The simplest cardiograph on the Arduino

Hi Habr, now we will measure the pulse.

Having rummaged in Google, it is possible to find the most widespread and simple way to measure pulse - photo plethysmography. Highlight the capillaries under the skin with infrared radiation. Blood passes through the capillaries in jerks, synchronously with the heartbeat. At the same time, the amount of reflected infrared radiation that we receive by the phototransistor changes. In place of the highlight and reflection can be used to see through through (earlobes or fingers). You can even find several options for schemes, such as this one . However, all of them use operational amplifiers, and they are not at hand. But on hand was the Arduino Due board, which has an accuracy of 12 bits ADC versus 10 others.
The method of scientific selection was collected unpretentious scheme:

As the sensor used what was - assembly TCRT5000 . To do without amplification, we had to quite aggressively adjust the working point of the phototransistor. Immediately I make a reservation that on a regular Arduino without additional amplification may not take off due to the lower sensitivity of the ADC. The scheme was brazed on a breadboard, on which a cold-receiver was molded from cold welding (not replaceable in everyday life).
Also in the bins there was a display ILI9341 (TFT01-22SP). It is designed for a logic level of 3.3 V, as is the Arduino Due, so no additional coordination was required. Pinout:

SCK - D8
SDI (MOSI) - D9
D / C - D10
RST - D11
CS —D12
VCC - 5v
GND - GND
LED - 3.3v

A convenient UTFT library was used to communicate with the display .
Next, a small program with the simplest filtering of digital data stream link to the project
Well, actually what came out of all of the above (in the middle of the video, the Arduino did not hang, just rebooted for the demonstration):