Demo video here: https://drive.google.com/file/d/0B0yMpI_ZOcoYN2JnSGY2LUp5UUk/view?usp=sharing

As you knock the person off-balance, the heart rate increases rapidly. Once the person is back on his feet, the heart rate returns to a steadier, more relaxed rhythm. The heart rate is represented by a string of LEDs in the shape of a heart mounted on a protoboard. The protoboard is mounted to a servo, which moves in rhythm with the heart beat. The person is carved from a bar of soap, with an accelerometer embedded in its back. 

Process

I first began by individually testing each component’s circuit design and Arduino sketch before combining them.

I started out with the LEDs, testing the circuit in a solderless breadboard before soldering it onto a protoboard. I briefly looked into charlieplexing, before deciding that it was unnecessarily complex for this project. This was surprisingly one of the most time-consuming parts of the project, considering the research I did for the LEDs, charlieplexing, and the careful organization of the components on the protoboard.

The accelerometer was pretty easy to get working, since Adafruit has a library for it, and I have previous experience using accelerometers.

I originally wanted to use a solenoid, since I think the up and down motion of would correspond better to the pulsing of the lights. However, I didn’t want to have to deal with an external power supply or risk ruining my Arduino due to inexperience. However, if I were to give this project a second shot, I would go with the solenoid. I don’t think the servo’s type of motion goes well with the project.

Technical Difficulties

Unfortunately, I couldn’t get both the servo and the LEDs to work simultaneously. I believe it’s an issue with the Arduino sketch, since both functions for the components use the delay function. I chose to keep the LEDs since I think it better communicates my original idea.