Multichannel remote voltmeter on the microcontroller. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Multichannel remote voltmeter on the microcontroller. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Microcontrollers

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A multi-channel remote voltmeter is a device that allows you to remotely measure the values of alternating sinusoidal voltages from several different sources (six channels in this implementation) and present the information received on six three-digit seven-segment indicators.

The development of the device is due to the need for constant monitoring of the power supply of equipment located at some distance from the location of a person. Currently, the device is used to control three phases of the input voltage supplied to the industrial normalizer and three phases of the removed voltage. The distance from the measurement point to the indication point is 800m.

Structurally, the voltmeter is made in the form of two modules - a measurement and transmission module located directly at the measurement site, as well as a reception and indication module installed at the workplace. Communication between the two modules is organized using a pair of wires (currently a telephone pair is used). The communication channel is galvanically isolated from the device nodes that are under dangerous voltage, information is transmitted by a current signal with a value of up to 30mA.

Multichannel remote voltmeter on the microcontroller. Structural scheme

Device Specifications:

- Measured voltage: 100-330V AC, 50Hz;
- Interval between measurements: 0.5 sec. (all 6 values are updated);
- Supply voltage of the receiving and indication module: 7-25V DC;
- Breakdown voltage of galvanic isolation of modules: 5.0 kV;
- Maximum measurement error: ±1,5%.

(click to enlarge)

Analog-to-digital conversion is performed using an ADC integrated into the ATmega8 microcontroller. To measure the effective value of the alternating voltage, an algorithm for detecting the peak of a sinusoidal signal and its subsequent multiplication by the amplitude coefficient of the sinusoid is implemented.

The measurement and transmission module is powered through a transformerless power supply from the first channel of the measured voltage. If the voltage on this channel drops below 90V, the module switches off. LED HL1 is used to indicate the process of transmitting information to the receiving module.

(click to enlarge)

The reception and indication module is powered from an external source of direct voltage 7-25V.

In normal mode, all indicators display the measured voltage values corresponding to a specific channel. If there are no messages from the transmitter for more than 2 update periods (approximately 1,4 sec.), the word "Err" is displayed on all indicators, which indicates a violation of the communication channel, or a malfunction of the transmitter. The indication returns to normal mode after receiving the next message. A decrease in voltage on any of the channels, except for the first, below 100V leads to the indication of a dash "---" on the corresponding indicator, the remaining channels are displayed in normal mode.

In this version of the voltmeter, only AC voltage is measured, however, by making minimal changes to the software part of the MC of the transmitting module, as well as by changing the values of the voltage divider resistors R5-R10 and R11-R16, it is possible to measure DC voltage on all or several individual channels.

Microcontroller firmware, printed circuit boards in GIF and LAY (SprintLayout) format, as well as photos of the finished device can be downloaded here (430 kb).

Author: Lukashchuk Anton Sergeevich, aslukashuk[dog]gmail.com; Publication: cxem.net

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