Description
*We chose a very high resistance resistor R1, because most
of the light through the finger is absorbed,it is desirable
phototransistor sensitive enough.Resistance can be selected
by experiment to get the best results.
*The most important is to keep the shield stray light into the
phototransistor. For home lighting that is particularly important
because the lights at home mostly based 50HZ or 60HZ
fluctuate, so faint heartbeat will add considerable noise.
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