Heart Rate Monitor
John Beale Dec. 2010 bealecorner.com
is a battery-powered heartrate monitor project I did back in April
1992. Below are a few photos of my log book. It used a three-lead
connection to get an electrocardiac signal (EKG) and then detected the
QRS peak to send out a short range FM-band radio signal, once for each
heartbeat. A separate microcontroller connected to a FM radio
logged the signal. The main challenge was preventing the RF
output signal from interfering with the high gain instrumentation op
amp reading the low level (millivolt) EKG signal. I used separate
shielding and RF chokes to make it work.
In the circuit as
built, I included an audio tone generator around 1 kHz to
modulate the RF signal, and had a toneburst detector on the FM receiver
to detect the signal. You can see that circuit (through epoxy
encapsulation) next to the RF transmitter circuit in the photo of the
completed device. Not shown are the body leads, three electrodes
connected to a stereo miniplug going into the "op amp" section.
to measurements page.