Circuit and method for measuring resistance of variable resistor

Abstract

The invention aims to provide a circuit and a method for measuring resistance of a variable resistor. The circuit comprises single-chip microcomputers, a capacitor, a to-be-tested variable resistor Rx and a standard resistor R1. One end of the capacitor C is connected with the single-chip microcomputer GP0, and the other end of the capacitor C is connected with the ground. One end of the standard resistor R1 is connected with one end of the capacitor C, and the other end of the standard resistor R1 is connected with the single-chip microcomputer GP1. One end of the to-be-tested variable resistor Rx is connected with the single-chip microcomputer GP2, and the other end of the to-be-tested variable resistor Rx is connected with the other end of the standard resistor R1. The other end of the to-be-tested variable resistor Rx is connected with the other end of the standard resistor R1. According to the invention, a charging time T1 of a charge and discharge loop of the standard resistor R1 and the capacitor C and a charging time T2 of a charge and discharge loop between the serially-connected to-be-tested variable resistor Rx and the standard resistor R1 and the capacitor C are measured, and the resistance of the to-be-tested variable resistor Rx is calculated through a mode of Rx=R1*(T2-T1) / T1. The method provided by the invention solves the contradiction between measurement precision and measurement time in the circuit for measuring the resistance of a variable resistor by measuring the charge and discharge time of a capacitor in the prior art, and can obtain a good measurement result for a small variable resistor.

Description

technical field [0001] The invention relates to the field of electronic circuit measurement, in particular to a circuit and method for measuring the resistance value of a variable resistor. Background technique [0002] The RC charging and discharging circuit is a commonly used basic circuit. According to Kirchhoff's law and advanced mathematics, when the power supply E charges the capacitor C through the resistor R, the voltage Vt on the capacitor C at any time can be calculated by the formula Vt = V0 + (Ve –V0)*[1 – exp(-t / RC)] is obtained. Where Ve is the voltage of the power supply E, and V0 is the initial voltage before the charging of the capacitor C starts. When the initial voltage of the capacitor C is 0, that is, when V0=0, the above formula can be simplified as: Vt = Ve *[1 – exp( -t / RC)] (1). [0003] Chinese Utility Model Patent No. 201320780623.6 discloses a circuit that uses the above principle to measure the resistance of a variable resistor. The circuit dia...

AI Technical Summary

Problems solved by technology

This method has the following defects: the solution method requires complex calculations to obtain relatively accurate results; it ignores the discharge effect of R1 when charging the capacitor, and the calculated value will have a large error when Rx is close to R1; Rx is greater than the calibration resistor R1, the port connected to R2 is set as an input port, and when the port connected to Rx is an output port, the input port connected to R2 of the microcontroller will never detect the transition from low level to high level, limitations Big

[0006] This measurement method also has major defects: in actual use, it is necessary to measure the resistance of multiple variable resistors at the same time, generally there are four or more, and in order to reduce the accidental error during measurement, it is necessary to repeat the same loop. Multiple measurements, so in order to meet the requirements of real-time response speed, the measurement time must be small enough, that is, the selected capacitance C value must be small enough, generally 0.01uF or less; in such applications, such as remote control aircraft model control handle, The cost of the single-chip microcomputer MCU used is limited. The speed of these single-chip microcomputers is below 50M, and their single instruction cycle is not less than 0.02uS. Considering that the single-chip microcomputer needs at least several cycles to complete the start and stop of the single-chip timer, the input For port level acquisition and level judgment, the measurement time error will be above 0.1uS. In order to obtain credible measurement results, the measurement results must be much larger than the measurement error, generally more than 10 times, so that the influence of the error can be ignored. Formula 1 shows that when the capacitance C is 0.01uF, Vt is 1 / 2 of Ve, and the MCU speed is 50M, only when the resistance is greater than 150 ohms can the measurement time change of more than 1uS be obtained. In order to measure a smaller resistance, that is For higher precision, a larger capacitor C must be selected, such as 0.1uF or larger

[0007] In summary, it can be seen that there is a contradiction between the measurement accuracy and the measurement time in the currently known circuit that measures the resistance of the variable resistor by measuring the charging and discharging time of the capacitor, so that the circuit is commonly used in some applications that do not require high precision or real-time performance. In occasions with low requirements, at the same time, when the resistance to be measured is small in this known circuit, because the charging and discharging time of the capacitor is too short, for example, it is close to or less than the measurement error time, and it is basically impossible to measure

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