Project : CH341A relay board, simple control from PC or Raspberry PI
Using Inotify : Create file: turn relay on

Using just plain linux and libusb-1.0 control the relays
This document was written by Edwin van den Oetelaar, please leave my name intact.

Building the software:
- have gcc/make etc installed
- run make
- done

Connect the board using a usb cable.
Make sure you have enough rights to control the USB device 
(see if it is present with lsusb command)
$ lsusb
Bus 002 Device 024: ID 1a86:5512 QinHeng Electronics 

If you need to run the board as a normal user you need to a a rule to udev to allow it
My group was 'oetelaar' make sure you set up your group correctly, not my group name!! 

$ cat /etc/udev/rules.d/60-OETEL-IOSOLUTION-ABACOM.rules
# start of file 
    ACTION!="add|change", GOTO="isp_rules_end"
    SUBSYSTEM!="usb", GOTO="isp_rules_end"
    ENV{DEVTYPE}!="usb_device", GOTO="isp_rules_end"

    # de IOsolution USB board
    # Bus 002 Device 006: ID 07a0:1008
    # no longer sold
    ATTR{idVendor}=="07a0", ATTR{idProduct}=="1008", MODE="660", GROUP="oetelaar"

    # new device, ABACOM relay board based on CH341A chip in MEM mode
    ATTR{idVendor}=="1a86", ATTR{idProduct}=="5512", MODE="660", GROUP="oetelaar"

    LABEL="isp_rules_end"
# end of file

Usage Examples: 
run as root if you do not have udev set up correctly

$ sudo ./switch_relay 1 2

$ switch relay 1 and 8 on, rest is off (and as normal user)
$ ./switch_relay 1 8 

=== detailed usage ===
Name : switch_relay - switch relays on Abacom or Elomax board on or off
Can be run once, to set some relays or
can run as a directory monitor using inotify, will switch relays when files are created or removed

switch_relay [options] [relay_number] [relay_number]
options:
 -s : use syslog for logging instead of stderr
 -d : keep running (as a daemon) does not fork (use something like supervisord)
 -i <directory_name> : use event listing on this directory instead of /tmp
 -h : show help text
 -m <0|1> : use Abacom=0 (default) or Elmax=1 protocol and device
 -z loglevel : set loglevel (default=7) valid levels : ERR = 1, WARN =2, NOTICE=4, INFO=8, DEBUG=16 OR together


Usage example:
 $ switch_relay  : switch all relays off
 $ switch_relay 4 : switch all relays off, but switch relay 4 on
 $ switch_relay -s -d -z 31 : use syslog, keep running, use maximum logging

When using (-d) the program will monitor /tmp/ for creation or removal of files
 /tmp/D_OUT_1 /tmp/D_OUT_2 .. /tmp_D_OUT_8
 create a file with that name and the output will be active (on) remove the file and the output will deactivate (off)

example :
 $ touch /tmp/D_OUT_1 : will active relay no 1
 $ rm /tmp/D_OUT_1    : will switch relay off again



Board can be bought here:
http://www.electronic-software-shop.com/hardware/relais/usb-relaiskarte-lrb-8-fach.html

Pro: not expensive, ships in couple of days.

Cons: 
- small relays, 
- no LED when board has power (bad!) 
- or LED when Relay actived   (bad!)
- no way to see what is happening
- The software is old windows DLL only (bad!) 
- no documentation on how it works, no schematic. (bad!)
- no way to read the actual state of the registers on the board (not yet)

More info about the chip used:
http://hackingbtbusinesshub.wordpress.com/category/ch341a/
http://www.winchiphead.com/download/CH341/CH341DS1.PDF
http://www.winchiphead.com/download/CH341/CH341DS2.PDF
Use google translate to read it, it is in Chinese.

The relay board works in MEM mode of the chip.
The data is shifted into the register bit by bit, clock by clock using a (too) complex USB protocol
The data is moved into a shift register which looks like this A6275EA
I found a datasheet here: http://www.jameco.com/Jameco/Products/ProdDS/1719228.pdf

In theory multiple shift registers could be cascoded to form a very long register with many outputs.

Hope this helps someone, 
If something is wrong or missing, sorry no garanties by me, I am just a guy sharing his findings.

Greetings,
Edwin van den Oetelaar

PS,NB. be careful, make sure failure of the software or board can not result in harm to anyone!!