RS-232 General Purpose Interface

1. Parts list

2 bi-colour light emitting diodes
2 chrome panel-mount LED bezels
1 momentary switch
1 clip-on 9V battery holder
1 jiffy box with internal PC board
1 female DB25 plug
1 DB25 hood
1 roll of hook-up wire
1 9V battery
1 to 2 metres of telephone cable

2. Connection

Input stage

Firstly, strip the white and brown leads. Push these through the PC board. Then, connect the battery holder's negative (black) lead to whichever colour lead is connected to pin 6 (probably brown). Connect pin 2 to one pin of the momentary action switch and the positive wire to the other.

Connect a 9-volt battery and proceed to test with a multimeter before connecting up to the computer.

Output stage

Attach the two LEDs to an unused section of the PC board. Try to keep it seperate from the input stage, to assist in faultfinding (sic), and also for safety reasons.

Then, using hook-up wire, attach the LEDs to the orange and blue wires in reverse polarity. In other words, the long pin of one LED should be wired in parallel with the short pin of another LED.

Tes t by applying current to the PC board, or by sticking wire into pin 3 and 6.

3. Software

I have written two programs, Sender and Receiver, that make use of the project.

As the I/O share common ground, please do not try to make multi-tasking programs!

4. Mounting

Drill holes for the bezel in the box, but be extra careful not to drill the posts for mounting the insulated lid and PC board. Mount the bezel at the front or the top, and the momentary switch on the side or top.

Don't forget to make an entry for the cable before soldering it to the PC board, unless you want to drill a semi-circular opening at the bottom.

Luke Howard and Joshua Reich