Circuit Design of Automatic Range Voltmeter Based on STM32

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Overview:
This paper introduces a design scheme of an automatic range voltmeter based on STM32. The automatic range voltmeter designed in the scheme can accurately measure DC voltage and AC voltage, and has the characteristics of high measurement accuracy and strong anti-interference ability.
The entire system in the solution can be powered by a 9V battery, enabling low power and portable functions. AC measurement is measured by converting the AC signal into DC voltage with the AD637 true RMS conversion chip; input voltage conversion is performed with an inverting amplifier with clamp protection, achieving 10MΩ input impedance and high safety. The key components in the circuit use TI's precision operational amplifier OPA07 and instrumentation amplifier INA128 to achieve high-precision measurement. The ADC uses STM32f103ZET6 on-chip 12-bit AD to achieve low power consumption and automatic range switching.

0 INTRODUCTION In intelligent instruments, automatic range conversion technology is often used, which allows the instrument to automatically select the most appropriate range for high-precision measurement in a short period of time. The implementation of autoranging is generally achieved by controlling the attenuation amplification of the input signal. In terms of the voltmeter, the input measurement voltage is greater than the input range of its AD converter, so its range switching is basically the process of signal attenuation multiple switching.

1. System overall scheme and working principle System function block diagram shown in Figure 1. STM32F103ZET6 processor is the core device of this system, which is responsible for controlling the normal operation of the whole system, including reading the result of AD conversion and control of 200mV and 2V gear position; button input action response; segment LCD drive; range automatic conversion control Wait.

The input voltage signal passes through the range conversion module and becomes a voltage that can be sampled normally by the ADC analog input. The function of the AC voltage measurement module is to convert the measured AC voltage to the corresponding RMS value. The function of the key input is to input various values ​​when switching between different measurement modes and calculating the relative error.

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