Pulse sensor

Harley

Has anyone made use of the Parallax Piezo Film Vibra Tab Mass LTDO sensor? It appears to be rated much higher than my needs, to sense a human pulse., at a 25 lb rating.

Maybe an IR LED/phototransistor combo might work? Anything else? I'd imagine one or more OpAmps would be needed to scale the sensor output to Prop levels for sigma-delta A/D conversion. I'm welcome to all ideas here. An area I've not worked in before. I'm Googling for info on this area too.

Leon

An ADC isn't usually used for heart rate measurement. If you use an IR emitter/detector you can simply amplify the signal, square it up using a Schmitt trigger, and time the pulses.

Harley

Leon said

An ADC isn't usually used for heart rate measurement. If you use an IR emitter/detector you can simply amplify the signal, square it up using a Schmitt trigger, and time the pulses.

Ah, I didn't let you in on my goal. I need the front end to obtain a pulse signal for the display shown. A PTP board and 3.5" LCD to display one's pulse waveform. Yeah, I know I'm doing it the more complex way. Your scheme is OK for normal pulse info, but for someone who has irregular pulse (wife) this engineer would like to 'see' how it is misbehaving.

Using a D/A to simulate a pulse; A/D is seeing raw D/A output without any filtering in this pic.

Duane Degn

Harley, I still have an old blood pressure cuff that attached to a PC to display blood presure and pulse rate. It displayed the pressure over time and you could actually see information about each pulse. (My first heart was always very interesting, no two beats were alike)

You might be able to do something similar with a presure sensor. I agree a piezo film isn't an appropriate sensor here. I've played with a SCP1000 a little myself. I know there an object for it in the OBEX. A BMP085 costs less. I'm not sure which would be best for this application. I wonder how important a cuff is. I can't think of how else (besides a cuff) to monitor the pulse pressure. I'm very interested in what you come up with. I hope you share your results.

Duane

Edit: I think the blood presure device was called DynaPulse.

Duane Degn

Harley, You've seen Rayman's Prop EKG right? I suppose that's the right way to see a pulse.

Duane

Leon

To get that sort of signal you need to use electrodes, which gets you into all sorts of problems, including electrical safety. If you are going to connect it to anyone else, make sure that you have plenty of insurance. I designed something using electrodes once that measured eye position by detecting the signals from the ocular muscles; I used a couple of very expensive medical isolation amplifiers and a medically-approved isolated power supply.

Harley

@ Duane, thanks to that info; no I'd not seen it. Don't know why I hadn't been at Rayman's site and see his approach.

@Leon, I wasn't thinking of contacts, but just maybe a pressure or IR detector scheme. I don't know enough about the quality of the signal if it weren't contact-connected.

Somewhere years ago I recall an IR approach, with IR LED at an angle to the IR photo-transistor as pickup; two holes drilled about 60° angle in a block of metal/wood/plastic, with the LED and photo-transistor fit in the holes. The variations in the vein just under the wrist skin supposedly produced a signal. And I don't even recall if it were displayed or just squared up and measured 1/t for beats per minute. A really slow signal compared to the Prop's 80 MHz clock. When I heard of 3.5" color LCD Rayman had for sale, that began my design on the display end first. Now for the front, sensor portion.