Electronic – Using Unidirectional Electret Microphone as Static Pressure Sensor

electretmicrophonepressure

Hi all posted question on reddit but giving it a shot here too, I've been working on a board that requires a pressure sensor to detect when there is a differential air pressure or not. The board needs to be quite small, and more importantly very cheap.

Even some of the cheapest pressure sensors are $5-$10 which is simply too much for the application. They also provide analog output dependent on the value of the differential pressure, whereas I only need it to detect when pressure is above a threshold.

I have seen something similar in e-cigarette/vape pens. They use what looks like a unidirectional (vented) electret mic as a static differential pressure sensor to detect when you are pulling. I was wondering if any of you have a better idea of how this works. From what I know, electret mics can only be used to measure dynamic differential pressure (sound) and will not work for static pressure.

My assumption is that to use the unidirectional mic as a pressure sensor they might instead measure the capacitance of the electret. I'm not sure how well this works considering that the ones I have seen have an internal JFET that wont allow for this measurement

Hoping some of you have some better answers as to how the e-cig companies use them for pressure sensors.

Best Answer

Some of the e-cigs use the sound of the rush of turbulent air flowing past a conventional microphone to trigger the ASIC.

Some use a capacitive pressure sensor in the 10-20pF range that changes about 10%. There are ASICs to detect the capacitance change.