looking for a a sensor that will monitor heartbeat

Hello, I just ordered my very first arduino--- one problem i am having is finding a pulse sensor of some kind. I am totally open to creative solutions or relatively inexpensive ones (under $100 or so). I need to buy multiple sensors, so I need to keep the cost done. I read on a a board for Max that someone hooked up a stethoscope to a microphone-- i am open to solutions like these. If anyone can share any thoughts or resources, that would be wonderful! thank you!

I think it is just an electrical thing, my buddy made one years ago in one of his EE classes.

You see them all the time on exercise equipment, where you touch the metal parts and it displays your heartbeat.

ive seen people do it with piezo sensors taped to the wrist. it needs alot of amplification, so be careful with your circuit layout.

If you're not wedded to the idea of doing it acoustically, this is a good page about electrocardiograms.

Love the warning at the top of the page.

Having said all that, a heart rate monitor intended for a treadmill might indeed be relatively cheap on eBay or some such.

It's easy to make a pulse sensor using an LED and an LDR... you fix them somewhere like the finger-tip or earlobe and measure the light passing through, which varies with the blood flow.

There's a circuit I found on the web for this (using a differential amplifier) that I connected up to an analogue input on the arduino. worked pretty well. Mail me if you can't find it and I'll see if I can dig it out.

Alternatively Sparkfun recently started selling receivers that work with the wireless chest-strap type of sensors. Search for "heart" or see http://www.sparkfun.com/commerce/product_info.php?products_id=8661

Here we go, I found the reference… this circuit uses a PIC with 7-segment displays to display heart rate, but I just built the LED/LDR-based sensor part in the bottom left-hand corner of the schematic and connected the signal called “heartbeat” to an input on the arduino instead.

http://web-ee.com/schematics/medical/heartbeat-monitor/

The arrangement of LED and LDR is important - they have to be snug so that external lighting variation is excluded. Also they need to be fixed firmly because any relative movement will give false readings.

Some people recommend making a spring clip to fasten on the earlobe, but I made a small tunnel type thing with the sensors at the bottom, so you slide your finger inside. The LED shines through one side of the end of your finger, and the LDR picks up the variations in brightness on the other side. The brightness varies with the pulse.

I presume Chris O’Shea used a similar technique for this piece he built for the welcome foundation, which I spotted after I’d been playing the above circuit: http://www.flickr.com/photos/pixelsumo/1482453461/in/set-72157602254135243/

Hope this helps!