Kaliko Systems Limited
Make a Low-Power Media Server
My Relay Boards
My relay boards consist of two 8 relay USB boards made by JBS, one 8 relay USB board made by Denkovi and one 8 relay parallel port board made by DIY Electronics.The JBS relay board is shown below. This British made board has 8 relays and has a standard USB 'B' socket for connection to a computer. The vendor has informed me that they have enhanced this USB board to now include 2 inputs, the USB socket has moved slightly and the USB power indicator LED (bottom left) is now behind the USB socket. The brown wires in the photo are my connections. The special feature of this board is that it is USB powered. The vendor rates the board relays at 6 amps for 250 Volts AC. This board is my personal favourite, but is not the best board for every use.
Note, on this board version the NO and NC labels on all the terminals are unfortunately reversed (my brown wiring has changed since this photo was taken).
The vendor's Web site is http://stores.ebay.co.uk/Affordable-Electronic-Parts
The Denkovi USB Relay Board from Bulgaria is shown below. It is a well made and there are good reports about it on the Web. This came well protected in good packaging (it included the beautiful Bulgarian Folklore postcard in the background).
The board has 10 amp rated relays and requires an external 12 volt DC power supply. The manufacturer states that the board can be used for 10 amp switching. The board is rather difficult for me to case, as it is can only fit with the USB socket at the top of the case and the relays are in an an odd order on the board. However, since it uses an external DC power supply it can be connected to low power USB devices. This board uses a FTDI chip to provide a virtual COM port USB interface and the vendor provides links to the standard FTDI drivers. The software is very comprehensive for Windows, Linux and MAC.
The vendor and board details can be found on Ebay by searching for "8 channel relay board" (but I cannot find a web site).
The first relay board I purchased was a parallel port kit (K74V2) and this is shown below. This Hong Kong kit is also sold by local distributors, and is very easy to build. You can also purchase it ready made, as a board or in a case with external terminal connections. I added the red wires and the wooden board you see in the photo below. The key feature besides the parallel port is the requirements for 12V DC (as parallel ports cannot provide any significant power).
My red wiring reflects two issues with using a parallel port board. The first issue is that booting with any Windows NT based operating system (e.g. Windows 2000, XP, Vista) turns all the parallel port data pins on. For mains switching, this can be overcome by using one relay's NC terminal as the live input to all the common terminals on the other relays. Similarly relays can be used in pairs, using NO and NC, for other applications. However, these "tricks" do not guarantee that there will never be an overlap for a few milliseconds when booting. The second issue is that many older parallel port extension cables only connect 7 output data pins, rather than 8. As I use such a cable and I use relay 7 for the above mains trick, this leaves me with 6 relays for equipment.
On one of my PCs the data pins get turned off automtically soon after they are turned on, but on another of my PCs they don't and I am not sure why. For the PC that doesn't clear the parallel port, the problem is that the LED indicators will show confusingly as on when the controlled equipment is off. To correct this, after booting I have a batch file automatically run from the Start/Programs/Startup menu to turn the relays all off. However, for XP there appears to be a race condition with the 16 bit application support starting, so you need to add a command to sleep for a few seconds before turning the LEDs off (search the Web for suitable sleep command for your OS).
You should be able to find a local distributor of this board, I purchased my one in the UK from http://www.quasarelectronics.com
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