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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