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In NXT-G, there was a "Legacy" Block pack which had blocks to allow for the use of RCX motors/sensors with the NXT, as long as you had a converter cable. However, the EV3 software does not have this, and it currently does not appear to have support for converter cables due to the lack of special programming blocks you can download.

What I basically need to do is connect two touch sensors to the same port, so that the EV3 brick would get input if either one is pressed. I have a pair each of RCX, NXT and EV3 touch sensors. I also have three of the NXT-RCX converter wires. Unfortunately, none of the sensors are working with the converter cables, and I cannot use this or this method because I'm preparing for a competition which doesn't allow modification of lego parts.

I came across this thread from the lego site from 2013 regarding this issue, but it offers no solution. I've even tried using the raw sensor blocks with the touch sensors, but they don't give me any output.

I am also only allowed to use the EV3-G programming interface.

Does anyone know how I can use these split cables with the EV3 brick?

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Unfortunately, you cannot use the LEGO 8528 (NXT to RCX adapter) cable with sensors on the EV3. You can use it with motors though.

This is because the adapter cable only connects to pins 1 and 2 on the MINDSTORMS (RJ12) connector. On the NXT input (sensor) ports, pin 2 is GND.

NXT input port connector

On the EV3, however, pin 2 on the input port is no longer GND. It is used to tell the difference between NXT sensors and EV3 sensors.

EV3 input port connector

Without a proper ground (GND), the sensors will not work correctly. This is why the videos for modifying the cables use pin 3, which is GND on the EV3.

Furthermore, for those not restricted by the rules of a competition that can make their own cable, you also need to know that the EV3 firmware lacks the ability to send power pulses needed by "active" RCX sensors. From the NXT hardware developer kit:

NXT hardware developer kit: active sensors

So, don't expect the RCX Light sensor or the RCX Rotation sensor to work with the EV3 even if you make your own cable because it lacks this feature.

As a side note, RXC motors will work with the LEGO 8528 cable and the EV3 because pins 1 and 2 on the output ports are for motor + and -. They work exactly the same as Power Functions motors as described here.

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  • Thanks for all this info! I'm going to try and create a custom block now even though I've never tried to do so before. Also, I'm going to check the block for the sound sensor out since that is an analog sensor, and it just might work.
    – undo
    Commented Oct 8, 2016 at 17:27
  • Also, where did you get those diagrams from?
    – undo
    Commented Oct 8, 2016 at 17:37
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    The diagrams are from the EV3 and NXT Hardware Development Kits available on the LEGO MINDSTORMS download page. lego.com/en-us/mindstorms/downloads
    – David Lechner
    Commented Oct 8, 2016 at 18:50
  • Creating your own block won't help. The problem lies with the automatic sensor detection in the firmware. If the sensor is not detected as an analog sensor (Touch, Light or Sound) in the Port View, then you will not be able to read the sensor value no matter which block you use.
    – David Lechner
    Commented Oct 8, 2016 at 18:58

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