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Errors in "Heartbeat Measurement Circuit"

There are so many typo errors in the activity "Heartbeat Measurement Circuit" that it becomes confusing to read.

For instance Amplifier Circuit (C1, A1, R3), should be (C1, A1, R1).

First order low pass filter (A2, R4,C2), should be (A2, R2, C2).

Throughout the rest of the article, the resistor numbers are totally wrong.

At the final amplifier, there is no R6.

On the hardware set up picture, the OpAmp is wrong !  It should be OP484, but shows OP482.

I notice naming typos in many of the activities, but this is the first one with so many that it becomes very confusing.

  • Hi Enginee_2021, thanks for pointing this out. It looks like the reference designators weren't transcribed properly from the original ADALM1000 based exercise: I've updated the schematic on the ADALM2000 version, adding in the IR LED circuit and replacing the voltage source with a current source / resistor, which should more closely model the actual circuit.

    Also the OP484 discrepancy was noted, but it mentioned that the schematic used OP184, which isn't correct. It's the OP284 that is included with LTspice - they can be used interchangeably. This is pretty typical - if there's single/dual/quad op-amps/comparators, there will often only be one model.

    Let us know if you see anything else amiss.


  • Hi Mark,

    Thanks for the update.

    I really liked this project and would like to expand on it by having a circuit element determine the frequency and display it on a three digit seven segment display.  How can I go about learning how to do this ?



  • HI:

    The simplest way to extend a project like you describe would be to make use of a single board computer or micro-controller such as an Arduino. There are probably even example Arduino scripts on the web that measure an analog signal (such as the heartbeat waveform this circuit generates) , extract its frequency / period and display it on either an LED or LCD display.