A battery source of dc voltage continuously energizes digital circuitry for controlling operation of analog signal processing circuitry including a microphone preamplifier, an automatic gain control amplifier, a bandpass section and an output buffer driving audio reproducing equipment. The analog signal processing circuitry is energized on select command from the battery source through a switched on power supply. Automatic operation of the gain control amplifier may be disabled and the bandpass section by-passed in response to other select commands.
An electronic stethoscope including a microphone, amplifying equipment, and a loudspeaker for the user, also comprises an adjustable filter circuit. The filter circuit has a bandpass effect, and the center frequency and bandwidth of the passband can be adjusted at will throughout the audible range by the user.
A combined electronic acoustical stethoscope having a compact conventional appearance is disclosed. The stethoscope includes a head assembly rotatably mounted on a spool and containing at least a diaphragm, a bell, a battery holder, a microphone, a speaker, signal processing means and, a programmable switch integrated with the spool. The microphone, speaker, signal processing means and programmable switch are concealed within the head assembly thereby providing the stethoscope with the compact conventional appearance.
In a local stethoscope unit, acoustic auscultation sounds picked up by the stethoscope chest piece assembly of a local stethoscope unit are converted to analog electrical signals and then converted to digital signals. The digital signals are conveyed to a data communications system, having data communications device and a data communication channel. The digital signals are transmitted over the digital communications system to a remote stethoscope receiving unit. The remote stethoscope unit converts the digital signals back to the original analog signals suitable for listening.
A microphone unit capable of suppressing the sensitivity reduction due to a parasitic capacitance that occurs depending on the structure of an electret capacitor, can be realized by the following manner. Specifically, an output signal (Vout) that is the inverted output of an input signal (Vin) is inputted to an operational amplifier (OP2) that is an inverting amplifier, such that the output signal (Vout) has the same phase as the input signal (Vin) and is amplified. With an output signal (Vfb) of the operational amplifier (OP2) connected to a first electrode of a parasitic capacitor (CX), the parasitic capacitor (CX) functions as a coupling capacitor, while a feedback is applied to an electret capacitor (EC). This allows for an increase in the voltage between both terminals of the electret capacitor (EC), and thus suppresses that the sensitivity of the microphone unit is lowered due to the parasitic capacitor.
In an apparatus adapted to measure a pulse rate of a subject, a plurality of band pass filters, each of which has a center frequency that is different from the others are provided. The band pass filters are connected in parallel to one another so as to be adapted to receive a first signal corresponding to a pulse wave of the subject and be operable to output a plurality of second signals each of which is obtained by filtering the first signal with each center frequency. A first processor is operable to obtain a fundamental frequency of the first signal. A selector is operable to select one of the second signals which is output from one of the band pass filters having such a center frequency that is closest to the fundamental frequency. A second processor is operable to calculate the pulse rate from the selected one of the second signals.
