Assuming this is the product you have, have a look this customer comment who has graciously left some breadcrumbs on how to control the device. As some other customers have noted, the product cycles (ON/OFF) the relays on power up and also malfunctions in certain cases you might want to take the right precautions when using it in your application.
There is download link below the comments to a rar file that contains some documentation and device drivers for windows
Here is an extract from the documentation
8 SPDT relays SRD-12VDC-SL-C
Relay specification – 10A 250VAC/10A 125VAC/10A 30VDC /10A 28VDC
Power Supply - 12 VDC
Current consumption - 300 mA
FT245RL. Datasheet –( http://www.ftdichip.com/)
Led for each relay output
Size - 93mm / 70mm / 16mm
Supported by DRM Software
Windows software examples: VB6, BCB6, Java (netbeans), VB.NET 2010 Express,
C++.NET 2010 Express
PCB parameters: FR4 / 1.5mm / two layers / metalized holes / HAL / white stamp / solder mask
Extra PCB openings for better voltage isolation
Doubled high current tracks
When the board is connected to the PC and the PC is restarted, the relays will
be toggled several times. This is because of the structure of the FTDI chip.
The device must be supplied with 12 VDC or order to work.
There is no protection against reversed voltage! If the VCC(+12V) and GND are
reversed the board will be damaged!
The board can not work without computer
Briefly (incase the link(s) go dead sometime) the relay board appears to use a FTDI chip (USB => USART) and therefore should be simple to control by writing to the serial port like so (taken from a customer's comment on amazon and modified to include more examples)
s = serial.Serial(port='COM15', baudrate=9600, bytesize=serial.EIGHTBITS, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, timeout=None)
s.write([b'\00',b'\00']) # all off
s.write([b'\xFF',b'\xFF']) # all on
the protocol appears to be
<mask> <value> where
<mask> is a 8 bit number, with relays corresponding to bits set 1 get affected by the value
<value> is a 8 bit number, 0 turns off, 1 turns on
so talking in hex,
0a should affect the first 4 relays (
0f), turning relays 4 and 2 on and 3 and 1 turned off.