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Sensor to sence human heart pulse?

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cubdh23

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I have a project in mind and one of the main things is to pick up the pulse on our wrists. I was just wondering if you had ideas on how to capture this.
I dont know if there is a sensor that can pick up very small pressure like that.
or maybe i need an amplifier to amplify the pressure X1000 and then put it to a comparator for digital reading. Any ideas? would be appreciated.
thanks OR maybe even a small mic. like the mic on a stetescope. You think that would work in capturing only the pulses if it is wrapped around the wrist.
 
Ive seen in hospitals where they have this thing that is clipped on to the finger that has an LED on one side and a sensor on the other. The pumping of the heart i gues makes the blood vessel larger than smaller, so i guess the sensor measures a change in light. doubt it will work on the wrist without a much brighter LED
 
The LED sensor can be used in a reflective mode - instead of the light passing through the finger you measure the light reflected from the body part. The LED based blood volume measurement is called a Photoplethysmograph.
 
he's right im wrong. i was just guessin. so i gues this would work on the wrist seeing as ur veins are real close 2 the skin
 
Googling on pulse oximeter brought up a nice site that explains how the fingertip pulse oximeters work - pretty simple concept actually. A comparison of light at two different wavelengths yeilds an indication of oxygen saturation.

It appears that some of the wrist type blood pressure meters are similar to the traditional arm type (sphygmomanometer) in that air pressure is increased until blood flow stops and the air pressure is then reduced while measurements are taken and interpreted to extract the desired information. With the manual type, listening to the blood start to gush past the restriction imposed by the inflated cuff is compared to the manometer reading. In the electronic type a pressure sensor analyzes the subtle variations in cuff pressure, caused by the arteries pushing back, and interprets the data. As I recall, oscillometric is the word used to describe this method.

A basic heart rate monitor looks at the slight but reliable potentials that can be measured at the skin surface that come from the electrical impulses that tied to the beating of the heart. The common chest strap type pushes two electrodes against the chest to make the measurements. There are other types including the kind I see at my gym where it looks at the electrical potential between your hands. Apparently there's enough information in that to reliably derive heart rate. Ramsey electronics sells an EKG kit for $30 or $40. The instructions describe connecting it to an oscilliscope.

All of the electronic methods described have one thing in common - that some pretty sophisticated processing of the raw data that is gathered, is required. Pressure or voltage levels are extremely low so there is lots of noise or interference.

I mention this stuff so that you might do a little reading to help guide you. I wonder if you couldn't use a sound card and some audio analysis software as a tool.
 
Thank you so much steves.
That was very insightful and helpful. Im going to look into it and see if this thing is doable. thanks a lot. I wanted to develop a very cheap work out motivational device that i can hook up to the computer to keep track of work out intensities. There are some on the market right now but they are rather expensive. Im pretty much just wanting to do this as a hobby. thanks
 
Ever use OpAmps? there's a specific circuit called an "Instrumentation Amplifier" which comes on it's own IC now, these can easily be used in EKG's (the heart monitors you see at the hospital)...

An instrumentation amp has two inputs, one you get from say... your hand... the other from your chest... this is a super sensitive amplifier that will pick up the very very tiny voltage potentials caused by your heart and amplify it to something useable.

Google "Instrumentational Amplifier" or something like that. It uses three OpAmps, but as i already said, you can get them in there own IC package now.
 
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