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I haven't had much experience with LDRs, and was not sure of the different types that will work best in a circuit like that.

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  • \$\begingroup\$ Maybe you can explain how an LDR can measure heartbeat? \$\endgroup\$
    – Andy aka
    Jan 8, 2016 at 14:18
  • \$\begingroup\$ the LDR is the input to an op-amp set up as a comparator, that will go high whenever there's a change in the input signal (AKA when the blood flows in/out of your finger) \$\endgroup\$
    – Mena Labib
    Jan 8, 2016 at 14:19
  • \$\begingroup\$ Do you have luminous or light-emitting blood? I don't (last time I checked) so it wouldn't work for me. \$\endgroup\$
    – Andy aka
    Jan 8, 2016 at 14:21
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    \$\begingroup\$ was the fact that there's a LED not obvious...? \$\endgroup\$
    – Mena Labib
    Jan 8, 2016 at 14:26
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    \$\begingroup\$ Of course I knew there had to be a light source but your (unspecified) light source has much to do with whether an LDR can work or not. Your profile doesn't tell me if you are an idiot so I asked the question AND, if you want an answer try delivering more details. \$\endgroup\$
    – Andy aka
    Jan 8, 2016 at 14:34

2 Answers 2

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LDRs are very slow and not very sensitive. Use a phototransistor, ideally one matched to the wavelength of your light source. As Andy mentioned, to reject interference from ambient lighting, you may want to modulate your light source so you can filter out ambient rubbish.

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  • \$\begingroup\$ LDR corner frequency is typically hundereds of hertz or better. plenty for measuring a heartbeat. \$\endgroup\$ Jan 8, 2016 at 19:06
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You're looking for TCRT1000 opto-electro sensor, which is reflective opto sensor, So you can measure your heartbeat rate. Don't forget to add filters on the output stage

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