Post by thread:[EE] Heart Beat Monitor

I wonder I anyone can help me. Im trying to receive the signal radiated from a standard cardio breast belt. A far as I could check with my scope it produces a 5 Khz sinusoidal train lasting 7 miliseconds for each heartbeat. The receiver, inside the wrist watch, succesfully receives the pulse even when it is a far as 120 cm. from the transmitter. Nonetheless the signal radiated energy at that wavelength must be very low. What kind of front end do they use in the receiver, considering any antenna inside the watch should be ridiculously small at that frecuency. I suspect theyre using some kind of magnetic loop antenna... Any ideas will be welcomed. Thanks in advance. Bill Mendive

On July 16, 2005 10:26 am, Guillermo P. Garcia Mendive wrote: > I wonder I anyone can help me. Im trying to receive the signal > radiated from a standard cardio breast belt. A far as I could check > with my scope it produces a 5 Khz sinusoidal train lasting 7 > miliseconds for each heartbeat. The receiver, inside the wrist watch, > succesfully receives the pulse even when it is a far as 120 cm. from > the transmitter. Nonetheless the signal radiated energy at that > wavelength must be very low. What kind of front end do they use in > the receiver, considering any antenna inside the watch should be > ridiculously small at that frecuency. I suspect theyre using some > kind of magnetic loop antenna... Any ideas will be welcomed. Just an idea, but perhaps they use the piezo-electric beeper as a piezo-electric microphone. You might want to try a microphone with a 5khz bandpass filter behind it going into a 741 type of amplifier and see if you get something.

Guillermo P. Garcia Mendive wrote: >I wonder I anyone can help me. Im trying to receive the signal radiated from a standard >cardio breast belt. A far as I could check with my scope it produces a 5 Khz sinusoidal >train lasting 7 miliseconds for each heartbeat. The receiver, inside the wrist watch, >succesfully receives the pulse even when it is a far as 120 cm. from the transmitter. >Nonetheless the signal radiated energy at that wavelength must be very low. What kind of >front end do they use in the receiver, considering any antenna inside the watch should be >ridiculously small at that frecuency. I suspect theyre using some kind of magnetic loop >antenna... Any ideas will be welcomed. > > Yes the largest coil, used for loudspeaker filters, you can find at Farnell, works perfect. (Although not so small as the watch ;-) you can easily reach 4 .. 5 meters Stef Mientki > >Thanks in advance. >Bill Mendive > >

Wonder part the person's body plays in being a transmit/recovering antenna. As a test, I volunteer Pookie to wear the belt and you can check the range with her much less body mass/surface area. Can the scope pick up the signal with a simple piece of wire? Bill {Original Message removed}