From Opendildonics.org

Building a Parallel Port OpenDildonics Computer Interface

Contents 1 Overview 2 Procedures 2.1 Parts 2.2 Connecting the relay to the DB-25 connector 2.3 Connecting the relay to your vibrator 2.4 Additional notes

Overview

The Parallel Port OpenDildonics Computer Interface (ODCI) is a simple set of electronics that allows you to control multiple on-off type OpenDildonics devices. It will not able to control PWM devices, so if you need an interface to control PWM devices or both PWM and on-off devices, you should consider building a USB Computer Interface since those can be easily adapted to work with on-off devices as well. There is a newer design at Motor_Control_I that is solid state and has better parallel port protection, and is only slightly more complex to construct. In addition, that design can be made to do software PWM, or recycled to take its control signal from a microcontroller

Procedures

The steps involved in building a Parallel Port OpenDildonics Computer Interface are as follows:

Parts

You need three components to assemble the Parallel Port Computer Interface: a male DB-25 connector, a normally open (NO) reed relay that can be triggered with a 5-volt signal (such as Radio Shack PN: 275-233), and a length of wire. You'll also need standard tools like a soldering iron, solder, wire cutters and something to hold your components in place while you solder them.

Connecting the relay to the DB-25 connector

Solder one lead to Pin 2 on the DB-25 connector and the other to Pin 18. These leads are then soldered to the coil pins on the reed relay. On a Radio Shack SPST-12VDC Reed Relay (PN: 275-233) the coil pins are located on the side of the relay that has three pins. The two pins opposite each other on that end are the coil pins. Polarity isn't important here, so attach one lead to one pin and the other lead to the other (don't worry about positive and negative on the relay - it doesn't care).

If you are not using a disposable parallel port, adding a diode for port protection is probably a good idea. The diode will protect the port from damage from high voltage spikes created by the relay's windings. Any cheap silicon rectifier diode will work, such as a 1N4001 or 1N4007 or (for better protection) a 1A power schottky diode like the 1N5819. This should be wired in with the band end facing the wire which goes to pin 2.

Connecting the relay to your vibrator

You should now have two bare pins, one at each end of the relay. These are the pins for your normally open circuit. Take the two leads from your OpenDildonics on-off type device and solder one lead to each of the remaining pins on the relay. Again, the polarity of the connection isn't important.

If you'd like to interchange your devices and not have to assemble multiple computer interfaces, you can instead solder these leads to the socket end of a connector like a 2.5mm Phone Jack (Radio Shack PN: 274-245) and then solder the plug end of a 2.5mm Power Plug (Radio Shack PN: 274-289) to the leads coming off of your OpenDildonics on-off type device.

Additional notes

If you want to control more than one device at once with a parallel port, connect a second wire to Pin 19 for ground, and a wire to Pin 3. You can control up to 8 OpenDildonics devices with a parallel port by using pins 2-9. Each of these pins needs to be paired with a pin from 18-25 (ground) and connected to a separate circuit like the one described above.

Software control information and a full description of the voltage levels and properties of parallel ports can be found at Beyond Logic