One of the simplest examples of a new device is a light, or buzzer.
The simplest way to connect one or more lights, buzzers, bells, or whistles, or other simple devices to your computer, is through the parallel port.
Later in this course you will learn how to open up your computer, and connect directly to the bus of your computer. For now, however, we will begin with just connecting something to your parallel port, so that you do not have to open up your computer just yet.
Also, you can make a device that can be plugged into various different computers.
Being able to make your own devices is a useful skill that will allow you to invent new devices that are not available yet commercially.
One example of a device that is not YET available commercially, is a Licensed Seating Chair for preventing theft of Seating Services (TM). This chair plugs into the parallel port of almost any computer, allowing carpenters to continue to receive payments for seating, just as musicians continue to receive payments for music produced long ago. A simple parallel port device driver, called ``paraseat'' was written for the seating License Server, so that users can download, over the internet, a license to sit.
Here is the wiring used for the internet chair:
pin number use seatwire default_volt_dec_alpha x86dos x86gnux
computer's +5v power red
13 in 5 sltc
25 ground black
12 in 5 pe
24 ground
11 in 5 -busy
23 ground
10 in ck(IRQ 7) yel 5 ack
22 ground
9 d7 spikes retract when hi.21
21 ground
8 d6 buzzer when high .21
20 ground
7 d5 .21
19 ground
6 d4 .21
18 ground
5 d3 .21
17 io -slct_in
4 d2 .21
16 io init (out)
3 d1 .21
15 in error (in)
2 d0 green .21
14 io -auto_fd_xt (in)
1 io 5
Notice that there are 25 pins on the parallel port, many of which are
(redundant) grounds.
There are 8 data lines, 4 IO lines, and 5 input lines.
Therefore you could connect up to 8+4=C (12, baseA) lights up to the parallel port. You could also connect up to 8+5=D (13, in baseA) switches, to use as inputs.
Here I have connected a credit card reader, a buzzer, and various items such as a solenoid to retract the spikes in the seat.
The simplest test-case is just to connect one or more lights to the parallel port. Eight is enough to test the general spirit of connecting something up.
Connecting up some LEDs on your parallel port to make your LED pushbroom