Breakthrough!

Having listened to my heart signal by pressing the piezo contact mic up to my chest, I heard a clean signal whenever I was motionless, but it became substantially noisier whenever I ran in place. Attempts to filter this noise out and isolate the pulse (with high and low pass filters, an FFT filter and an equalizer) were not achieving much. Even when it was taped over my heart and held fast by the chest strap, the large vibrations of my feet impacting the ground and the shuffling of the unit against my body were too loud and the sound of my heart beating was spread across the same frequencies.

About ready to conclude that I would have to give up on the piezo mic and instead perform surgery on my polar chest strap with an exacto-knife to try and find a place where I could solder on wires to interface it with the forthcoming Arduino chip, I suddenly heard a metronome-like chirping sound.

I had moved the contact mic from directly over my heart to the middle of my breast bone; it was now touching the center of the polar transmitter. I held my breath and the click rate subsided, then I lifted one of the rubberized electrodes off of my skin and the clicking stopped. To my immense surprise, the polar T31 was giving off an audible signal to the piezo mic!

What a relief! I could now use the polar chest strap I’d bought off of craigslist as it was meant to be used and I could also use the piezo mic I’d made, which would be much easier to figure out how connect to the Arduino.

The chirp the T31 makes every time my heart beats occupies a much narrower and more distinctive frequency distribution than the direct sound of my heartbeat, so filtering the signal became a much simpler task.

Here is the recording of the piezo mic pressed on the T31 transmitter as I stand, run in place, then stop:

Here is the spectrum analysis of that recording, showing a high spike at 5100 Hz:

I equalize the audio over this same range:

This is the well-filtered result:

The spectrum analysis of the equalized signal:

Updates on other progress:

Location: Having not yet received a reply to the email I sent on Wednesday to the departmental administrator of the Physics Astronomy building, I have not yet been able to scout the planetarium to see if it would be an appropriate space, although I am very attracted by the idea of it and have thought about a modification of my floor plan for a circular room. Here is a preliminary test sketch:

I scouted Raitt 116 and 121 last week and they would both be practical options, albeit not particularly desirable ones. 116 is an 18’ X 26’ rectangle with a 10’ ceiling, 4 windows on one wall a tile floor and all movable furniture. 121 is larger, at 35’ X 26’, with an 11’ ceiling, a wider wall of windows. Its floor is stepped and carpeted. Honestly, I am undecided about whether this additional obstacle could add to Follow Your Heart!, but I think it would more likely detract. There is a larger size projector already in 121 however, and I would need to see if I could angle it from the booth it sits in, toward a mirror on the ceiling.

Microelectronics: Having placed my order on the 16^th, the Arduino BT will hopefully be arriving early next week. I purchased an accelerometer from Sparkfun today, so it may arrive a little after the Arduino. As described in my concept architecture, I plan to use heart rate as my primary system for triggering phase two of the light’s behavior. However, should I prove capable of using the accelerometer as a reliable means of locating the participant’s position relative to the light, I will use the change of heart rate just as supplemental data for the program.

Programming: Having downloaded Processing on Thursday night, I have begun to work from its examples and tutorials to write my program. Here is a screenshot of something I made Friday morning which has the isometric lattice structure I plan to use: