Respiration is an important parameter in preterm birth children as they are more suseptible to lung problems and apnea. We were toying around with the idea of Impedance Pneumography but then due we read that the electrodes used in impedance pneumography often caused skin irritation in children.

Respiration sensing using a belt seemed like a viable method to sense a child's respiration.
Eeonyx Corparation has some neat textile sensors which works by the principle of Piezoresistivity, The process by which the textile element changes it's resistance depending on whether it's stretched or it is pressed on.
We made an elastic belt using the same material to measure the resistance of the sensor.

The resistance varies from 60k-100k Ohms when stretched, This value is accurately measured using a wheatstone bridge.

Here instead of the strain gauge we have our eeonyx belt.

I had the output voltage measured and plotted and the result was an accurate respiration plot.

A bit of peak detection can enable us to find the respiration rate accurately by measuring the Inter Breath Interval and the breathing frequency. Timers would measure the time diff between consecutive peaks.