Pressure Sensor

Schematic:

Construction:

  1. This circuit will easily fit on a 1 1/8" square circuit board. It is even easier if you use surface mount resisters. Be sure to position the pressure sensor so that it will fit inside of a block made out of four Lego bricks with the connector sticking out.
  2. Cut of the top and halfway down one side so that when they are side by side the circuit board will sit inside the two blocks.
  3. Cut the side out of two more. On one, drill out two pins in the middle along the side opposite the one you cut out. On the other drill a hole for the connector on the pressure sensor to stick out. Remove all of the inside parts to make room for the pressure sensor.

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  4. Solder a short 3/16-rod to each of the wires that connect to the circuit where it is labeled RCX.
  5. Glue rods into the two holes to replace the pins with super glue or epoxy.
  6. Place the circuit board into its slot and then place the other two bricks on top, with the pressure sensor coming out its hole, and glue everything together.

Implementing:

Plug the sensor into the RCX and set it on light. Use sensor with the Lego Pneumatic system or similar air pressure systems. At low pressure the sensor will read in the 90s and will go down as the pressure increases. This sensor compares the pressure at its input to the surrounding pressure so this sensor can’t be used as an altimeter or barometer unless you placed the sensor in a container to keep the surrounding pressure constant or some other system. But I am not sure if this circuit allows the sensor to be that sensitive.

The sensor:

Motorola makes this sensor. Its full part number is MPX5700GP. There are other versions of this sensor that a differential port. All of these are part of the MPX5700 family so they will work with this circuit.