Abstract: A blood pressure measurement instrument controlled by a microprocessor has an inflatable cuff, a pump for inflating the cuff, an acoustic sensor and amplifier for processing auscultatory sounds and supplying signals to a microcomputer, a display for displaying blood pressure, and pressure sensor for measuring air pressure in the cuff and supplying signals to the microprocessor. The invention comprises an improved air bleed rate controller for providing a linearized bleed slope reference signal which is compared to an actual cuff pressure signal from the cuff pressure transducer, to control a variable opening bleed valve. The reference signal is applied at the initiation of the bleed control phase through a logic circuit from the microcomputer and a time delay switch. Additional logic provides a bleed valve override signal for closing the valve during the pumping phase and providing dumping of cuff pressure on the completion of blood pressure measurement.

Abstract: An improved power switch circuit for turning on manually and for turning off either manually or automatically a battery operated electronic instrument. The circuit includes one manual momentary contact on/off switch, a bilateral switch or transmission gate, a microprocessor, and a capacitor that charges to a threshold level when the on/off switch is momentarily closed (on) and that discharges when either the on/off switch is momentarily closed again (off) or after a fixed amount of time has elapsed as determined by the microprocessor. The bilateral switch is switched on when the threshold potential is reached thereby preconditioning the on/off switch for turning the instrument off. The on/off switch can now be closed to discharge the capacitor or the microprocessor can discharge the capacitor thereby switching off the bilateral switch and preconditioning the on/off switch for again turning on the power to the electronic instrument.