Peter's electronic projects

USB digital GPIO I/O extender

description

Add general purpose input/output lines to your computer based projects. This circuit is a 12 pin digital GPIO interface using the Microchip PIC18f14k50 microcontroller which connects to an USB host port. The microcontroller is available in through-hole DIP20 and SMD packages, too.
NOTE for beginners: PIC18F14k50 is a general purpose microcontroller which has to be programmed before you can use it in the actual circuit! Please check out this link to learn more.

Circuit diagram

The device is powered by the USB bus. 12 port bits can be set on a bit-by-bit basis to input or output direction. All LEDs on the schematic are optional, and are only shown for testing the device. You can find the USB connector pinouts at http://pinouts.ws/usb-pinout.html

Interested in getting an assembled, pre-programmed, tested board? Check in my Tindie store

Controlling the GPIO interface

A computer, any OpenWrt router, Raspberry Pi or other Linux development board with an USB host port can be used to control the GPIO extender. The "controlio" utility runs on all platforms.

Usage: controlio [options] <command> [value]
Control an USB I/O port

 -d, --device <vendorid>[:productid]
    Select only device(s) with USB vendorid[:productid], default=0x04d8:0xf7c0
 -s, --serial <serial number>
    Select only the device with the given serial number, default=any
 -o, --output <base>
    Set output format. Base x=hexadecimal (16), b=binary (2), d=decimal (10), default=x
 -v, --verbose
    Verbose mode
 -V, --version
    Show program version
 -h, --help
    Show usage and help

The commands are:

Numbers for <vendorid>, <productid> and <n> can be given in decimal, hexadecimal or binary format. Hexadecimal numbers are prefixed with '0x', binary numbers are prefixed with '0b'. Command output base can be also set to hexadecimal with switch -ox, decimalwith switch -od or binary with switch -ob.

Mapping of I/O port pins, directions to parameter <n> and buffer output:

Examples:

0xf0ff

61695

0b1111000011111111

Download

Download drivers and utilities for the GPIO board for Windows, for others. The package contains:

Previous, obsoleted version with assembly firmware

Installing on the PIC18F14K50 device

Program the bin/device_firmware/usbio.hex file with a Microchip Pickit 2 or Pickit 3 programmer into the chip.

Installing on the host

Linux

1. install libusb-0.1 with "apt-get install libusb-0.1" or "yum install libusb"
2. copy bin/host/linux.x86/99-usbio.rules to /etc/udev/rules.d/ - this lets everyone use the device
   
3. copy bin/host/linux.x86/controlio to the host
4. connect the GPIO extender to the USB port

Raspberry Pi

1. install libusb-0.1 with "apt-get install libusb" on Raspbian or "yum install libusb" on Pidora
   
2. copy bin/host/linux.x86/99-usbio.rules to /etc/udev/rules.d/ - this lets everyone use the device
   
3. copy bin/host/raspberry/controlio to the host
4. connect the GPIO extender to the USB port

OpenWrt

1. install the package for your platform from bin/host/openwrt with "opkg install usbio_2.2-3_<platform>.ipk". This will also install the libusb package if not present
2. connect the GPIO extender to the USB port
   

Windows

1. Extract the contents of the directory usbio-v3.6/bin/host/win.x86
2. Connect the GPIO extender to the USB port
3. If your OS is Windows XP or Windows 7:
   the computer will ask for a driver – choose the driver.winxp-7 directory
   Go to step 8.
4. If your OS is Windows 8 or Windows 10:
   start the Zadig installer found in the driver.win8-10 directory
   The installer is signed by “Akeo Consulting”.
5. The bottom of the installer window should read "1 device found".
   If it reads "0 devices found" instead, please check the USB connection of the board and repeat from step 4.
6. Press the “Install driver” button
7. Wait for the message “The driver was installed successfully” to appear
8. Start the command line and enter this command:
   controlio -v getport
9. If the message “Matching device found.” is shown, the driver is operational

Testing

Check operation with "controlio getport". If everything is OK, a 16-bit number read from the I/O port pins is printed. In case of a "No matching device found..." error the GPIO extender is not found. The device is identified by the USB vendorid and productid. Check for the device with lsusb on Linux, cat /proc/bus/usb/devices on OpenWrt or in the device manager on Windows. Use the "controlio -v getport" command for troubleshooting.

Compiling the host side code under Linux

- install a C compiler and the libusb development headers

yum install gcc libusb-devel # for redhat/fedora/pidora
apt-get install gcc libusb-dev # for debian/ubuntu/raspbian

- compile the code

cd src/host/posix/controlio
cc -o controlio controlio.c -lusb

- check operation with the command

./controlio getport

Compiling the host side code for OpenWrt

- install the OpenWrt SDK on a computer
- copy src/host/openwrt/usbio into the package directory
- select the usbio package to be built (Utilities->usbio) from

make menuconfig

- build the usbio package

make package/usbio/compile V=s

Compiling the host side code under windows

- download and install mingw and msys from mingw.org
- copy the file from src/host/posix/controlio/controlio.c to the c:\mingw\msys\1.0\home\<user> directory where <user> is your user name
- download and install libusb-win32 from sourceforge
- copy include/lusb0_usb.h from the libusb package to c:\mingw\msys\1.0\include\usb.h
(if your libusb-win32 version is 1.2.4 or older, then copy include/usb.h to c:\mingw\msys\1.0\include\usb.h)
- copy lib/gcc/libusb.a from the libusb package to c:\mingw\msys\1.0\lib
- start the mingw shell from programs->mingw->mingw shell
- compile the code with

gcc -o controlio controlio.c /lib/libusb.a -I/include

- connect the USB device to the computer
- start bin/inf-wizard from the libusb package
- select the connected device from the list, then create and install a driver for it
- find the executable controlio.exe under c:\mingw\msys\1.0\home\<user> where user is your user name
- check operation with the command

 controlio getport

Programming the GPIO device from python

1. install pyusb package or download and install pyusb from http://walac.github.io/pyusb/
   

   yum install pyusb
   
   # or
   
   wget -O pyusb.zip https://github.com/walac/pyusb/zipball/master
   unzip pyusb.zip
   cd walac-pyusb-*
   sudo python setup.py install
   
   

2. install the libusb library/driver as described under "Installing on the host"
3. copy src/host/python/usbio_example.py to the host
4. play with the example code
   

USB requests

The circuit is a full speed (12Mbit) vendor-specific USB device. It uses only the control endpoint 0, and is controlled by vendor-specific control requests. If you want to make your own host interface, the implemented control requests are:

You can find the explanation of these USB requests (bRequest) and wValue <n> under "controlling the GPIO extender"

Planned improvements

• add analog A/D input capability to the firmware
• add SPI capability to the firmware
• add PWM output capability to the firmware
  
• add a command to the firmware to store default port states and directions to use on power-up

Please contact me if you need a feature, or have an idea.

related projects

• Multi-drop RS232/RS485 digital I/O extender at http://jap.hu/electronic/pbus.html
  
• The PIC source code is based on the USB framework written by Bradley A. Minch.
  You can find the original code at  http://pe.ece.olin.edu/ece/projects.html
• The USB framework was ported by me to the PIC18f14k50. The ported code is at http://jap.hu/electronic/pic18-usb.html
• Teensy, an Atmel AVR based board for similar purposes
  

References

• Microchip PIC18F14k50, PIC18f13k50 microcontroller datasheet
• OpenWrt, Linux for embedded devices
  
• USB connector pinouts
• USB made simple, tutorial
• USB in a nutshell, tutorial
• USB Complete - The Developers Guide, Jan Axelson, book
  
• USB Design by Example, John Hyde, book
• wireshark, monitor USB packets