components on my website as well as  on the GadgetGangster site with whom I partnered to provide kits for anyone interested. If you don't find the necessary information, or you have any any suggestions, ideas or questions – as always feel free to drop me a line with in the comment area below.

//starlino//

It is basically a customization of Mouse emulation demo that Microchip bundles with their USB Framework.

The code responsible for enabling/disabling mouse emulation is triggered by a timer interrupt like so:

        OpenTimer0( TIMER_INT_ON &
                 T0_16BIT              &
                 T0_SOURCE_INT         &
                T0_PS_1_256);

                     ………….

        //These are your actual interrupt handling routines.

        #pragma interrupt YourHighPriorityISRCode
        void YourHighPriorityISRCode()
        {
                //Check which interrupt flag caused the interrupt.
                //Service the interrupt
                //Clear the interrupt flag
                //Etc.
        #if defined(USB_INTERRUPT)
                USBDeviceTasks();
        #endif
       
                if(INTCONbits.TMR0IF){
                        counter_s++;
                        //to interrupt every 1s we need to count FOSC / 4/ 256  = 46875 ticks (0xB71B)
                        //to count these ticks till overflow we need to set TMR0 to  0xFFFF – 0xB71B = 0x48E4
                       
                        TMR0H = 0×48; //will write to TMR0H buffer
                        TMR0L = 0xE4; //will write actual TMR0L / TMR0H 

                        INTCONbits.TMR0IF = 0;
                }

        }       //This return will be a "retfie fast", since this is in a #pragma interrupt section

       ……………..

       INTCONbits.TMR0IE = 0;  //disable Timer0 interrupt
        if(emulate_mode && counter_s > 3){      // seconds on
                counter_s = 0;
                emulate_mode = 0;
        }else if (!emulate_mode && counter_s > 60){     //seconds off
                counter_s = 0;
                emulate_mode = 1;
        }
        INTCONbits.TMR0IE = 1;

For full source code see:

http://code.google.com/p/usbthumb/source/browse/#svn/trunk/UsbThumbMousePrank

UsbThumb is an open-hardware platform, anyone can build their own:

http://code.google.com/p/usbthumb/source/browse/#svn/trunk/Hardware

or pick up a prebuilt SMT version of UsbThumb here: http://www.gadgetgangster.com/303

In order to upload a new firmware to USBThumb you need to enter the bootloader mode. This is done by connecting the  VPP pin to ground during the time when device is plugged into the USB port.

This can achieved by placing a jumper wire or a 1K resistor (recommended) between GND and VPP pin.

GND pin is number 1, and VPP is number 5. Make sure you do not confuse VPP with the nearby VDD(pin number 4) or you will get a short !!! To be safe use a 1K or 10K resistor instead of the wire. Wire/resistor can be held by the spring action, it only needs to make contact during a split second while the device is plugged. If you plan on making frequent firmware updates , soldering a header is recommended.

Before plugging the device to USB port,  start the "USB HID Bootloader" application (it is installed as part of the Microchip USB Framework, look in C:\Microchip Solutions\USB Device – Bootloaders\HID – Bootloader), a copy is placed here for download:

HIDBootLoader.zip

Next insert the USBThumb into the USB port (with the VPP and GND pins connected) , you should see a "Device attached." message in the USB HID Bootloader window.

Next steps are simple:

1. Click on “Open Hex File” button and select the new firmware .HEX file you want to load
2. Click on “Program/Verify” and wait for the process to complete
3. Unplug the device from USB port. Remove the jumber wire/resistor between GND and VPP pin.
4. Plug the device back and verify the new firmware is working (it depends on firmware and what you expect it to do).

The pictures below illustrate the above steps:

A custom PIC firmware  comes preloaded on the
"USBThumb Propeller Programmer" available on GadgetGangster.com, it allows you to use USBThumb as a Propeller Programmer but also as USB to Serial converter.

USBThumb (loaded with USBThumbSerial firmware)  is detected on your computer as a standard  CDC Modem device and works on all modern operating systems (Windows, Mac os , Linux).

On Windows you might be asked for driver path once you attach the device, simply use the driver part of the Microchip's USB Framework (it can be found in C:\Microchip Solutions\USB Device – CDC – Serial Emulator\inf\win2k_winxp ) , and I am including a copy for direct download here:

microchip_cdc_win2k_winxp.zip

On Windows you can identify USBThumb's COM port number from Device Manager:

On Mac OS, once you attach the device  you will get a prompt "A new network interface has been detected". Look in the /dev folder. You should see it as "/dev/tty.usbmodem411" or similar.

PropellerTool can scan all available ports and find the one that has a propeller chip attached. So the above step might not be necessary, however if you already know the COM port of USBThumb you can specify it explicitly.

In the PropellerTool go to  Edit > Preferences>Operation and update the "Serial Port Search" to the port number of USBThumb (COM15 in my example). In the "Propeller Reset Signal" choose DTR.

Next attach the USBThumb to your Propeller development board, USBThumb's serial  4-pin connector is pin compatible with PropPlug. The pins are marked as follows RX,TX,RST,GND.

To test the communication with the propeller board press F7.

If you experience problems make sure the port is not open by any other software (like for example the propeller terminal software)

In some rare cases if you computer power supply is too noisy, to ensure greater stability you can place a 18pF filtering capacitor between pins 24 (RB5)  and 25 (RB6). See picture below:

You can solder the capacitor permanently between these pins, or if you're planning to use USBThumb for other projects and you have soldered sockets to the board simply insert the capacitor in the socket between pins 24 and 25. You only need to take this step if you have intermittent problems with PropellerTool not detecting the Propeller chip.

Release Notes / Change Log:

——————————————
2009-09-25
Config Utility Version 1.0.0
Device Firmware Version 1.5
——————————————

- device supports a wide range of accelerometers and gyroscopes
- implements smoothing filtering algorithm
- implements algorithm for combining gyroscope and accelerometer data
- HID USB interface makes the device compatible virtually with all modern operating systems (Mac,Windows,Linux)
- configuration utility (for Windows only for now)
- adjustable smoothing and scale factor for outputs
- configurable sensibility for accelerometer and gyroscope (can be set per axis)
- configurable midpoint (0g voltage) for accelerometer (can be set per axis)
- auto-find gyroscope midpoint (0 deg/s voltage)
- you can use separate accelerometer/gyroscopes for different axis
- Z axis not implemented in this release
- configurable analog input ports AN0-AN5 for each axis (please note 18F2550 does not have AN5 input , but 18F4550 does)
- ability to invert axis
- capture output and raw adc data into a comma separated values file (.csv)
- charting feature of all inputs/outputs
- graphical display of output and buttons
- supports up to 8 buttons
- configuration is stored in device EEPROM
- it is possible to use accelerometer alone on any axis (1, 2 or 3-axis) in this case set Smoothing to 0-10 value
- it is possible to gyro alone on any axis (1,2 or 3 axis) in this case set Smoothing to 100-255 , please note that the output will snap to middle after a while since gyro only provides rate information
- it is possible to use to use gyro and accelerometer on any axis (RECOMMENDED) in this case set smoothing to 20-100 value
- you can use multiple accelerometers or gyroscopes
- you can orient gyro or accelerometer as you like (but aligned to 90 degrees increments)
- you can connect your gyro and accelerometer outputs to any of the AN0-AN4 ports (for PIC18F2550).

Suggested Circuit Schematic

Below is a new suggested schematic , using a 2-axis Gyroscope and an a 2-axis Accelerometer. As mentioned above the new firmware and configuration utility is very flexible regarding the way the gyro and accelerometer are connected (this is one of the features requested , to be able to use device with various MEMS sensors).

Configuration Utility

Here is a screen shot of the configuration utility, please note that I am using the gyro just for one output axis (X), thus I set smoothing to 50 as recommended in release notes above. The other axis (Y) uses just accelerometer data so Smoothing is set to 5. Device automatically detected the Gyro midpoint to be 1.35V , you must hold device still for at least 1s to let it calibrate when you plug it in. The Gyro axis is also inverted due to the way it is mounted in the case.

Hardware Setup

My old accelerometer-only device , got modified to make space for a gyro. Here is how it all fit inside the case:

Demo

Finally here is a new demo with another game I found to work well with this device PURE. In this game you can actually use the FORWARD/BACK tilt (Y axis of the device), besides the usual LEFT/RIGHT (X axis) I demonstrated in the TMNations demos (see my first usb gamepad article).

Downloads

Configuration Utility Setup (Windows XP/Vista) StarlinoGamepadConfigSetup_100.exe

PIC18F2550 Firmware 18Fx550_USB_GAMEPAD_GYRO_15.hex (right click on the link and choose Save Link/Target As if HEX file opens in browser).

I will continue to edit this article , please let me know what questions/suggestions you have in the comments area below. I will try to update this page and design based on your feedback.

//starlino//

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 !

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).

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:

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).

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///