I was in search of a technique to develop a respiration sensor based on either LM35 or DS1820/DS18B20.
1) Lm 35 generates analog output with a sensitivity of 0.5 degree centigrade.
2) DS18b20 generated digital output with the same sensitivity.
So my plan is to use an oxygen mask to protect my sensor from ambient surrounding temperature. Now with breath in cold air enters nostrils or passes through the sensor and with every breath out hot air exits from the nostrils.
so one breath cycle takes breath in and out and so there is analogous temperature change and so i want to use ADC pin of ATmega 16/32 to convert the signal variation in the form of digital signal and count the number of cycles every minute or count for 10 seconds and multiply it by 6 to generate breathing rate and finally display it on LCD.
Now thermister mostly available in the market have a thermal time constant of 5 sec or more but i need a sensitivity of atleast 1sec or less to measure high breathing rate.
Normal breathing rate lies in 12-20/min range.
so please help me out in this project and how to interface it with avr