Patent ID: 7373192

Claim:
A pulse oximeter comprising: a red drive line for a red light emitting diode (LED); an infrared (IR) drive line for an IR LED; a drive circuit coupled to the red and IR drive lines; a processor configured to control the drive circuit, the processor having a red zero output line and an IR zero output line coupled to the drive circuit, wherein a control signal on zero output lines turns off a red or IR drive transistor providing forward current flow through the red and IR LEDs, respectively, and turns on a sink transistor coupling an anode of the red LED to ground or a sink transistor coupling an anode of the IR LED to ground; and a logic circuit having inputs connected to the red and IR zero drive lines and outputs providing control signals to the drive circuit, wherein the logic circuit is programmed so that the red and IR zero drive lines override other control signals provided to the drive circuit.