Remember how you tried endlessly to blow off the last candle on your birthday cake? I do. And it was a daunting task with everyone around me waiting for the candle to blow off and finally eat the cake.
This design idea lets you measure the intensity of your blow.
The design is simple, connect the thermistor and supporting resistors and make the micro controller read analog values. The magic lies in the algorithm used in the code. It is the one of the best I have written so far and the maybe the fastest algorithm(in terms of time spent to think) I have written, less than an hour with the client over my head.
R1 is used to heat the thermistor TR1. Resistor R2 and the thermistor TR1 form a resistor divider network used to monitor the temperature variations. Typical values of resistors are, R1 = 47 ohms, R2 = 100 ohms. When air blows over the thermistor, it cools the thermistor, increasing the voltage at the junction. The voltage at this junction is monitored continuously by the MCU’s ADC channel.
In my design, I use the thermistor to measure the pressure/force of my blow. So when somebody blows on the sensor, I serially output the intensity of the blow on a scale from 0 to 200 (values less than 20-30 are ignored as they are caused by ambient changes).
Potential applications include use in breath sensor technologies with use of high quality thermistors and regulating air flow in instrumentation applications.
Click here to get a copy of the code. It was written for the Arduino but can be used with any micro controller. The comments make the code self explanatory.
Update: – An application of this blow sensor made by me and my friend Shanjit, is on display at Ambience Mall, Gurgaon, India starting this Saturday, October 22, 2011 in collaboration with Saurabh Arora, Prabhat Saraswat, Rishabh Verma, Intel and Hindustan Times. Blow on the sensor to launch a virtual Diwali rocket on a huge LED screen. If your blow is powerful enough, the rocket would be fired else, keep on trying. It could win you prizes too. Be there to experience it.
Have a safe and cracker free Diwali.