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AnalogIn frequency?

Topic last updated 30 Sep 2010, by Daniel Peter. 4 replies
Alex Louden
11 Jun 2010

I'm interested in the frequency of the mbed's analogin - I'd like to read from a few piezo vibration sensors to see if I can determine the position of the source of vibrations

Anyone done anything like this?

Mike Pearce
30 Sep 2010
user avatar Alex Louden wrote:

I'm interested in the frequency of the mbed's analogin - I'd like to read from a few piezo vibration sensors to see if I can determine the position of the source of vibrations

Anyone done anything like this?

Mike Pearce
30 Sep 2010

Hi,

I also wanted to know the max frequncy I can capture so I set up a loop capture and found AnalogIN samples at around 74 us roughly at 14khz. This means of course using rule of thumb (nyquists thumb?) I can capture frequencys of up to 10th of that = 1.4 khz. Thats fast enough for me but it would be nice if it could go faster and gave a double buffer type function. Anyone else done that sort of thing ?

 

Igor Skochinsky
30 Sep 2010

Manual says that in burst mode "The AD converter does repeated conversions at up to 200 kHz". You can make use of it with the driver from Simon Blandford.

Daniel Peter
30 Sep 2010
user avatar Mike Pearce wrote:
nyquists thumb?

Hi Mike

From what I remember, Nyquist's theorem states that you need to sample twice as fast as the bandwidth of the signal you are interested in. So if you can sample at 14 kHz that means capturing frequencies up to 7 kHz. You need to consider using an anti-aliasing filter which is not going to be a brick wall at 7 kHz though, so you lose a little bandwidth there as well.

Regards
Daniel