Simple Air flow detector circuit
This circuit can be used to give visual indication of the rate at which the air flows. It can be applied also to indicate whether the air is flowing in a given place.
In this project, i shall be using a filament of an incandescent bulb as my sensing part in the circuit that I shall build. When the air flow shall be zero, the filament resistance will be low and when the air flow is available, the filament resistance will of course drop simply because the air flow will remove the excessive heat that will be generated from the filament. The variation in the resistance will lead to a variation in the voltage across the filament. The said variation will be picked up by the op-amp and the brightness of LED at the output will be varied proportional to the flow of the air.
- Make filament L1 by removing the glass of a brand new incandescent lamp.
-Power the circuit Using the 12V DC battery or power supply
You can design a regulated power supply with LM317, as it provides variable output depending on the value of variable resistor attached at its output pin.
- Make filament L1 by removing the glass of a brand new incandescent lamp.
-Power the circuit Using the 12V DC battery or power supply
You can design a regulated power supply with LM317, as it provides variable output depending on the value of variable resistor attached at its output pin.
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The 7805 is used as a constant current source, it generates a current of about 5 volt divided by the 100//470 resistor (which is 5 volt / 82 Ohm) = 61 mA into the filament. This is quite a lot of current, the R1 Resistor will need to be 0.3 Watt minimum.
This current heats up a filament, which is a resistive wire. The voltage over the wire which is fed by this 61 mA will be changed by how quickly the wire loses its energy (by conduction/radiation/heating up air which flows over it).
The resistive wire has a positive temperature coefficient, when it gets hotter the resistance will increase and subsequently the voltage across the filament will increase.
This voltage is compared to a set point voltage which is set by R4.
If the voltage across the filament rises, then it is not getting much cooling. (no air flow)
If the voltage over the filament it reaches the set value the LED will be switched on.