Hardware Entwicklung zur Messung der Sauerstoffsättigung unter mobilen Bedingungen

Even nowadays continuous monitoring of oxygen saturation, inside as well as outside of medical facilities, especially under mobile conditions can not be performed satisfactorily. Even with small portable finger puls oximeter probes the user is quite restricted in everyday life. A power-saving, mixed signal PCB for mobile pulse oximetry, which is fully integratable into the existing system, is to be developed in this task. An AT91SAM7S works as controll processor on the PCB. The PCB is split in different areas for signal generation, signal measurement, signal processing and data transmission. The sensor signal is amplified and preprocessed in an analog part. After the analog preprocessing the signal is digitalised and put on a carrier signal to be sent to a PC via radio connection for further processing and graphical representation. The PCB is operationable with a single cell lithium polymer battery (3.7 V). Besides self interferences, which appaer as spikes in the H-bridge, the PCB works fine. These self interferences occur due to the quick switchingtime, which is required by the in-ear-sensor used in the existing system. The self interferences were reduced as much as possible, but could not be eliminated completely. The interferences have no influence on the measured signal and can therefore be tolerated to a certain degree. In general the pcb generates a good and well measurable signal, which can be transfered to a PC for further processing. There is a regulation routine implemented in the firmware, which is able to controll the LED current automatically. Also a tissue detection at the sensor is implemented in the firmware.