Flashback: Magnetic Stripe Reader – Make:


So what do you do if your computer doesn’t have a game port? Well, as long as you have an available parallel port, you can build a simple adapter that allows you to use the reader we have constructed.

The adapter makes use of the five inputs used by printers to report errors to the PC. Instead of checking if the CLK joystick “button” is pressed and saving the status of the DATA button, we are checking to see if the printer is out of paper, and then saving the status of the acknowledge pin. We use a buffer/line driver chip between the game port and the parallel port to protect against future readers that might produce too much current and damage the parallel port. We also need a 5V power supply because the parallel port doesn’t have one.

2a. Prepare the project box. Use a Dremel tool to cut the holes in the project box. I’ll refer to the face where the metal plate goes as the top of the box. Place the box top down, so you are looking at the bottom face, with the short sides to the east and west. On the east side of the bottom face, drill a 1″ hole. This is for our battery leads.

This is going to be messy! Do this in a place that is easy to vacuum. Wear eye protection against the flying plastic pieces.

Now, on the west face of the box, near its edge with the bottom face, cut a hole for the DB-15 connector. It should just fit between the two screw posts. Remember: don’t glue any of these components in yet!

On the south face (a long side), near the edge it forms with the bottom face, cut a hole for our DB-25 connector. We want this hole to be close to the west side of the face, about ½” from the edge the south and west faces make. Again, use the Dremel to cut a hole and then shape it until the DB-25 connection fits.

Finally, we need to cut holes for our power switch and power LED. These go on the east face, near the edge the east and bottom faces make, Drill a 1″ hole for the LED’s wires, and use the Dremel to make a small hole for the power switch.

2b. Prepare the connectors. Next we need to prepare our DB-15, DB-25, power switch, and LED. Since these components will be mounted to the project box, it’s important the wires we solder to them are long enough for us to comfortably solder them to the circuit board. You should use the longer wires in the wire kit. We are going to solder long wires (the red wires are a good length) to pins 2, 4, 7, 10, 14, and 15 on the DB-15 connector. After you’re done, use the hot glue gun and cover all the pins and wires.

The pin numbers on the DB-15 female connector are the reverse of the male connector. Use a permanent marker and note which pins are which! Do the same for the DB-25.

Solder wires to the DB-25 pins 10, 11, 12, 13, 15, and 25. Again, use the longer wires to give yourself enough slack. Use the hot glue gun to cover all exposed metal on the back of the connector.

For the power switch and LED, solder wires to the leads on both. Make sure you remember which wire is attached to the shorter lead on the LED. This wire will later be connected to GND.

2c. Make the power supply. The power supply should be located on the left side of the circuit board. Don’t worry about soldering on the battery leads yet, so be sure to leave some space to the left of the power supply. Use the shortest wires from the wire kit: red, orange, yellow, and green. When connecting components, twist the leads together using a pair of needlenose pliers. The circuit is rather straightforward, as shown in the diagram.

There are a lot of connections to the power supply’s outputs (especially GND) so leave room around them. Try not to have more than four wires at each junction. As you need to, use short red wires to extend a junction for additional wires. Note that the lead on the capacitor closest to the off-color stripe, or the lead that is the shortest, should be connected to GND.

Hint: If it makes you more comfortable, build this circuit on a breadboard first. Then implement it in stages.

2d. Attach the octal buffer, final preparations. With the power supply on the left of the circuit board, place the 74541 chip on the right side of the board, with about five holes open to its right. You should also place the chip upside down (pin 1 at the bottom). This places our input pins (pins 2-5) on the right, where the DB-15 connector will be.

Solder the 5V and GND wires to the pins as shown. Attach the resistor to a 5V line and leave the end open. We will connect this to our power LED.

Bend the unused pins on the 74541 to help hold the chip to the board while soldering. Just make sure you don’t let any of them touch.

2e. Final construction. Now we attach the wired connectors to the circuit board. Push the power switch into its hole, with the wires going into the box. Use hot glue to secure it in place. Do the same with the LED. Slide both leads from the battery-clip thru hole in the bottom face and solder the black wire of the battery clip to the GND input of the power supply. Solder one end of the power switch to the 9V input of the power supply and the other to the red wire of the battery clip. Solder the wire on the short side of the LED to the GND and the other to the resistor.

Next, glue the DB-25 connector into place. Solder the pins to the correct pins of the octal buffer using the circuit diagram. Remember, the octal buffer is upside down; all the DB-25 wires should connect to the side of the chip facing the power supply. Solder them according to the diagram.

Finally, slide and glue the DB-15 connector into place. Things are probably getting crowded, so use needlenose pliers to help move the wires into position. Solder them according to the diagram.

Don’t use too much glue with the power switch, or you could glue the switch into one position. Things will get difficult as you attach the wires from both DB connectors. Make sure in all the mess you don’t short anything out.

Usage and notes

Sometimes, if the adapter is connected to the parallel port and the battery is not connected, the power light will still be on. I’m still not entirely sure why this happens. Depending on the amps needed to run your reader, it may even function. However, to guarantee the results, use a battery. The circuit will also operate without a buffer chip. However, it’s better to fry a 50-cent part than your parallel port. Use the chip.

Please note

A black box with wires coming out of it, a switch, and a red light tends to worry airport security. You have been warned!



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