How to Build a Heart Rate Monitor

Heart rate monitors are useful in determining the condition of the heart in a variety of circumstances. They can tell if an individual is within the parameters of a healthy human or is suffering from poor heart performance. Store-bought heart rate monitors can be expensive, while building one from scratch is a relatively easy process using inexpensive computerized items. When constructing a heart rate monitor, understand that the tools used in the process will be altered from their original condition and as such, will not function any longer as designed.

Things You'll Need

• Lego light sensor
• Soldering tool
• 3 Wires
• White alligator-lead
• Red alligator-lead
• Green alligator-lead
• Serial adapter
• Chest strap
• Small motion sensor
• Mindstorm RCX Lego

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Instructions

• 1

  Remove the brown plate located at the bottom of the Lego light sensor. Minimal force should be needed to pry the plate off. After the bottom is exposed, locate the positive and the ground points. Solder two wires onto each. Locate the signal collector point, located next to the microprocessor. Solder a third wire onto this location.

• 2

  Remove the master light sensor from the Lego piece. Attach the white alligator-lead to the ground wire. Attach the red alligator-lead to the positive wire. Attach the green alligator-lead to the signal wire. Test the circuit to ensure a full loop is being made. Ensure none of the wires are crossed or touching.

• 3

  Connect each alligator-lead to the corresponding wire on the serial adapter. Ensure that the signal alligator-lead is attached to the port on the far left of the serial adapter. The positive alligator-lead should be the next port to the right. The ground alligator-lead should be the second from the right.

• 4

  Plug the serial adapter into the serial port on the small motion sensor. Attach the Lego light sensor into the Mindstorm RCX Lego at the data collection point. Place the motion sensor onto the chest strap and put onto an individual near the heart.

• 5

  Power-on the Mindstorm RCX Lego. As the individual performs physical activity, his heart rate will register with the RCX Lego. Plug the RCX Lego to a computer system to view the results of the subject's heart rate.