The data line of the parallel port can provide between 0 and 5 volts. Therefore, we can use this line to control a relay and let that relay control an electrical device.
Use pins 2 through 9 to get +5V
Use pins 18 through 25 as the Ground
____________________________________________________________
/ \
\ 13 12 11 10 9 8 7 6 5 4 3 2 1 /
\ /
\ 25 24 23 22 21 20 19 18 17 16 15 14 /
\______________________________________________________/
| Vcc for Relay
|
|
/ -------+--------| |---------|
P data 4.7K B / c | 1N4002 |_| |-------
-----------/\/\/\/\---------+-----| NPN _____ | relay |home device
| \ e /_\ |-| |-------
LED X \ +--------| |---------|
P Ground | | |
----------------------------+-------+--------+
Relay Ground |
---------------------------------------------+
|
Below is the key to the diagram above:
P data parallel port data line(pin 2 to pin 9, use any) P Ground parallel port ground (pin 18 to pin 25, use any) Vcc depends on the type of your relay. I'm using 12VDC Relay Ground the ground for 12VDC 4.7k 4.7K resistor NPN C2235 NPN transistor 1N4002 1N4002 diode LED light emitting diode relay a coil relay |
+5 volts from parallel port will turn on the relay. Once the relay is on, the device connected to that relay will be on. When the parallel port's data line goes back to 0, it will turn off the relay, and device is off.