Created: Sep 01, 2014
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An air-motion detector is a device that measures air flow. It measures the amount of air per unit time that flows through a particular device.
Sensing circuit detects either steady or fluctuating air flows. The heart of the circuit is a radio shack piezo buzzer (P/N 273-060) and an MCP6004-E/P quad op-amp. When a current of air hits the piezo element, a small signal is generated and is fed through C1 and R1 to the inverting input of one section of MCP6004-E/P that causes the output to go HIGH. Resistor R3 adjusts sensitivity. The circuit can be made sensitive enough to detect the wave of a hand or the sensitivity can be set so low that blowing on the element hard will produce no output. Resistor R2 is used to adjust the level of the output voltage at pin 1.
The detector circuit can be used in various control applications. For example, an SCR can be used to control 117VAC loads as shown in figure A. Also, an NPN transistor, such as a TIP29, can be used to control loads as shown in figure B.