It's been a while I haven't written anything here, but don't worry, I was working hard.
The electronics part is practically ready, the mechanics part won't be difficult.
The strangely looking thing at the top is plasticine form which will held the optical sensor components such as light to frequency converter and light emitting diodes.
Each time the device is powered it emits light of four colours one after another. It probes the light intensity with exposure time of 10ms, for each color it takes 200 measurements, so it gives approximately 2s per color.
With each measurements it looks for minimum and maximum light intensity values, which will be later used to compute light absorption using Beer-Lambert law (the minimum value will correspond to the moment where the least amount of blood is present in the artery).
The minimum intensity would be incident radiation and maximum would be transmitted radiation.
With each measurements the device adds one line in the text file present on the SD cards.
I am hoping to start gathering the data this week, I will keep you informed with each progress.