NRF905 based on MSP430F149 and wireless design of oxygen means clips (1)

0 introduction

Oxygen saturation can reflect the patient's respiratory function, and to some extent reflects changes of arterial oxygen, in clinical care and home care are of great significance.

Using normal multi-parameter monitoring oxygen saturation, usually with an oxygen means clips fingertip or toe-side to capture optical pulse wave signals, and through a cable signal transmission to the monitoring equipment for processing and calculation. Due to the impact of the cable, patients often inconvenient, but also cable easily fall off, causing errors in measurement, seriously endanger the patient's rescue in a timely manner. Single-module of oxygen saturation measurement device while it is easy to carry, but because of its relatively high power consumption, the use of battery-powered limits the duration of the guardianship: generally these devices can monitor information stored in the device itself, while unable to monitor information sent on time, delayed time rescuing patients. Therefore, this article presents an approach based on RF chip nRF905 and ultra-low power MCU MSP430F149 of oxygen saturation refers to the holder of the design methods, aimed at achieving no cable, long time monitoring and timely sending care information, and other monitoring functions.

1 non-invasive blood oxygen saturation measurement principle

Oximetry (SpO2) is a combination of oxygen in the blood is the oxygenated hemoglobin (HbO2) can be combined with the total capacity of the hemoglobin (Hb) capacity percentage, i.e., the concentration of oxygen in the blood, it is important for respiratory cycle of physiological parameters.

And functional oxygen saturation (SaO2) HbO2 concentration and HbO2 + Hb concentration ratio. Therefore, care is commonly used to estimate the SpO2 SaO2 level. SaO2 theoretical calculation formula is as follows:

The measurement method at Flambeau a bill based on the use of the theorem in the blood of the different components of the absorbance of a red light and infrared rays, respectively, and by measuring the intensity of the transmitted light to calculate values for arterial oxygen saturation.

Its formula is as follows:

Type, △ I'max for infrared communication component of the maximum value of the infrared I'max DC component of maximum, △ Imax to red alternating component of maximum, Imax is red light DC component of the maximum value.

This system is 660 nm red light and infrared 940 nm.

2 system design

Figure 1 shows a block diagram of the overall structure of the system.

This wireless blood oxygen means clips to MSP430F149 micro controller chip for the master, with single-chip i/o interface to drive the LEDs. The system adopts MINDRAY company fingertip SpO2 finger clip that clips of output for the current signal, can be used to reflect light transmission. The current signal after the current one voltage conversion, amplification, filtering, signal conditioning, can be converted to pulse wave signal by MSP430F149 built-in 12-bit ADC sampling into single chip to process, and through the calculated oxygen saturation values, the value is packed by the MCU sends to nRF905 module, and then sent via antenna.

3 non-invasive blood oxygen means clip hardware circuit

3.1 signal acquisition and processing circuit

This system of data acquisition using MINDRAY company ND78108494 fingertip SpO2 finger clips on the clip inside a red light and infrared light-emitting diodes each one, using a reverse connection to connection; in addition there is a photodiode, available to the light intensity into current intensity.