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Subject:Re: Electronic circuits
From:Email address hidden
Date:Sat Jan 27 20:37:48 2001
On Sat, 27 Jan 2001 18:50:10 -0500, "Ross Carlisle"
wrote:

>For airspeed you will need a guage pressure sensor. An 8 bit ADC should
>suffice to convert the voltage output of the sensor to digital so you can
>deal with it in a microcontroller...That is providing the ADC range is the
>same as the sensor. If not youll need an ADC with more resolution which
>can get expensive. Ive used a 16 bit ADC from Maxim that works well but
>goes for $60. If you can get the ranges on the ADC and the sensor to match
>(usually by using an op amp setup) then an 8 bit ADC would give you a range
>of 255MPH in 1 MPH increments.
>
Or 0-127.5 in 1/2 mph increments

>For altimeter you need an absolute pressure sensor. I like the Motorola
>MPX4115A. It has a 0 - 5V range which makes interfacing to microcontrollers
>real easy. The most difficult aspect of the altimeter is the software. The
>barometric pressure to altitude ratio is not linear, so you have to deal
>with that in software. The following formula calculates altitude...
>
>Altitude = (10^(log(p/p_0)/5.2558797)-1)/-6.8755856*10^-6
>
>P_0 is the pressure at sea level (0 feet) and P is the pressure at an
>unknown altitude. P and P_0 can be expressed in any unit because they are
>calculated as a ratio.
There are logarithmic output pressure sensors available, IIRC.
>


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