I'm making a heart beat sensor that will be outputted to an arduino that is displayed on an LCD screen.

I have attached a circuit, i tried making this but i understand this will just amplify a analogue input however i would like the analogue input to be converted to a digital output.

i'm thinking about using a op amp to compare the voltage of the IR detector to the supply voltage and placing my finger over the IR emitter for a heartbeat.

Has anyone got any suggestions?
Thank you

 

An op amp could be configured to do what you want. Specifically, a comparator is a type of op amp that's optimized for this kind of application.

That said, if you have an analog input available on your Arduino, you could just read the analog voltage on that pin and let the code set the threshold voltage.

Playing devil's advocate against myself now... If you have a long wiring run between sensor circuit and Arduino, a digital signal might be safer than an analog one, or at least easier to design in a reliable way. Also, depending on your Arduino code plans, you might want digital input so that you could use hardware interrupts.

Without knowing exactly what you need to do in the Arduino realm, my gut feeling would say just use the analog input and be done with it.

 

I think the circuit should more or less put out a square-ish signal at the emitter now. If you set the I/O pin to an edge interrupt......that interrupt rate should match the pulse rate.