Based on XMEGA portable design of electrolyte Analyzer (1)

Electrolysis quality Analyzer for determination of biological specimens such as blood serum, plasma, blood and the value in the urine diluted potassium (K), sodium (Na) and chlorine (C1), calcium (Ca), pH, etc., and providing standardized by computational ionized calcium (nCa), total calcium (TCa), in the clinic has a great significance.

Since the 1980s, Olympus, Ciba-Corning products into China abroad, domestic electrolyte Analyzer rapid follow up, and developed a number of performance products. In recent years, with some unexpected events occur (such as: Wenchuan earthquake), portable medical instruments demand increases greatly, portable electrolyte Analyzer is one of them.

Here a ATMEL used company launched a high-performance SCM XMEGAl28 as the core device designed by battery-powered portable electrolyte Analyzer, can meet the demand for field use.

1 XMEGA introduction

XMEGA is an 8-bit AVR microprocessor upgrade version of strong performance.

Second generation picoPower technology, XMEGA uses, is the only real use 1.6 V operating voltage of Flash microcontrollers. Ultra-low power consumption of the devices, and with fast 12-bit analog capabilities, 1 DMA controller, 1 x innovation event system, as well as 1 AES encryption engine, all without the need to consume CPU resources, to minimize power consumption and improve system performance. XMEGAl28 microcontroller Flash memory capacity of up to 128 Kb, 100 pin SMD package, operate at 1.6 ~ 3.6 V, 32 MHz frequency processing performance can reach 32 MI/s.

Because the internal XMEGAl28 rich resources and strong performance.

Make it very suitable for embedded systems. The portable electrolyte Analyzer uses XMEGAl28 as core microprocessor, makes the whole system peripheral devices greatly reduced, while reducing costs and improving system security and reliability. XMEGAl28 larger program storage space to meet electrolyte Analyzer of a large number of software code.

2 system hardware design

The system is based on a microprocessor, ATxmegal28Al peripheral connection is displayed, press the key, printer sensor zoom, cartridges, power supply, communication module, its hardware design structure diagram shown in Figure 1.

Display part adopts 320x240 Generic LCD, directly driven by ATxmega128Al bus, providing users with more intuitive information, also makes the operation more convenient.

Embedded micro printers using micro siupo company thermal printer, easy field output document type information directly from the bus driver ATxmegal28A1.

2.1 sensor conditioning amplifier

The Analyzer of the sample solution by polymer membrane sensor measurement of signal amplitude is very small, in-between 250 ~ 250 mV to direct A/D conversion.

Therefore, you need to make the analog signal conditioning amplifier. In circuit design, and ion-selective electrode high internal resistance matching, CA3140 integration adopted operational amplifier as level zoom, secondary amplification using high-precision low-drift amplifier HAl7741 operations.

As shown in Figure 2, uses three operational amplifier consisting of measuring amplifier, the preceding 2 high input impedance of the CA3140 constitute a differential input.

Back-end of HAl7741 is actually a differential gain follower, its approximate to 1. In order to ensure the accuracy of the amplifier, resistance select negative feedback high accuracy and low temperature drift of precision resistance and circuit closed-loop gain is not too large. At the same time to prevent the circuit board surface leakage current, the Board carried out a partial outline. In order to be able to work under field conditions, the Board also conducted a moisture-proof electronic processed and shield.