Labs Idea #17: Sleep Analysis and Pulse Monitor
Some high-end sleep quality monitors use inflatable mats tucked below the bed lining to measure respiration with an absolute pressure sensor. However, the inflatable mats can be damaged or leak due to normal wear. An alternative solution is the use of a not inflated mat with a highly sensitive pressure sensor.
Sensirion's miniaturized differential pressure sensor SDP3x is a semiconductor MEMS version of the traditional hot wire anemometer. It is easily attached to a not inflated mat in order to accurately measure body movements below the mattress. This includes obviously big movements (e.g. lying down/getting up), but also smaller movements like respiration and even every heartbeat. The mat consists of two ABS sheets (1mm) taped together and the volume in between is filled with volume cloth. (Figure 1).
As opposed to diaphragm based differential pressure sensors, Sensirion's CMOSens® differential pressure sensor characteristic shows high sensitivity especially at low differential pressures (Figure 2). This allows to reliably measure ultra-low differential pressures and therewith accurately measure the flow moving in and out of the mat triggered by body movements.
The measurement of the differential pressure and derived heart rate is presented in Figure 3.
The measurement results demonstrate that Sensirion's SDP3x differential pressure sensor is well suited to measure the heart rate with a sleep tracker placed/located below the bed mattress. The high sensitivity of the SDP3x allows highly accurate flow measurement without the need of an inflated mat. Specifically, the SDP3x integrated into sleep mats allows to measure:
- sleep quality assessment
- heart rate tracking
- breath rate tracking
- activity tracking (e.g. lying down, getting up)
To build a sleep quality monitor the Sensirion differential pressure sensor SDP3x series (Figure 4) can be sourced from distributors listed on the Sensirion website. Communicate with the digital sensor over I2C according to the explanations in the SDP3x series datasheet or use the appropriate evaluation kit.
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