How to detect air flow

I’m looking for either a ready-made sensor to do this or ideas how to roll my own way to detect air flow.

I want to detect air flow from a heating vent in a home. I understand I could technically connect to the furnace’s fan but that’s not really an option. I need a non-intrusive way to do this.

When the thermostat signals the furnace “hey, it’s too cold in here”, the furnace fires up and after a short delay the fan kicks in and blows warm air. It’s the moment (+/- a few seconds) when the air starts moving in the room I want this sensor to send a signal to my Panda II.

I don’t need to know how much air is flowing, only that air IS flowing. Parallax has a motion sensor that when triggered sends a high signal to the micro-controller. I’m looking for something similar except for air flow.

Can you make one with couple wires and a peice of paper for wind detection? Maybe :slight_smile:

Look for an Anemometer sensor.

You could also use a temperature sensor and detect the flow of hot/cold air.

How about a piece of very light aluminum foil and two wires? Connect foil to one wire and set the other wire in such a position that it will come in contact with foil when the air flows.

Depending on the flow rate you could also use a muffin fan. Attach a small rare earth magnet to one of the blades and use a Hall effect sensor to detect motion. Some of the smaller brushless fans will turn with very little airflow.

How about a thin piece of aluminum foil connected to 3V3 (and resistor) that blows into a wire connected to an input pin?

Check the Omron and Honeywell sites for ‘air flow sensors’


These may help but they are not cheap (expect ~$50 - $100)

You could use a barometric pressure sensor since the airflow should cause a higher local air pressure.

Air flow sensors typically come in three flavors:

Positive displacement - Air moves some physical object, you measure the displacement of the object.

Pressure differential - Air flows though a tube that is slightly conical with a pressure sensor at each end. The presser differential is proportional to the airflow.

Heated element - Air flows past a heated element. The greater the airflow the more the element is cooled, thus the temperature of the element is proportional to airflow.[/ol]

The first on the list, positive displacement, is probably the easiest to construct at home. The first two ideas that come to mind are using a flexible resistor attached to a piece of paper. When the air flows against the paper it will bend, and you can measure the change in resistance. You could do the same thing with a pot as well. The airflow would cause the shaft to rotate.

If you haven’t found a solution yet, it could also be done acoustically. A small mic or speaker used as a mic with a stage or two of amplification would generate a signal that could be detected on the A/D input. The signal could be enhanced by directly mounting on the heating grate and/or using a small tube to cause an acoustic resonance.