Description
Overview
This uses bright infrared (IR) LED and a phototransistor to detect the pulse of the finger, a red LED flashes with each pulse.
Pulse monitor works as follows: The LED is the light side of the finger, and phototransistor on the other side of the finger, phototransistor used to obtain the flux emitted, when the blood pressure pulse by the finger when the resistance of the phototransistor will be slightly changed. The project’s schematic circuit as shown, We chose a very high resistance resistor R1, because most of the light through the finger is absorbed, it is desirable that the phototransistor is 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.
Features
- Use IR LED and optical transistor to detect pulsation in fingers
Application
- Synthesized teaching experiment
Specifications
- Working voltage: 5V DC
- On-board RT9161
- Size: 24 x 22 x 8mm
Arduino Test Code
int ledPin=13;
int sensorPin=0;
double alpha=0.75;
int period=20;
double change=0.0;
void setup()
{
pinMode(ledPin,OUTPUT);
}
void loop()
{
static double oldValue=0;
static double oldChange=0;
int rawValue=analogRead(sensorPin);
double value=alpha*oldValue+(1-alpha)*rawValue;
change=value-oldValue;
digitalWrite(ledPin,(change<0.0&&oldChange>0.0));
oldValue=value;
oldChange=change;
delay(period);
}
