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https://github.com/daniel-thompson/rfstompbox

Circuit diagrams and software for a USB foot switch using an ATTiny microcontroller.
https://github.com/daniel-thompson/rfstompbox

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Circuit diagrams and software for a USB foot switch using an ATTiny microcontroller.

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README 

        
README

======



RFStompbox is a USB keyboard with just one key, albeit a multifunction one.

It is designed to be built with a foot switch and a strong case in order to

provide foot operated control for a computer.



It can be used:



- to start and stop playback of backing tracks

- to engage/disengage software implemented effects

- to switch patches or presets



At power on it acts as a space bar (without auto repeat) but by holding down

the button for a second then other modes can be selected.



FILES IN THE DISTRIBUTION

-------------------------



Readme.txt ........ The file you are currently reading.

circuit/ .......... Diagrams of the circuit.

firmware .......... Source code of the controller firmware.

firmware/usbdrv ... USB driver -- See Readme.txt in that directory for info

License.txt ....... Public license (GPL2) for all contents of this project.

Changelog.txt ..... Logfile documenting changes in firm- and hardware.



COMPILING AND INSTALLING

------------------------



This project can be built on Unix (GNU/Linux, FreeBSD or Mac OS X) or Windows

although no testing has been done on any platform except GNU/Linux.



Building on Windows:

You need WinAVR to compile the firmware. A package can be downloaded from:



    WinAVR: http://winavr.sourceforge.net/



To build the firmware with WinAVR, change into the "firmware" directory,

check whether you need to edit the "Makefile" (e.g. change the ISP upload

tool) and type "make" to compile the source code. Before you upload the code

to the device with "make flash", you should set the fuses with "make fuse".



Building on Unix (GNU/Linux, FreeBSD and Mac):

You need the GNU toolchain and avr-libc to compile the firmware. See



    http://www.nongnu.org/avr-libc/user-manual/install_tools.html



for instructions on how to install avr-gcc and avr-libc.



To build the firmware, change to the "firmware" directory, edit "Makefile"

to use the programmer of your choice and type "make" to compile the source

code. Before you upload the code to the device with "make flash", you

should set the fuses with "make fuse".



MODES OF OPERATION

------------------



At power on the system enters mode 1:



Mode 1:

This mode is designed for standard software where the space bar toggles

on/off controls (e.g. a checkbox in a GUI) or toggles play/pause

controls (common in media player).



  Single click     -> Send "Space"

  Double click     -> Disabled



  Hold button down -> Switch to mode 2



Mode 2:

This mode is desinged for the guitarix or gx_head amp modelling software.

It can be used to engage/disengage an effect (single click) and also to

change presets (double click).



  Single click     -> Send "Return"

  Double click     -> Send "Return", "Return", "1" or

                      Send "Return", "Return", "2" (toggles)



  Hold button down -> Switch to mode 1



It is possible for anyone with a ICSP programmer to add new modes. See

source code (or contact author) for more information.



HARDWARE

--------



RFStompbox is a member of a family of simple platforms contructed from

Atmel's ATTiny85 microcontrollers. All family members share the same USB

pins and these pins have been carefully selected to avoid using pins

that are needed for in-circuit programming (ICSP). This allows them to be

reprogrammed without disconnecting them from the computer that supplies

them power.



The RFStompbox differs from the standard platform by using diodes instead

of a voltage regulator (not required to monitor a switch) and by connecting

the switch directly to the main board (rather than a daughterboard hanging

off the ICSP connector).



USB communications using software bit-banging (thanks to Objective

Development's V-USB driver). Strictly speaking this circuit does not

meeting the USB electrical specification but is close enough to work with

almost all USB hosts. It also uses the USB host clock to callibrate the

ATTiny's internal oscillator eliminating the need for an external crystal.



Two diagrams of the circuit are supplied. The first, rfstompbox.pdf, shows

the full circuit complete with the ICSP port to allow the firmware to be

updated. The second is functionally equivalent but does not include the

ICSP port meaning that the the microprocessor must be removed from the

circuit for firmware updates.



Note: The striped down circuit has a deliberately inefficient design

      (in terms of board space, redundant cut tracks and the use a wire

      where a jumper could be used instead) in order to allow an ICSP

      header to be retrofitted to an existing build.



The result is a very cheap circuit to build. Have fun.



MORE INFORMATION

----------------



RFStompbox was written by Daniel Thompson using driver software and

example code from Objective Development. For other projects by the same

author see:



    http://www.redfelineninja.org.uk/



Flip van den Berg's 1-key keyboard source code was used as "scaffolding"

whilst developing the firmware for RFStompbox although none of his code

still appears in the final release.



    http://blog.flipwork.nl/?x=entry:entry081009-142605



For more information about Objective Development's firmware-only USB driver

for Atmel's AVR microcontrollers please visit the URL



    http://www.obdev.at/products/vusb/



A technical documentation of the driver's interface can be found in the

file "firmware/usbdrv/usbdrv.h".