Picture 1 (source: http://mindstormsnxt.blogspot.com/2006_08_01_archive.html
) is a diagram of the pinouts for for the NXT motor.
Here's a description of the pins:
1 Motor signal 1 (from 0 to 9V)
2 Motor signal 2 (from 0 to 9V)
4 Encoder power (5v)
5 Encoder signal 1 (0 to 5V)
6 Encoder signal 2 (0 to 5V)
To Drive the NXT motor you only need to work with pins 1, 2, and 3. Pin 3 is ground, or negative (-). If you supply 3.3 volts from the Trakr to pin 1 and zero volts to pin 2 the motor will turn in one direction. Conversely if you supply zero volts to pin 1 and 3.3 volts from the Trakr to pin 2 the motor will spin in the other direction.
There are a number of methods to make a conversion cable to connect from the NXT to the Trakr availalble on the web and there are some companies who specially make conversion cables. I, however, did not wish to cut up my NXT cables because they are kinda pricey. So, this was one of those "What would Macgiver do" situations.
Fortunately there was a new business moving into the building where I work and building maintenance was doing some construction on the offices. Maintenance had thrown out those combination network and telephone wall jacks and I grabbed a couple to toss into my spare parts box.
Many office telephone systems use six wire modular telephone cords rather than the standard household two wire cords. Thus, the wall jacks had an RJ45 network connector and an RJ12 telephone connector (six wire modular connector). Now I have a method of interfacing the NXT motor to the Spy Video Trakr circuit borad header pins.
If you look at picture 2 (source: http://www.philohome.com/nxtplug/nxtplug.htm
) you will notice that the RJ12 connector and the NXT connector are slightly different. The clip that holds the connector in is in the middle of the RJ12 connector, but on the NXT connector it is on the right of the connector. In my information technology work I have found that these clips often break off, but the connector is still usable. So, I broke one of the clips off one of the connectors on my NXT cable and filed the remaining plastic down so it would fit snugly into the RJ12 plug.
I removed the RJ12 plug from the wall plate. See pictures 3, 4, 5, and 6.
Next I created a hole through the plastic cover. I cut out the entire "R" in TRAKR including the drop shadow and this makes the perfect sized hole for the RJ12 plug. See pictures 7 and 8
To make the connection between the RJ12 connector and the header pins on the Trakr circuit board, I took and LED connector from and old computer (it was the "turbo" indicator to give you an idea how old the computer was) and cut the wires to the LED connector. I punched down the black wire into the pin 1 punch down on the RJ12 connector and the yellow wire into the pin 2 punch down on the RJ12 connector. See pictures 9, 10, 11, 12, 13, and 14
Now you are ready to put the plastic cover back on the Trakr. See picture 15.
I punched down the Snap Circuits jumper wire that is connected to the Trakr's ground on the circuit board (see step 4) to pin 3 on the RJ12 plug as close to the snap as I could which forces the snap to be on the outside of the plug since there is no room to fit the snap on the inside of the plug. The Snap Circuits jumper wire was thicker than the LED wire so, it was a little harder to punch it down. The I connected the LED header connector to pins GPIO 0 and GPIO1 on the Trakr's circuit board. See picture 16.
I replaced the plastic Trakr cover. I plugged one end of the NXT cable--the one where I did not break off the fastening clip--into the NXT motor. I plugged the other end of the NXT cable the one where I DID break off the fastening clip--into the RJ12 connector on the Trakr. See picture 17.
Finally added the Lego cargo deck to the Trakr and connected the NXT claw attachment. See pictures 18, 19, 20, and 21