Fit as a fiddle: Sensor measures heart/pulse rate

9th December 2014

Rutronik

Mick Elliott

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Datasheet

Osram Opto Semiconductors’ integrated optical sensor is now on sale a distributor Rutronik. The SFH 7050 for automatic fitness tracking is used in mobile devices, such as smart watches and fitness armbands, and simplifies personal heart rate or pulse rate measurement. The SFH 7050 sensor has three built-in emitters with different wavelengths of 530nm (green), 660nm (red) and 940nm (infrared). Each of them is based on highly efficient thin-film chip technology with narrow spectral bandwidths of around 30nm.

This helps save power and also offers high signal quality for particularly reliable measurements. The red LED has a specified wavelength tolerance of only ±3nm, which guarantees precise measurements.

The emitters enable the pulse at the wrist or fingertip and the oxygen in the blood at the fingertip to be measured. They can be controlled individually so the sensor can be used for different applications. Green light is used for measuring the pulse at the wrist, red or infrared emitters are generally used for measuring the pulse at the finger as they can then also measure the oxygen content of the blood.

The photodiode integrated in the sensor (4.7 x 2.5 x 0.9mm) has an active surface of 1.3 x 1.3mm. Therefore, the diode is very sensitive to light, and enables an extremely compact component to be produced.

It comes with high linearity and excellent signal-to-noise ratio. The infrared LED can also be used in combination with the photodiode as a proximity sensor to start or stop the measurement automatically as soon as the sensor touches or is removed from the skin.

Its integrated optical barrier prevents crosstalk from the three LEDs to the photodiode and therefore corruption of the optical signal or the entire measurement.