Oximeter protocol

Main devices and principle introduction:

MCU, memory (EPROM and RAM, two devices that control LED infrared sensor, filter and enlarge the signal received by photodiode, digitize the received signal to provide microprocessor analog-to-digital converter, small LIQUID crystal display (can support OLED/TFT/ digital tube screen)

Leds and photodiodes are placed in small probes in contact with the patient's fingertip or earlobe. By driving a red light (660nm) and an infrared LED(910nm) in turn, the blue line shows the induction curve of reduced hemoglobin by the receiving tube when hemoglobin does not have oxygen molecules. From the curve, it can be seen that reduced hemoglobin has a strong absorption of red light at 660nm and a weak absorption length at 910nm.

The red line shows the induction curve of hemoglobin oxygenated by the receiving tube of red blood cells with oxygen molecules. The absorption of red light at 660nm is relatively weak, and that of infrared light at 910nm is relatively strong. In blood oxygen measurement, reduced hemoglobin and aerobic hemoglobin are measured by detecting the difference of light absorption of the two kinds of light at different wavelengths, and the measured data difference is the most basic data for measuring blood oxygen saturation.

Tests of blood oxygen at 660 nm and 910 nm wavelength two of the most common, in fact to do higher precision, in addition to two wavelengths increase, even as high as 8 wavelength, the main reason is that in addition to the reduction of hemoglobin and human hemoglobin oxygenated hemoglobin, there will be other hemoglobin, we often see is carbon oxygen hemoglobin, The more wavelengths you have, the better you can do it.

Finger clip oximeter scheme specification parameters

Display format: LED display, OLED display;

Oxygen saturation display: 35-100%, 2-digit, 7-segment digital display;

Blood oxygen measurement accuracy: blood oxygen saturation in 70%-99% is ±2%, less than 70% is undefined, pulse rate is ± 2BPM, blood oxygen alarm range is consistent with display range, step size is set at 1%;

Pulse rate display: 25-250bpm, 3-bit 7-segment digital display;

Pulse wave display: 6 segments bargraph display;

Peak wavelength range of 2500 nm-1000nm;

Battery low voltage indicator: LED symbol;

Power requirements: 2 no.7 1.5V alkaline batteries, voltage adaptation range: 2.6-3.6V;

Power consumption: less than 40 mA;

Resolution: Blood oxygen saturation ±1%, pulse rate ±1bpm;

Measurement performance under weak perfusion: when pulse filling degree is 0.3%, it can correctly display blood oxygen and pulse rate values, data iodate cycle 0.25s~2s;

Resistance to ambient light interference: the deviation of blood oxygen measured under indoor natural light and existing lighting source is less than ±1% compared with that measured under darkroom conditions