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project on heart beat measurement using finger

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moti lal poddar

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Dear sir
my project is to measure heart beat using LM324,IR LED,phototransistor
and microcontroller 89c52.In my project I am facing a problem that i unable to count the pulse by 89c52.I am using 89c52 in counter mode and giving the input through p3.4 the input is the output of the LM324 by placing finger between IR LED and PHOTOTRANSITOR and this output changes their state continuosly high-low-high-low......according to that a LED connected at this position is ON-OFF-ON-OFF.....continuosly but this event is not counted by 89c52 properly for 15 second (actually i want to count for 15 second afterthat multiply the count by 4 to get the total count in one minute) but 89c52 is not counting properly please help me in this regard
 

bluehole

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Check if the Output is in the range of 89c52?

If it is bellow the limit or above the limit it will not be detected.
So can you please measure the OFF state voltage and ON state voltage at the output of 741?
and also check the oscilator frequency.
Make a pulse generator using 555 and check if you are able to count the pulses. If you do then adjust the pulse height of 741 output hence you can count.

Hope it helps.
 

samson A.

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ARE YOU POWERING LM324 FROM 5V. THE OUTPUT WILL NOT GO ABOVE ABOUT 3.5 ON no load. AND with the led connected, it is lower. i hope you have a schmit trigger in the circuit because if the pulse is detected, a single heartbeat can cause 1001 TRANSITION AT THE OUTPUT. UPLOAD YOUR CIRCUIT.
 

moti lal poddar

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Dear sir
my project is to measure heart beat using LM324,IR LED,phototransistor
and microcontroller 89c52.In my project I am facing a problem that i unable to count the pulse by 89c52.I am using 89c52 in counter mode and giving the input through p3.4 the input is the output of the LM324 by placing finger between IR LED and PHOTOTRANSITOR and this output changes their state continuosly high-low-high-low......according to that a LED connected at this position is ON-OFF-ON-OFF.....continuosly but this event is not counted by 89c52 properly for 15 second (actually i want to count for 15 second afterthat multiply the count by 4 to get the total count in one minute) but 89c52 is not counting properly please help me in this regard

i have succcessfully done this project using a not gate at the output of the opamp afterthat i use 2:1 mux for selecting high and ground this perfect ground solve the problem i am facing...........
thanks you...........
 

BradtheRad

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Thinking about how I might detect the smallest change in my finger as blood pumps through it...

I can only suppose that the phototransistor is showing only the slightest change when the heart beats.

The signal is probably low frequency AC at microvolts riding a DC component of a couple volts.

Question: Are you amplifying ONLY the AC part of the signal? All DC component filtered out?

Probably 1,000,000x amplification isn't too much. One op amp gives you 1,000x.

You need an oscilloscope to make sure there's enough voltage swing coming from the op amp to generate pulse transitions that can be counted.
 

mtwieg

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Thinking about how I might detect the smallest change in my finger as blood pumps through it...

I can only suppose that the phototransistor is showing only the slightest change when the heart beats.
Actually if done right, IR pulse oximeters are pretty sensitive, and SNR shouldn't be a problem (for detecting pulse anyways, oxygen is more difficult). If biased properly, the photodiode should give millivolts of signal, at least.
 

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