Based on Energymicro's 32-bit Cortex-M3 core ultra-low-power microcontroller EFM32 and ACAM's highly integrated TDC-GP21 chip's ultrasonic heat meter solution, the EFM32's ultra-low power consumption and high computing power can be fully utilized. The features and high-precision measurement capabilities of the GP21 will make it the best choice for ultrasonic heat meter solutions.
Master control and display section
The ultrasonic master MCU adopts EFM32TG840F32, which is based on ARM's 32-bit Cortex-M3 core design. Compared with the traditional 8-bit and 16-bit microcontrollers, it has higher computing and data processing capabilities and higher code density. , lower power consumption. The actual data shows that the EFM32TG840 requires only 4 core clock cycles to perform 32-bit multiplication, and only 8 core clock cycles for 32-bit division, while the 16-bit microcontrollers used on the corresponding thermal table require 50 and 465 clock cycles, respectively. . The data collected on the time data conversion chip TDC-GP21 is 32-bit length, so it is a 32-bit data operation in both calculation and heat calculation.
The EFM32TG840 has five low-power modes of EM0-EM4. In EM2's low-power mode, the microcontroller can still implement RTC operation, LEUART, LETIMER and LESENSE communication or control functions, while power consumption only needs 900 A. Moreover, it has a flexible wake-up mode and autonomously working PRS system, which can be awakened by external I/O, I2C communication interface, LEUART communication signal, and the like.
The EFM32TG840 integrates 8&TImes; a 20-segment LCD driver that meets the needs of a direct-drive ultrasonic heat meter LCD screen with a power consumption of only 550nA. The EFM32TG840's LCD driver integrates a voltage boost function and a contrast adjustment function to monitor the VDD voltage on the chip's internal VCMP voltage comparator, and to turn on the LCD boost and contrast adjustments to achieve good LCD performance even with the system battery. A voltage drop occurs when the usage time increases.
Figure 2 Master MCU and display circuit
The I/O of the EFM32TG840 can be set to low power mode wake-up and GPIO interrupt mode, so external operation buttons can be used for interactive control actions under low power conditions.
TDC-GP21 ultrasonic acquisition part
The TDC-GP21 is a new generation of digital time converters used by ACAM in Germany at the end of November 2011 for the measurement of ultrasonic heat meters. The TDC-GP21 chip is packaged in QFN32. In addition to the TDC-GP2 function, it also integrates the signal processing analog part required for ultrasonic heat meters, such as analog switches and low noise chopper stabilization (automatic temperature and voltage correction) analog signals. Comparators. The TDC-GP21 temperature section integrates a Schmitt trigger, which can be directly connected to the temperature sensor and the reference resistor for high-precision measurement. The performance of the measurement far exceeds the requirements of the heat meter. The 7x32bit EEPROM unit can be used to store the ID information and configuration register information of the heat meter.
The TDC-GP21 requires two supply voltages, the core voltage VCC and the I/O voltage Vio. In this solution, the two supply voltages recommended by ACAM are powered by the same voltage source, and the decoupling dual-channel filter circuit is added. In order to achieve the effect of reducing system noise. Other parts of the circuit, such as the transducer, the connection of the PTC resistor, and the connection of the crystal are all built using the official reference circuit provided by the manufacturer. In terms of clock, the TDC-GP21 will output a 32.768KHz clock and provide a low-frequency clock for the EFM32TG840F32, saving the low-frequency crystal of the master MCU.
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