Reliable and nonrestrictive heart beat detection for physical exercise

A method for heartbeat detection is described that consists of an amplifier and timing circuits connected to three self-adhering electrodes placed on and below the sternum. Connection to the body is achieved by the use of commercial, self-adhering electrodes. These electrodes provided the most consistent and reliable signals and are not affected by movements of the wearer. The signal from the electrodes is amplified using a discrete implementation of an instrumentation amplifier with current limiting at the input to prevent possible electrical shock to the user. The signal is then fed into a filter section with adjustable gain. The filter section provides final filtering of the signal and allows adjustment of the signal level. The output of the filter section is connected to a biasing network which shifts the analog voltage to a level usable by a timing section. The timing section then generates a positive pulse at its output for each detected heart beat