Design and implementation of human skin measuring instrument based on DSP[图]

The skin is one of the most important organs of the human body. It has many functions. First, the skin separates the outside and internal organs and acts as the body's first barrier. The skin blocks the invasion of external bacteria, dust, etc. through the thick cuticle, ensuring a safe environment in the human body. Second, the skin is still an important secretory and excretory tissue. There are a lot of sweat glands in the skin, sweat secretion and sebum excretion through the sweat glands. The skin also has a thermoregulatory effect. It can be said that the skin is inextricably linked to the health of the human body. The medical community has discovered that the health of the human body can be understood by examining some physiological indicators of the skin. Accurately grasping the changes of human functions through the detection of skin physiological parameters is a major problem facing the medical community today.

This paper introduces a design scheme of a human skin measuring instrument based on DSP.

1 overall design

The entire measurement system consists of temperature acquisition, humidity acquisition, pH acquisition, I2C bus, DSP, Flash, USB interface and applications in the PC. The overall block diagram of the system is shown in Figure 1.

The working principle of the whole measurement system: the advanced human skin sensor is used to separately collect the temperature, humidity and pH of the human skin. After the corresponding controller process, the data is sent to the DSP through the I2C bus for filtering and processing. The data is then sent to the application in the PC through the USB port, and the data is processed, displayed, and graphed in the application to determine the health of the human body.

2 hardware system design

2.1 Communication between TMS320VC5402 and indicator acquisition module

In the system design, TMS320VC5402 is used as the main controller, and each indicator acquisition part communicates through the I2C bus. The I2C bus is a bus system developed by Philips. It completes the conversion of 8-bit parallel port to I2C bus protocol, so that some controllers without I2C interface can directly connect to the I2C bus for communication. In the system, the TMS320VC5402 is set to the master mode, and each indicator acquisition part is set to the slave mode. In this way, it is convenient to add other indicator acquisition modules, which can be directly "hanged" on the I2C bus, as shown in Figure 2.

2.2 Humidity Acquisition Module

Consider the special requirements for measuring human skin. The measuring instrument adopts a polymer membrane humidity sensitive capacitance sensor. The polymer membrane humidity sensor has small volume and good linearity, but the signal is small, 0.2 P/%Rh. The capacitance signal is easily affected by the distributed capacitance, and the capacitor signal is not handled as well as the resistance and voltage signals. Therefore, when designing the circuit The polymer film humidity sensitive capacitor and the pre-processing circuit are mounted on a small printed circuit board, and the pre-processing circuit first converts the capacitance signal into a pulse signal, and then sends the lead to the collector for further processing, thereby overcoming the lead capacitance. The impact on the sensor. The block diagram of the humidity acquisition module is shown in Figure 3(a).

2.3 Temperature Acquisition Module

The entire temperature acquisition module can be divided into five parts: sensor AD590, operational amplifier LM324, A/D converter TLC1549, AT89S52 and power supply. The MCU will amplify the collected analog temperature signal and send it to TLC1549 for analog-to-digital conversion, and then send it to the DSP from the I2C bus through 2051 for processing. The block diagram of the temperature acquisition module is shown in Figure 3(b).

2.4 pH acquisition module

The skin pH is collected using an advanced skin-type electrode sensor. It directly converts the pH of the skin into a voltage form output. The MCU sends the processed data to the DSP processor through the I2C bus. The block diagram of the pH acquisition module is shown in Figure 3(c).

2.5 Communication between DSP and USB

CY7C68013 is a microprocessor integrated with USB2.0 protocol introduced by Cypress Semiconductor, also known as EZ-USBFX2 (referred to as FX2). The device is a bridge between the data acquisition and processing system and the computer for data exchange. The FX2 integrates a USB 2.0 transceiver, SIE (Serial Interface Engine), an enhanced 8051 microcontroller, 8.5 KB of RAM, 4 KB of FIFO memory, and a programmable peripheral interface. This original architecture of FX2 enables data transfer rates of up to 56 MB/s, the maximum bandwidth allowed by USB 2.0. The interface circuit of FX2 and TMS320VC33 is shown as in Fig. 4.

2.6 Communication between DSP and MCU

The AT89S52 and TMS320VC5402 work independently, and their information and data exchange are realized through shared external memory. The signal communication between them is realized through hard connection and software judgment.

The external memory uses the CY7C133, which is a high-speed 2K & TImes; 16-bit static asynchronous dual-port RAM with a storage speed of 25ns. It has two separate address lines, data lines, and control signal lines that allow data from two control devices to communicate through a commonly connected memory. The dual port RAM allows two controllers to simultaneously read any memory location (including reading the same unit simultaneously), but does not allow simultaneous writes or read and write of a uniform address location.

For the TMS320VC5402, the corresponding address of the data memory CY7C133 is 4000H to 47FFH.

For the AT89S52, the corresponding address of the data memory CY7C133 is 2000H to 27FFH.

2.7 system power supply

Ethernet Cable Wiring

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