How to Calculate the Gain of IC1c Op-Amp in Pulse Rate Monitor Circuit Diagram?

hello

can you help me i don't know how to calculate tahe gain of IC1c the AOP in the diagrame

https://www.eeweb.com/blog/extreme_circuits/pulse-rate-monitor

That one is a little tricky to analyze, but I believe that is a unity gain stage (no voltage gain, but capable of driving additional current to maintain the 1:1 voltage output with a low impedance load).

The opamp will drive the output to maintain 0V between the non-inverting and inverting inputs. While there is a 10K resistor in the feedback path between the output of the push-pull amplifier and the inverting input, at DC there is no current flowing through that resistor so it can be ignored from a gain perspective.

C5 forms part of an RC filter to prevent oscillation with the power output stage and to limit the high frequency response of the amplifier.