Flashback: Magnetic Stripe Reader

The central component of our project is a TTL magstripe reader. You don’t want one that’s advertised as being serial, parallel, keyboard, or USB based. Fortunately, TTL (also called “clock/data”) readers are much cheaper than other readers because they don’t contain circuitry for processing card data.

A TTL reader has three outputs: a card-present (CP) line, which lets you know when a card is being swiped; a clock (CLK) line, which goes high when the DATA line is valid; and a DATA line, which delivers a stream of ones and zeroes representing the data on the card. You will wire these signals to the pins of the game port. These pins are the same pins that joystick buttons use.

Basically, this reader “fools” your computer into thinking it is processing the activation of joystick buttons. First, the CP “button” is “pressed.” Then the CLK button is pressed, which saves the state of the DATA button. This allows the Stripe Snoop software to capture the entire bitstream contained on the card and decode it.

1a. Prepare the connector. The first step is pretty easy. Take the DB-15 male connector and place it in your helping hands. Take a wire from your jumper wire kit and place it in the other helping hand. Maneuver the wire so that it sits in the hollow part of the pin, and solder the end to pin 2. Repeat for pins 4, 7, 14, and 15. Pins 4 and 15 correspond to ground (GND) and 5V, respectively, while pins 2, 7, and 14 are the buttons used by joysticks. It’s easy to get turned around and forget which pin is which. Use a permanent marker to label the pins.

Next, cover the pins with hot glue to ensure the wires can’t pull loose or touch each other.

1b. Wire up the TTL reader. Use a knife to carefully remove the side panel that covers the Omron V3A-4’s circuit board. Cut the farthest right tab off of the cover (the tab the knife is pointing to in this picture). This hole is where our wires will come out.

1c. At one end of the circuit board you should see a row of nine metal contacts. We will be soldering wires to pins 1, 2, 4, 5, and 6 (Contact 1 is at the bottom and 9 is at the top as seen here). These contacts are rather small, and it’s easy to put down too much solder and short two of them together.

1d. Go slowly and make sure not to use too much solder. Check neighboring contacts as you go to make sure they don’t touch. Also check to ensure that you can see the white line in between them. If not, use the soldering iron to heat both contacts, remove the excess solder with a solder sucker, and try again.

This is the hardest part of the project. If you keep shorting the contacts together, try using the soldering iron to melt a small amount of solder onto the contact. It should bead easily and not touch the neighboring contact. Now, holding the wire in one hand and the soldering iron in the other, heat the bead of solder and push the wire into the liquid metal.

1e. Once each wire is soldered, carefully bend it 90 degrees and position it so that it exits the back of the reader where we previously removed the tab from the side cover. Use the hot glue gun on the bent wires when you are done to make sure they don’t pull loose. Be careful that you don’t use so much glue that you can’t see which wire is soldered to which pin. It is useful to fan out the wires (as shown) to keep the order correct.

Be careful bending the wires to ensure that you don’t pull apart the soldered connections. Use a pair of needlenose pliers to hold the wires steady at the solder joint before bending them with your fingers.

1f. Connect the reader and connector. The hard stuff is behind us. Now we simply join the DB-15 connector and the reader. Take your four-foot piece of Cat 5 cable and pick five wires you want to use. I recommend using all four of the solid color wires, and one of the striped wires. Strip off about 1.5 inches of insulation from each end. Cut off the three wires you are not using so that they don’t get in the way, and strip a quarter-inch off each of the five wires you are using. Do this to both ends of the cable.

We are going to connect the pins of the TTL reader to the pins of the DB-15 connector as indicated below.

1g. Use pliers to make small hooks at the end of each wire coming from the reader, connector, and cable. Hook the correct wires together and use a little bit of solder to secure them.

Use a small piece of electrical tape to protect each junction. Once complete, use more electrical tape to strengthen the transition at each end of the Cat 5.

While this step is not technically demanding, it is quite easy to make a mistake. It is very important that you solder the correct wires together. For each connection, I would solder one end of the jumper wire to the reader and the other to the DB-15 before moving on to the next wire. This helps prevent mistakes.

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.

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.

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.

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.

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!