Suggestions for filtering the Noise from the circuit output

[Audioguru]

Can you suggest me a way to improve the circuit design to get a AC waveform of the pulse instead of the positive pulse.Can't I use the TIA.
Thanks.

Your circuit senses when blood fills an artery (which blocks the IR light) or not which produces a DC pulse. An ECG circuit measures the AC electrical activity of the heart.

 

[patan.gova]

Yes,the output of the photodiode will be a DC (PPG) signal.
But can you please suggest the things that are to be needed to make the very low amplitude pulse that is obtained with the design shown in the post36 after adjusting the freq to 3.4Hz.
I mean how to 1)make the Pulse signal to be amplified up to the value of 2.5V
2)how to design the effective filters stage needed.
As I am not able to figure the design.
Thanks.

 

[Audioguru]

But can you please suggest the things that are to be needed to make the very low amplitude pulse that is obtained with the design shown in the post36 after adjusting the freq to 3.4Hz.
I mean how to 1)make the Pulse signal to be amplified up to the value of 2.5V
2)how to design the effective filters stage needed.
As I am not able to figure the design.

There is a 'scope photo in post #32. Is that the output? The 'scope is not sensitive enough to show it and the settings on the 'scope are not shown.
Maybe your IR LED is not bright enough. Maybe the gain setting of the transimpedance amplifier is too low. Its gain is increased by increasing the value of its Rf which is only 50k. Try 300k or higher.

The peak voltage is attenuated by overlap from the very simple filters. Second order or third order Sallen-Key Butterworth lowpass and highpass filters are much sharper and will not attenuate the peak levels.

 

[patan.gova]

Yes, the scope photo in post #32 is the output from the design posted in post36.
The IR LED is consuming a current of around 18mA.I changed the gain by using Rf=330K and Rc=15uF making a fc=3.4Hz and the pulse in the output is still not better as shown here **broken link removed** where the the pulses represent the movement of the finger like when the finger is wantedly moved to check the working of photodiode and the other part of output represent the constant placement of finger on the diode.
You said the "peak voltage is attenuated by very simple filter" But can I know where the sallen-key butterworth LP and HP filters should be placed in the circuit.

 

[Audioguru]

Why did you use such a high value capacitor of 15uF that it kills all signals? It cuts frequencies above 0.03Hz!
If Rf is 330k then the capacitor in parallel should be 0.14uF for a cutoff at 3.4Hz but 0.15uF (150nf) is a common nearby value.

If the center horizontal line on your 'scope is 0VDC and it is set for DC input at 200mV per division then the trace is at about +0.75V.
The timebase is 500ms (half a second) per division and nothing happens for 2.5 seconds then a small amplitude 300Hz ripple occurs for 1.5 seconds.
This is not a heartbeat.

A heartbeat caused by blood pumping though a finger placed in between the IR LED and the IR photo-diode would produce one strong vertical pulse every second to two pulses per second.

Why does your scope show nothing for 2.5 seconds?
Then why does it show small 300Hz for 1.5 seconds?

Please replace the capacitor and set the trace on your 'scope so that +0.6VDC is the bottom horizontal line.

Your extremely simple lowpass filter cuts 3.4Hz to an amplitude of 0.707 times the amplitude of very low frequencies. 1.7Hz is reduced to about 0.5.
A second-order Sallen-Key Butterworth lowpass filter also reduces 3.4Hz to 0.707 times but 1.7Hz will be at full amplitude.
The same occurs for a simple highpass and a second-order Sallen-Key Butterworth highpass filter.
Your simple filters overlap and cut the frequencies you want.

 

[patan.gova]

Thanks and
'Why does your scope show nothing for 2.5 seconds?'This interval represents constant placement of finger on the diode to check whether there is any pulse detection.
'Then why does it show small 300Hz for 1.5 seconds?'The pulses in this interval represent the movement of the finger like when the finger is wantedly moved to check the working of photodiode.
I changed the feedback capacitor value to 150nF but there was no detection of pulse and I am confused why it is not giving out any pulse.What do you suggest.

 

[Audioguru]

I don't know why your fixed circuit does not work.

There was a project called HeMon (HEart MONitor) but Google does not show it anymore.
Instead, look at this project: https://embedded-lab.com/blog/?p=1671