Optical Sleep Sensor Platform

Besides piezo based bed sensors 2M created also optical sleep sensor solutions. The principle relies on an optical fiber that is placed under a mattress using a principle which is called microbending. 

From 2016-2018 2M, Kempenhaeghe and TUe focused on creating new monitoring solutions for medical applications around epilepsy, sleep apnea, parkinson and sleep related disorders. Within the first Bedsense project an optical sensor solution was used. 

At the moment this system is still available as reference system. 

Optical Sleep Sensor System components

The optical sleep sensor system exists of the following components:

Optical sleep sensor raw datalogger

  • Functions:
    • Store measurements of upto 3 sensors in raw format for later signal analysis
    • Live data-feed in Matlab for real-time testing of features (via USB interface)

1-3 Sensor strips

Accessories

  • Power supply (5V)
  • Micro SD card + adapter card
  • External sync: TTL, 3.5mm jack cable
  • Remote control: start/stop recordings and check recording status when the BedSense system is placed under a hospital bed.
EU EFRO

This project was made possible by a contribution from the European Regional Development Fund as part of OP-Zuid. For more information see EFRO.

contactless bed sensor - datalogger

Technical specifications

Sensing

  • Sensors: 1 to 3 sensors
  • Sampling Rate: 100 Hz
  • Sampling Rate Drift: 0.021% / ºC
  • ADC Resolution: 24 bit (20bit effective)

External synchronization

  • Sync Pulse: K x 0.5 seconds with K=1-144
  • Sync Amplitude: 0 volt (off) – 3 volt (on)
  • Sync Frequency: 10 minutes (first pulse; K=1 at t=0 sec)
  • Sync Interface: 3.5mm mono jack plug

Power: 5V power adapter and internal battery powered (upto 10 hours)

Recordings: max 100 files

Storage: 32Gb micro SD card

BedSense -Minimal Intrusive Sleep Monitoring Solutions
Optical fiber technology

Data output

Stored data files can be exported to BDF format with the supplied BDF convertor. BDF is the 24-bits version of the EDF file. BDF files can be viewed with multiple (open source) software packages like EDFBrowser. The BDF file contains 3 data signals per each connected sensor channel XX:

  1. ChXX: 24 bit sensor data
  2. ChXX_Syncpulse: Sensor synchronization pulses
  3. ChXX_Temperature: Sensor temperature (updated every 0.5sec)

So when all 3 sensors were connected, the BDF file holds 9 signals in total.

contactless bed sensor

Measurement results

122 complete night recordings have been made at Kempenhaeghe which are analyzed and used for creation of new algorithms. BedSense is available as a high-end research evaluation prototype for detailed monitoring of people and patients. 

BedSense - Breathing rate, heart rate
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