Raymond - Interesting. Any idea what type of microphone is in the iPhone headphone cable?

I'm OK with this being a challenging project. If it was easy, it wouldn't be fun and I wouldn't be on here picking the brains of you smart people

I'm not sure you understand the difficulty of the challenge, but hey, go for it and let us know what you get. Please remember that in the case of that Iphone app, I suspect that they are making use of a lot of hardware in the phone (you know, the kind of hardware that one might fine useful for voice recognition and the like) in addition to the software. What I am trying to point out is that the microphone used with the headphone cable may not be the difficult part.

 

Well I don't see how it could be even accurate with sound. Spirometers measure air volume. That is why I figured all the works where in the device (I did not read the paper). I have seen devices that transfer data to the cell phone via the microphone input. Figured it was the same.

 

I'm not sure you understand the difficulty of the challenge, but hey, go for it and let us know what you get. Please remember that in the case of that Iphone app, I suspect that they are making use of a lot of hardware in the phone (you know, the kind of hardware that one might fine useful for voice recognition and the like) in addition to the software. What I am trying to point out is that the microphone used with the headphone cable may not be the difficult part.

And you can bet there is a whole lot of sound processing going on. I would be highly suspect that the thing even works. My guess is you would need ideal condition to get the thing to work.

There is a similar app for the Android. I gave it a try and haven't even come close to getting it to work.

 

Thanks for all the comments, everyone! This discussion is really helpful.

I have no doubt that the most difficult part of this project will be the audio processing, once I manage to capture the data. I'm sure I'll pick all your brains about the audio processing, too, when the time comes. But for now, my first focus is on trying to just get the data to process (so that I even know what I'm dealing with), which is why I'm so focused on the hardware.

Alec - you mentioned the idea of using a MEMS accelerator...interesting idea -- how would that work?

 

On a related note - Does anyone know of a good microcontroller/processor for doing large amounts of audio processing at relatively low levels of power consumption?

 

On a related note - Does anyone know of a good microcontroller/processor for doing large amounts of audio processing at relatively low levels of power consumption?

Why don't you just use a phone for starters? You get everything right there. Even a really nice display. You might be able to add a micophone and maybe a preamp and filtering to help improve on what is being detected.

 

Good idea re: the phone. I'm not as familiar with Java, which I think is the language you program Android apps with (I have an Android phone). But I guess I could learn it.

I was planning on just writing something in Python, C++, or using Matlab on my laptop to do my prototyping. But a phone would certainly have a closer feel to a wearable.

 

Alec - you mentioned the idea of using a MEMS accelerator..

Actually, an accelerometer . The sort of thing that's used in smartphones and tablets for fitness apps, spirit-level apps (gravity induces acceleration) and so on. It gives output voltages proportional to acceleration in three co-ordinate directions, so the voltages could be processed to detect heartrate.

 

Woops I meant accelerometer...phone auto-correct fail

So do you think each heart beat would cause some kind of motion that's detectable with the accelerometer?

 

So do you think each heart beat would cause some kind of motion that's detectable with the accelerometer?

IF the apps use the accelerometer as the sensor then yes. A bit of googling should confirm if this is the case.

 

Hi,
I do not know whether you built anything, but i have an idea using two mems microphones. Let me know if you are still interested

 

Picking out the heartbeat *acoustically* will be extremely difficult. Since it sounds like direct contact is allowed, consider other technologies. My Polar heart monitor is low cost and transmits the heartbeat by radio to a compatible receiver. Old tech, very reliable.

ak

Hola ak

The point is, how yours detects the heartbeat so it can transmit it?

 

The one I use has a strap that circles the chest, with two conductive pads, one on each side of the heart. Between them is a very small electronics module with an internal battery. That leaves two options,

1. The module is essentially a voltmeter. It measures the voltage difference at the skin surface.
2. The module is essentially an ohmmeter. It injects a *very* small current through the skin and measures the change in voltage, or imposes a very small voltage across the skin and measures the change in current.

Either way, the electronics package now has a signal that varies throughout a heartbeat, just like an EKG. It also varies with changes in contact pressure, which can be large during exercise, so something has to condition, process, and analyze the signal to extract the frequency components that are caused by the heart. At this point it transmits either the raw signal so the receiver can calculate tnd display the value, or it does the processing and transmits only the number. It seems to average things over 10 seconds to get rid of all of the noise components.

Polar has been the industry leader for decades, so there have to be papers and patents on the web that have more details. Here si the current product page:

https://plr.factoryoutletstore.com/...7.html?category_id=69230&catalogitemid=406470

ak