Hacking the LEGO NXT

As the LEGO NXT is more complicated than the RCX; I had to do my own research to be able to hack the NXT connectors. Here is some interesting information about the signals from LEGO Mindstorms NXT. (8/2/2007)


If you are a millionaire and able to buy a LEGO Mindstorms NXT, you may find kind of difficult to hack it or create homemade sensors.


ntx connector I believe you already noticed the particular jack that comes with the NXT. It looks like a telephone jack, but the latch is located in one side, making difficult to connect any other cable.


That is not a big problem; filling off the latch from a 6-wires telephone connector (RJ-12) may do the job. Once I was able to connect a telephone cable to the NXT, I started to test the signals. Here is what I found:


lego connector input Holding the connector as the picture shows.


White wire - Appears to be an Analog input, using a variable resistor connected to ground (BLACK) and ~4.5V (GREEN), the NXT measures the voltage coming from this pin. However, some short pulses comes out of this pin; with a capacitor, it stores more than 5 volts


Black wire - Ground. Connected to NEGATIVE.


Red wire - Appears to be grounded. Looks like is connected to NEGATIVE.


Green Wire - There is approximately 4.5 volts coming from this wire. I believe this voltage is used to provide power for the circuit connected at the Analog input (WHITE). If so, I think the maximum voltage at the pin 1 (WHITE) should not reach or exceed 5 Volts.


Yellow wire - I got pulses from this pin. I believe this is used for serial communication together with the Blue wire. If so, this wire must be I2C SCL.


Blue wire - I believe this is the data signal used for I2C port. If so this is the SDA.


Here is the pinout information that I was able to get from the Output ports of the NXT:


connector output signals White wire - Used with the black wire, this pin provides power to the motor. If this line is set as NEGATIVE and the black wire is set as POSITIVE, the motor will rotate in one direction. Set as POSITIVE and the black wire set as NEGATIVE, the motor will reverse. This port is controlled by PWM to set the power level or speed. When the NXT set the motor as brake, it provides low voltage and low current on both signals


Black wire - Explained on the WHITE wire.


Red wire - Grounded wire or NEGATIVE.


Green Wire - There is approximately 4.5 volts coming from this wire. I believe this voltage is used to provide power for the optical sensor that measures the speed and angle when the motor is running.


Yellow wire - Encoder signal 1. Used with the Blue wire, it provides pulses to the NXT to determine the direction and speed of the motor.


Blue wire - Encoder signal 2. It receives pulses from the encoders located in the motor and used with the yellow pin.


Basically, that's all the information that I was able to get from the NXT. I still trying to figure if this information is correct and it may void the warranty or damage the NXT. This information is for educational purposes only.



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