Hello
I've been doing a project on blood pressure measurement, and I am following some manufacturer's notes, namely Freescale's and Microchip's app notes. I have some doubts in analog signal conditioning, and I've been working all day on this, with no result at all.
I am using MPX2050 pressure sensor, and I am amplifying its output with an in amp, bringing it to acceptable level for the MCU. If I've been able to extract the pulse oscillations using two chained band-pass filters, but both app notes use one two pole high pass filter. I want to try to implement this with OPA277. If you open the Freescale's app note, the filter configuration is shown on the first page. I want to replace the LM324N with OPA277, and I have a dual supply, so that's not a problem at all. The real problem is that I do not understand how this filter works. If someone thinks this is funny, I agree.
I can see that C2 and R3 (I will be grounding R3) are making a basic high pass filter with a cutoff frequency of 0.48 Hz. The circuit is set as non-inverting configuration, so the filter would allow only frequencies above 0.48 Hz, and block dc. Can someone please explain to me what is C1 used for? Is the combination of R1 and C1 going to ground signals above 4.8 Hz?, and thus eliminate them from the feedback path? I really want to understand the concept of "two pole high pass filter", and I want to make it work.
As I said, I've been able to get a good shaped pulse from the pressure sensor, but I think I can do better. If anyone has any other suggestions as to how to filter the signal, I am happy to try them.
Thanks a lot, everybody!
I've been doing a project on blood pressure measurement, and I am following some manufacturer's notes, namely Freescale's and Microchip's app notes. I have some doubts in analog signal conditioning, and I've been working all day on this, with no result at all.
I am using MPX2050 pressure sensor, and I am amplifying its output with an in amp, bringing it to acceptable level for the MCU. If I've been able to extract the pulse oscillations using two chained band-pass filters, but both app notes use one two pole high pass filter. I want to try to implement this with OPA277. If you open the Freescale's app note, the filter configuration is shown on the first page. I want to replace the LM324N with OPA277, and I have a dual supply, so that's not a problem at all. The real problem is that I do not understand how this filter works. If someone thinks this is funny, I agree.
I can see that C2 and R3 (I will be grounding R3) are making a basic high pass filter with a cutoff frequency of 0.48 Hz. The circuit is set as non-inverting configuration, so the filter would allow only frequencies above 0.48 Hz, and block dc. Can someone please explain to me what is C1 used for? Is the combination of R1 and C1 going to ground signals above 4.8 Hz?, and thus eliminate them from the feedback path? I really want to understand the concept of "two pole high pass filter", and I want to make it work.
As I said, I've been able to get a good shaped pulse from the pressure sensor, but I think I can do better. If anyone has any other suggestions as to how to filter the signal, I am happy to try them.
Thanks a lot, everybody!