RU2697715C1 - Microcontroller capacitance measuring device for built-in computer systems - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment, in particular, to devices for measurement of physical values by capacitive sensors, and can be used in built-in computer control and monitoring systems. Microcontroller capacitance measuring device for built-in computer systems includes resistor 1, capacitive sensor 2, resistor 3, reference capacitor 4, microcontroller 5 and computer 6. Capacitive sensor 1 and reference capacitor 4 are connected to common wire by first plates, second plates of capacitive sensor 1 and reference capacitor 4 are connected to first outputs of resistors 1 and 3, respectively, second leads of resistors 1 and 3 are connected to outputs of first and second pulse-width modulators (PWM), built-in into microcontroller 5 (not shown in PWM drawing), second plates of capacitance sensor 2 and reference capacitor 4 are connected to first and second inputs of analogue multiplexer built into microcontroller 5 (in the drawing analogue multiplexer is not shown), analogue multiplexer output is connected to the analogue-to-digital converter (ADC) built in microcontroller 5 input (not shown in the ADC drawing), computer 6 is connected via digital serial interface to microcontroller 5.

EFFECT: high accuracy of conversion and broader functional capabilities of the device owing to the possibility of using a more sophisticated algorithm for converting capacitance to binary code, as well as high computational and info-communication capabilities of the device by introducing a computer.

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Description

FIELD OF THE INVENTION

The invention relates to measuring equipment, in particular, to devices for measuring physical quantities by capacitive sensors and can be used in embedded computer monitoring and control systems.

State of the art

A device for measuring electric capacitance is known, comprising two one-vibrators connected according to a circular oscillator circuit, capacitors of a measured capacitance and an exemplary capacitor, two integrating links connected to the outputs of the corresponding one-vibrators, an indicator connected between the outputs of the integrating links are included in the timing circuits of the first and second single vibrators . A constant voltage is formed at the output of the device, which depends on the change in the measured capacitance and is reflected by an indicator (see Pat. RF No. 2156472, class G01R 27/26).

A disadvantage of the known solution is limited functionality.

A device for measuring non-electric quantities by capacitor sensors is known, which contains a microcontroller, an indicator, first and second generators, during which the capacitive sensor and a reference capacitor are respectively connected, the outputs of the generators are connected to the inputs of the microcontroller, the indicator is connected to one of the ports of the microcontroller (see US Pat. RF No. 2214610, class G01R 27/26).

A disadvantage of the known solution is limited functionality.

The closest in technical essence to the claimed technical solution and adopted by the authors for the prototype is a microcontroller device for measuring the shaft speed, containing a microcontroller, indicator, first and second resistors, a capacitive sensor and a reference capacitor, which are connected to the common wire by the first plates, and the second capacitive plates the sensor and the reference capacitor are connected, respectively, to the first and second inputs of the analog comparator of the microcontroller and to the first conclusions of the first and the second resistors, the second terminals of which are connected to the outputs of the microcontroller, the indicator is connected to one of the ports of the microcontroller (see US Pat. RF No. 2378658, class G01R 27/26).

A disadvantage of the known solution is the low accuracy of the transformations and limited functionality, due to the imperfect algorithm for converting capacity to binary code, as well as the limited computing and information and communication capabilities of the device.

Disclosure of invention

The objective of the invention is to develop a capacitance measuring device for embedded computing systems with improved conversion accuracy and enhanced functionality by using a more advanced algorithm for converting capacitance into binary code, as well as increasing the computing and information and communication capabilities of the device by introducing a computer.

The technical result is achieved by the fact that in the microcontroller measuring device of the capacitance for embedded computing systems, containing a microcontroller, a capacitive sensor, a reference capacitor, the first and second resistors, the capacitive sensor and the reference capacitor are connected to the common wire by the first plates, the second plates of the capacitive sensor and the reference capacitor connected, respectively, to the first terminals of the first and second resistors, a computer is introduced, and the second terminals of the first and second resistors connected to the outputs of the first and second pulse-width modulators built into the microcontroller, the second plates of the capacitive sensor and the reference capacitor are connected, respectively, to the first and second inputs of the analog multiplexer built into the microcontroller, the computer is connected via a digital serial interface to the microcontroller.

Brief Description of the Drawings

In FIG. presents a structural diagram of a microcontroller measuring device capacitance for embedded computing systems.

The implementation of the invention

The microcontroller measuring device of the capacitance for embedded computing systems contains (Fig.) A resistor 1, a capacitive sensor 2, a resistor 3, an exemplary capacitor 4, a microcontroller 5, and a computer 6. The capacitive sensor 1 and the exemplary capacitor 4 are connected to the common wire with the first plates, the second plates of the capacitive the sensor 1 and the reference capacitor 4 are connected, respectively, to the first terminals of the resistors 1 and 3, the second terminals of the resistors 1 and 3 are connected to the outputs, respectively, of the first and second pulse-width modulators (PWM) integrated in the microcontroller 5 (not shown in Fig. PWM), the second plates of the capacitive sensor 2 and the reference capacitor 4 are connected, respectively, to the first and second inputs of the analog multiplexer integrated in the microcontroller 5 (the analog multiplexer is not shown in Fig.) , the output of the analog multiplexer is connected to the input of an analog-to-digital converter (ADC) built into the microcontroller 5 (the ADC is not shown in Fig.), the computer 6 is connected via a digital serial interface to the microcontroller 5.

Microcontroller measuring device capacitance for embedded computing systems operates as follows.

The microcontroller 5, in accordance with the program, tunes the first and second PWMs to a given frequency of generating pulse-width signals (PWM signals) with the specified duty cycle and starts both PWMs that operate synchronously. The resistances of resistors 1 and 3, as well as the capacitance of the capacitive sensor 2 and the reference capacitor 4 are selected so that at a given frequency of the PWM signals, transients in the RC circuits formed by these elements last from one to three time constants of the RC circuits. Microcontroller 5 executes the algorithm sequentially step by step:

Step 1. The microcontroller 5 connects the first input using an analog multiplexer, to which the first lining of the capacitive sensor 2 is connected to the ADC input and performs several hundred conversions, the results of which are stored in RAM.

Step 2. The microcontroller 5 processes the results of the ADC conversions and finds the smallest and largest values, then calculates the difference between these values, so the microcontroller 5 determines the magnitude of the voltage change across the capacitive sensor 2 and stores this value in memory.

Step 3. The microcontroller 5 connects the second input using an analog multiplexer, to which the first lining of the reference capacitor 4 is connected to the ADC input and performs as many conversions as it did in step 1, it stores the results of the transformations in RAM.

Step 4. The microcontroller 5 performs the same actions as in the implementation of step 2 with the difference that determines the magnitude of the voltage change across the sample capacitor 4 and stores this value in memory.

Step 5. The microcontroller 5 determines the difference between the voltage span of the sample capacitor 4 and the capacitive sensor 2, this difference depends on the measured capacitance of the capacitor sensor 2. With an increase in the capacitance of the sensor 2, the voltage span on it decreases, and when the sensor capacitance decreases, the voltage span on it increases .

Step 6. The microcontroller 5 sends the conversion result via a digital serial interface to the computer 6, which displays this result on the monitor.

Step 7. The microcontroller 5 proceeds to step 1.

Computer 6 can save the data obtained from the microcontroller 5 in memory for subsequent analysis, and can also transmit via info-communication networks to any geographical point in the world where the second computer is configured to receive this information.

Computer 6 allows you to quickly write to the program memory of the microcontroller 5 new modified programs, which also extends the functionality of the proposed device.

The microcontroller 5 is able to change, in accordance with the program, the frequency of the PWM signals and their duty cycle, which is necessary for the correct coordination of the parameters of the RC circuits (for example, the time constant of the RC circuits) and the parameters of the PWM signals.

Sometimes it is required to carry out measurements at several frequencies, especially when measuring the dielectric constant of a material located between the plates of a capacitive sensor, for example, when measuring the moisture content of seeds of agricultural crops. It is known that the dielectric constant of these materials depends on the frequency of the electric field between the capacitor plates.

Advantages of the invention compared to the prototype: thanks to the introduction of new connections, a more advanced algorithm for converting capacitance to binary code is implemented, which increases the accuracy of the device; by introducing a computer, computing and information and communication capabilities have been increased, which expands the functionality of the device.

Claims (1)

A microcontroller measuring device of capacitance for embedded computing systems, comprising a microcontroller, a capacitive sensor, a reference capacitor, first and second resistors, the capacitive sensor and the reference capacitor being connected to the common wire by the first plates, the second capacitor sensor and reference capacitor plates are respectively connected to the first terminals of the first and a second resistor, characterized in that the computer is additionally introduced, and the second terminals of the first and second resistors are connected s to the outputs of the first and second pulse-width modulators built into the microcontroller, respectively, the second plates of the capacitive sensor and the reference capacitor are connected respectively to the first and second inputs of the analog multiplexer integrated in the microcontroller, the computer is connected via a digital serial interface to the microcontroller.

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