With the rapid progress in computer technology many people now have a surplus computer just gathering dust somewhere. Thus these computers are free to be used as dedicated controllers for a variety of uses: turning on/off lights or other devices around the home, office, laboratory or factory come to mind. All that is needed is the interface to connect the QK165 to the real world. This relay card provides both the hardware and the software to do this. The hardware plugs in directly to the parallel port of the computer. It carries 8 relays. Each relay is switched on or off by one bit of the output byte which usually goes to your printer to print a character. The relays are rated to switch 250VAC at 7A. However, because of the PCB track thickness and width we do not recommend using the relay to switch more than 5A. If you want to switch more current then we suggest you solder some heavy duty wire links, on the bottom of the PCB, from the relay contacts to the screw terminal block (effectively in parallel with the PCB track).

HARDWARE It contains eight identical switched relay positions, power input positions to the relays (2.5mm jack centre positive) and a DB25 connector to the parallel port of a PC. Use a straight-through 25 pin cable (DB25 male at one end, female at the other) cable from the PC to connect to the Kit. To keep the kit simple no input latches have been put on it. If your application is important then you should use a UPS to keep the computer operating in the case of a mains power supply failure. The relays are under direct control of the output byte (8 bits) from the parallel port. When a pin is high a nominal 5V is presented to the input of IC1, ULN2803A an 8 channel high voltage, high current darlington transistor array, used here as a relay driver. There are a number of different types in the series - the 2803 is directly compatible with TTL and CMOS logic when operating at a supply voltage of 5V. The output is 'open collector' and features built in diode protection, making it ideal for use as a relay driver. Each relay is connected between the output pin and +12V. When the input is high the corresponding output goes low and the relay operates.

DOS Utilities. The k74_dos.txt file give full details on how to use these DOS files in batch files. Of course, you can write your own programs in any language to output a byte to the printer port and the bits which are high will turn on the corresponding relay. The overlay on the PCB shows which bit in the output byte turns that particular relay on. For example, output 00010001, or 11 in hex turns on relays 1 & 5. Each relay number is also marked on the overlay for easy reference.

Windows 9x/2000/NT/XP. After you run setup read the drivers.txt file and follow the instructions. Put an icon on your desktop of the diyk74.exe. Play with the program and you will soon learn how it works. Time files can be saved. Read the Help file for more information.

Linux software for Kit 74 has been written by James Cameron. You may get it at Quozl's Open Source Work. http://quozl.netrek.org/

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