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numeric filter

MOEZ SIWA
Prodigy 30 points
Other Parts Discussed in Thread: MSP430F2003

hello ,

I would like to extract ( or filter ) a signal which  its frequency 216Hz and its amplitude 1.15volt  from another signal 

which frequency is 50 hz and its amplitude 220 volt. I would like to know if I use a microcontroller ADC +MSP430 with DAC or aADC+ DSP+DAC  ?

If there a demo board texas that permit to do this application and visualise the signal 216 Hz please give me its number part ?

thank you in advance .

 

  • Guru 227245 points

    All internal ADCs  of any MSP device (with an ADC, that is) are fast enough to sample an analog signal with the required speed for a 216Hz signal. You can then do an FFT on the sampled values. Any MSP should have enough power to do this, if programmed properly.

    The problem is the difference in amplitude. The MSP cannot stand 220V and if you break down 220V to 2.2V, the 216Hz signal goes down from 1.15V to 11,5mV. So I guess it's better to put a low-pass filter on the original signal, to put an attenuation on the 50Hz/220V while the 216Hz/1.15V remains unaffected. That's not easy, since you need an attenuation of 100:1 on 50Hz, which is 40dB or 20dB/oktave. So you'll need a 3rd order high-pass filter with 200Hz cutoff frequency and you'll end up with the two frequencies in the same magnitude.

    You can do all this in software. I think a 600:1 voltage divider (230V*SQRT(2)/600 = 1.1Vss) combined with an SD16 A/D converter running with 1MHz and OSR1024 will give you 4 times oversampling, and a resolution of 0.02mV for a 216Hz signal of 5,5mVss. The FFT should be able to tell you whether the 216Hz signal is there or not.

    Normally, I'd suggest trying the LaunchPad, but all G series processors for the LaunchPad only have an ADC10/12 and no SD16 converter (someone correct me if I'm wrong). And the MSP430F2003/13 with SD16 have only 128 bytes Ram, which is most likely not enough for an FFT.

    Leaves you to the 4x family devices

    What do you need the DAC for? For visulatization of the 216Hz signal you only need an LED (on/off)

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