erroneous bw bandpass output with constant input

[ChrisHul]

filter_def = create_bw_band_pass_filter( 2, 100, 0.1, 10);

for(uint16_t i = 0; i < 1000; i++) {
output = bw_band_pass( filter_def, 1.0);
}

printf( "output: %f\r\n", output);
//-------------------------------------------------------
yields: "output: 1.00000" expected output: 0.00000 since input remains constant

create_bw_high_pass_filter( 2, 100, 0.1) behaves correctly

[adis300]

It's recommended to use 4th order filter, according to the original implementation.

[fleutot]

If order 2 is wrong, it's not only recommended to use 4th order. Doing so is a requirement. There should be a check that the user does not use order 2.

I was looking for a simple bw filter of order 1, but that would make the member n to 0, which does not work either, right?