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Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor
From: |
Tilman Baumann |
Subject: |
Re: [Paparazzi-devel] airspeed_adc with Ardupilot airspeed sensor |
Date: |
Wed, 11 Jul 2012 13:37:17 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 |
On 02/07/12 15:56, Gareth Roberts wrote:
Hi Tilman,
It's the same sensor as the ardupilot classic - it's not great.
http://cache.freescale.com/files/sensors/doc/data_sheet/MPXV7002.pdf?pspll=1
I hooked up the oscilloscope and gave it a test.
The ripple is low, not more than I had on the power supply. Noise seems
fine to me. But I'm not a expert.
The first really weird thing is, that zero is at 2.5V. Negative pressure
is from 2.5 to 0 Volt. (WTF?) And positive windspeed is 2.5 to 5V.
That is bad in two ways. First, for the ADC I would rather have
3.3V[max]. And what is the deal with negative pressure?
And also, there is very little response to actual wind. My relatively
powerful desk fan does not even create a recognizable response. Blowing
at it does, but only very little.
I would guess that you need insane speeds to saturate this sensor.
To increase accuracy I would have to remove that 2.5V offset. Which
would also move me in the range of a 3.3V ADC.
I could hook up a op-amp with one leg on a 2.5V reference. But my wiring
is already insane, don't want to make it worse.
I would have to sacrifice LED to get a usable ADC already. I'm beginning
to really dislike that whole idea...
Damn. The Eagletree sensor was not that much more expensive. And
digital. And calibrated.
Kids, don't try this at home I would say. It's not worth it.