Question

i have a drowning detection system composed of waist belt which includes multiple sensors to detect drowning

what sensors can we use? can you give me sugestions with details please

and can we use heartbeat sensor ? will it be able to detect heartbeats of the swimmer while being inside the belt ?

Answer 1

1.Since the issue is concerned about drowning detection, it is crucial to know the depth to which the victim is drowning using a suitable sensor.The sensor of this category works essentially based on the pressure difference or hydro-static pressure in case of water based application.For this purpose,Water Depth (Level) Sensor which embeds the MS5540C chip can be used.

• About Water level sensor

  • The MS5540C carries a metal protection cap filled with silicone gel for enhanced protection against water and humidity and ensures function of the sensor even when in direct water contact. It can withstand a pressure of 100 m in salt water. But the user should avoid drying of hard materials like for example salt particles on the silicone gel surface. In this case it is better to rinse with clean water afterwards.

  • Features

    • Pressure Linear range (air Applications): 10 to 1100 mbar
    • Under water depth: 10m (can be calibrated with more depth:refer this link for additional details: https://store.futelectronics.com/products/under-water-depth-sensor)
    • Resolution 0.1 mbar (1 cm water)
    • 16 Bit ADC
    • SPI serial interface
    • 1 system clock line (32.768 kHz)
    • Temperature range -40..+85°C
    • Low voltage (2.2 to 3.6V)
    • Low power (Standby current:0.1uA)   
    • Small size 6.2 x 6.4 mm

2.Pulse rate also plays a crucial role to see if a person is in panic, therefore making it easier for early detection of drowning.As such swimming is an activity which is said to decrease the pulse rate by a few readings.So a detailed case study might be required to judge whether the person is in panic or not and what kind of readings we may require if we are going to use a pulse rate monitor.But the problem is that we need to make the sensor waterproof by use of agents like silicon gel.

You can refer this link for better reference since I am not able to explain every detail concerned to my 2nd point

https://www.ecnmag.com/blog/2017/06/ultrasonic-sensors-detect-heart-rate-blood-flow-and-work-underwater

3.Other alternative to the above method is use of FINIS Aquapulse.But I wouldn't suggest it if we have to optimise the cost for this waist belt.

4.As for the last part of the question, a heart beat/pulse rate sensor need to be made water proof if at all they are used underwater. It is infamous that few watches use this kind of technology for underwater pulse detection and have succeeded.So it is completely dependent on how well waterproofing has been achieved while using this sensor.This implies that the microcontroller unit should also be waterproofed

Note:While integrating the water level sensor, choose a depth threshold appropriately to detect drowning.