Design of Ultra Low Power Ultrasonic Heat Meter Circuit Module Based on GP21+EFM32

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Based on the 32-bit Cortex-M3 core ultra-low-power microcontroller EFM32 and ACAM's highly integrated TDC-GP21 chip, the ultrasonic heat meter solution can fully utilize the EFM32's ultra-low power consumption and high computing power. GP21's high-precision measurement capability will be 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. It can be seen that the EFM32TG840 can make the ultrasonic heat meter have better computing performance, so that the whole machine can shorten the running state of the running state and achieve the effect of reducing the running power consumption.

The EFM32TG840 has five low-power modes of EM0-EM4. In the low-power mode of the EM2, 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; 20-segment LCD driver to meet the needs of direct drive ultrasonic heat meter LCD screens, while consuming only 550nA. The EFM32TG840's LCD driver integrates a voltage boost function and a contrast adjustment function to monitor the VDD voltage in the on-chip VCMP voltage comparator, and to turn on the LCD boost and contrast adjustment in a hierarchical manner. The LCD phenomenon is good even if the system battery is used. 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.