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This is the A-head
Part II: More Hacking Techniques
While inspecting a prospective building, take some quick measurements
for the total length of wire you will need.
2. Install the digital I/O card
Control of the Blinkenlights pixels comes from one or more parallel I/O
cards. The software runs on top of the Linux operating system and uses
the drivers for cards based on the Intel 8255 parallel I/O integrated circuit.
Here are several potential vendors for these cards:
· Webtronics (
http://www.web-tronics.com/) offers the ACL-7122 144-
port ISA card. This card contains all of the necessary ports so you only
need one.
· Kontron (
http://www.kontron.com/) also offers ISA cards based on the
8255 chip.
· A German company called Decision Computer (
http://www.decision-
computer.de/) offers an ISA card with 192 ports (Part #82192V).
The card will most likely come with a flat ribbon cable that plugs into a
connector to bring the 144 digital outputs to the outside of the PC. You
may need to remove one of the expansion slot covers to allow the cable to
escape.
Install the card(s) in an unused ISA slot in the PC that you intend to use as
the main controller.
3. Build relay drivers
The digital output board is unable to directly drive the lamp relays by them-
selves. A relay driver must be built for each lamp. The relay drivers are in
turn driven by the digital output board.
The members of the CCC built their own relay drivers and relay boards.
The relay drivers were located next to the controlling PC, and actual relays
were located next to each lamp. This made the system safer by keeping all
high voltages away from the controlling PC.
Construct 18 relay driver boards according to the schematic diagram in
Exhibit C
. Build your relay drivers in groups of eight to keep the size of the
individual circuit boards smaller and make it easier to troubleshoot and
fix. When you have completed this step, the boards should look like those
in
Figure 8-8
.
You may instead want to buy the relay drivers with the relays included.
WebTronics (
http://www.web-tronics.com/) carries an 8-port relay board
with drivers (Part #Kit-74) for about $33. You will still need to purchase
and assemble 18 of these, but it can save time over building drivers from
scratch.
Figure 8-8: Relay drivers