Ear clip pulse monitor - interfacing?

[Michael A. Covington]

Does anybody know the specifications of the standard ear-clip pulse monitor
that is used with exercise machines?

I know in general terms that it contains an LED and a light sensor (CdS?
photodiode?) for a wavelength that is strongly blocked by oxygenated
hemoglobin.

And I know about Jim Thompson's earpulse.pdf circuit, which does a very nice
job of working out the filtering. But did he actually use the type of ear
clip that is used with exercise machines? If so, on the plug, which pin is
which?

 

[Jim Thompson]

On Sat, 13 Nov 2004 13:26:34 -0500, "Michael A. Covington"
<look@www.covingtoninnovations.com.for.address> wrote:

"Jim Thompson" <thegreatone@example.com> wrote in message
news:mvhcp0167mapom8nusltrj0mdu4ktb4e6e@4ax.com...

I did that design in the early '70's, before LEDs were common, so
that's an incandescent lamp (as marked on the schematic) in my design,
but an LED should work fine.

The output is TTL/CMOS-compatible (as also noted on schematic

Pin-out? You got a DVM with an ohms setting ?

Yes, but I don't know if the sensor is a phototransistor or a CdS cell... I
could work it out, of course. I was just wondering. Exercise machines all
seem to use the same ear clip, and I thought the circuit would be out
there...

Somewhere around here in my junk box I have one of those earclips, but
I doubt that today's versions are the same... like I said, it was
around 30 years ago.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Trevor]

On Sat, 13 Nov 2004 22:36:45 GMT, "Nicholas O. Lindan" <see@sig.com>
wrote:

Any old wavelength works. In the v. old days it was a grain-of-wheat
lamp and a phototransistor. I don't remember a CdS cell being used, they
don't like heat and moisture and hermetic packaging is $$, and they are
too big.
If it helps "Modern" oxygenation meters (which also measure pulse)

pass two different light freqencies alternately thru the skin - they
are then able to self calibrate and measure the quantity of oxygenated
haemoglobin.

I can't remember the frequencies involved, but if u want I could dig
out the info when I'm back at work.

 

[Rich Grise]

On Sat, 13 Nov 2004 13:26:34 -0500, Michael A. Covington wrote:

"Jim Thompson" <thegreatone@example.com> wrote in message
news:mvhcp0167mapom8nusltrj0mdu4ktb4e6e@4ax.com...

I did that design in the early '70's, before LEDs were common, so
that's an incandescent lamp (as marked on the schematic) in my design,
but an LED should work fine.

The output is TTL/CMOS-compatible (as also noted on schematic

Pin-out? You got a DVM with an ohms setting ?

Yes, but I don't know if the sensor is a phototransistor or a CdS cell... I
could work it out, of course. I was just wondering. Exercise machines all
seem to use the same ear clip, and I thought the circuit would be out
there...

A photodiode will ohm out drastically different from a CdS. And as others
have mentioned, it'd be quite unlikely that they'd use one of them in
that sort of app anyway.

So you're ohming out two diodes. The one with the greater forward
drop is probably the LED. Then, pick suitable resistors, borrow a
couple of meters, and find out what happens!

Good Luck!
Rich