How to decide or select a filter type of an IIR filter

Hello,

can someone explain what should be taken into account to select a particular type to use for the IIR lowpass filter design.

I am confused in the selection of the type to use to design the IIR filter for lowpass implementation if needed fc=4Hz and sampling freq=100Hz for the data attached below.

Thanks.View attachment pulse_data5000.txt

Although you have posted the same data in various previous threads, e.g. https://www.edaboard.com/threads/310607/, your filter specification is still unclear, at least to me.

The pulse waveform has a repetition frequency of about 6 Hz, if I understand right, you want it to be attenuated by the filter. You previously complained about the residual sine passing the filter. As already explained, this is a regular filter behaviour. By making the filter characteristic steeper, the 6 Hz pulse can be almost completely supressed. To fully specify the filter, you need to tell the intended stop band attenuation at 6 Hz.

In addition, you should also specify the passband behaviour. What kind of signals do you want to pass the filter? There might a big misunderstanding because you didn't yet tell the expected filter response, either in frequency or time domain.

Can't you simply sketch the waveform that you want to see at the filter output for the said pulse input signal?

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As an additional remark, you previously said, you expect a "DC line", but this can't be because the input signal is starting from zero, so the output signal must start from zero, too.

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Is it a simple averaging filter problem, e.g. for a PWM DAC? Unfortunately you never mentioned the purpose of the filter.

In this case, the filter specification can be reduced to two or three parameters:
- residual 6 Hz output (stop band attenuation)
- settling time
- possibly permitted overshoot

My apologies for not explain the things clearly.
I am working with the heartbeat measurement from the pulse meter board I have designed. The pulse signals will be in the range of 0.7 to 2.4Hz.The pulse signals are being sampled with ADC at a rate of 100Hz.
The pulse signal sampled with ADC will sometimes contains some frequency components out of this range 0.7 to 2.4Hz(required).My final need is to design a bandpass filter that will allow only freq in range of 0.7 to 2.4Hz.
I want to clear two things
1.switching from FIR to IIR :I already implemented the FIR filter with the microcontroller but then I read that the FIR fitler implementation will have delay but the IIR fitler don’t.So,now I am trying to implement the IIR fitler for which I need fitler coefficients.
2. switching from Lowpass to Bandpass:I was testing how the lowpass filter on microcontroller will work with the matlab fitler coefficients.And It is working fine as the same when implemented with Matlab.
All I finally need is to design an IIR bandpass filter in matlab and the coefficients generated from matlab designed filter will be used for the filter implementation with microcontroller.
I was expecting for a good IIR filter design in Matlab for use the coefficients to make my microcontroller filtering better.
The only requirements I know to design my bandpass fitler are fl=0.7 and fh=2.4Hz ;sampling rate=100Hz and I don’t have idea about the required stop band attenuation, pass band attenuation,passband ripple,stopband ripple or anything else.
So, I need help with bandpass filter design with its needed parameters and its values,its type and order for my requirements.