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Member Since: August 18, 2009

Country: United States

  • Hello,
    I have quite a bit of experience with a sensor called the MPXH6250AC6U http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MPXH6250AC6U-ND
    This little sensor is extremely accurate and is designed for automobile MAP sensor applications. It comes in a 8SSOP package that is easily hand solderable. The sensor is absolute, which means that the bottom end of the scale is complete vacuum and the top end of the scale is about 36PSI (absolute). Keeping in mind that atmospheric pressure is actually about 14.7PSI, the sensor reads about 1.6v at atmospheric pressures. They are also very cheap (about $10).
    From my experience with them, I have found that we have a better ability to create vacuum than pressure, so you will likely not see huge upward voltage swings. I would recommend using 10 bit ADCs to achieve enough resolution for smooth operation as you will not be using a lot of the scale of the device.
    Using a sensor vs. switch opens up a range of possibilities including speed control by amount of pressure/vacuum.
    Another requirement is clean air supply, so look into getting a small inline filter so not to take in saliva.
    A neat idea that you could achieve with a couple pots and some transistors would be making an adjustable switch that has high and low set points. I have found that once I got into microcontrollers, I would spend half a day trying to program what I could have built with discreets in 10 minutes.
    If you have any questions, feel free to email me at alex@campbelperformance.com.

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