Testing time!

Its been a bit of a scary week in all honest in regard to this project. Plenty of realisations, compromise but in hand with this came a lot of learning.

I noticed my pulse sensor was working a bit oddly when max reported values of only 50, 54, 60, 66, 75, and 85 (some more onwards) seemingly the gaps were becoming further apart. I tried power supplys etc, trying to change almost every component, the arduino itself got replaced etc etc. No luck.

After a LOT of research and a lot of thinking i starting looking at other options including the Polar Heart Rate Monitor Interface (HRMI) board by Dan Julio. I got in contact with him and we talked about how the HRMI transmits data through ASCII code to other programming environments. We talked about other solutions to getting a stable heart rate into an Arduino and he also mentioned an inductance device that also picks up the the transmissions for a Polar strap sensor and outputs as a clean 3V signal.

He went on to mention how serial connections between the Arduino and environments (such as PD and MAX) experience lag and bad averaging. This seems to be what is happening here. Because of lag times the board cannot physically sample many more then around 10 samples per second. This makes sense as at 60bpm i was experiencing 10 different values but at 85bpm only around 8. Unfortunately the higher the heart rate, the higher the error which of course makes things difficult.

SO...

I am going to get a HRMI and try and get it working serially at first then attempt to interface it with Max/MSP via either logic level serial or I2C protocol. If Max will not accept such messages then i will have to make do with some averaging functions and use the work i already have. If this is the case i don't see a huge problem as the heart beat will still meander around 60-75 bpm until electricution events where it will jump up very quickly. The issue may be that the reported values at the higher heart rates will jump quite erratically between 90-120bpm. If this is the case i may change the way i report the visual, particually in regard to colour, where it works on a three tear scale, blue for resting (50-65bpm), yellow for active (70-85bpm), and red for stimulated (90-120bpm)

So im going to have a bit of a think i reckon before spending £50 on the HRMI and £15 on the polar strap. Up side is the devices will be much more stable in terms of reporting the heart rate (no need to signal condition etc like i'm having to do at the moment), and it is better attached to the performer. The current finger attached device has a tendency to react badly to lighting level changes.