The DF Robot Heart Rate Monitor is a thumb-sized sensor that detects the change in blood volume just under the skin and sends either an analogue or digital signal to the connected Kookaberry.
There is a small slide switch which changes the output a square digital wave (the default position) to an analogue wave. The Kookaberry Pulse app has been programmed to use the digital output.
The best place to detect your pulse with this peripheral is against the skin on the inside of the top joint of your longest finger. The sensor has a small strap which can be used to attach the sensor to your finger, but just holding it there with a thumb enables the best position to be quickly located. It takes a short while to settle down to a steady reading – so be patient!
- Input Voltage (Vin): 3.3 – 6V (5V recommended)
- Output Voltage: 0 – Vin (Analog), 0/ Vin (Digital)
- Operating current: <10mA
- Dimension: 28 x 24(mm), 1.102″ x 0.945″(in)
- Interface Type: PH2.0-3P
How does it work?
The science behind optical heart-rate monitors is photoplethysmography (PPG): the measurement of artery volume using light. When light emitted by the monitor enters the skin, most of it is absorbed by body tissues, but some is reflected. The amount of reflected light depends on several factors, one of which is the volume of blood flowing through arteries near the skin’s surface.
Blood in the arteries absorbs light better than the surrounding body tissues so, as arteries contract and swell in response to the pulsating blood pressure, the intensity of the reflected light rises and falls. PPG devices detect this variation in reflected light and use it to estimate heart rate.