Built-in digital voltmeter with a measurement range of -199,9 ... +199,9 mV. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Measuring technology

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An embedded digital voltmeter can be used as an indication device in measuring instruments [5], to control the output voltage of power supplies, and also to work with various electronic converters [1, 2, 4, 7]. Two types of voltmeters have been developed - with LED and liquid crystal indicators.

Specifications:

• the measured voltage is constant, the measurement range is 0 ... +199.9 mV, the number of readings is 3 per second
• measurement error no worse than 0.2%
• voltmeter power supply is bipolar (+5 volts), power consumption is not more than 2100 mW
• operating temperature range +10 0C ... +35 0C, relative humidity up to 80% at 20 0C
• dimensions not more than 100 x 75 x 40 mm3
• weight not more than 100 g

Electrical circuit diagram (click to enlarge)

The voltmeter is assembled according to a typical circuit [6] on a DA1 KR572PV2A chip (analogue of ICL7107), which performs the function of an analog-to-digital converter (ADC) with double integration, automatic zero correction and input signal polarity detection. A 3.5-decade digital display with 7-segment LED indicators of the ALS321B (ALS324B) type is directly connected to the microcircuit output. The reference voltage source (ION) +100 mV is assembled according to the R1R2 resistive divider circuit, connected directly to the +5 V supply voltage source, which must have sufficient stability. The operating mode of the ADC is determined by the parameters of the attachments R4, R5, C1 - C4. The measured voltage is applied to the contacts IN+, IN-, the potential of which can be arbitrary within the range of supply voltages.

Design

The voltmeter consists of two printed circuit boards, on one of which an ADC with attached elements is assembled, and on the other - a digital display. The boards can be attached to each other at the required angle or can be spaced apart. The connection is made by soldering or using a cable.

Specifications:

• the measured voltage is constant, the measurement range is -199.9 ... +199.9 mV, the number of readings is 3 per second
• measurement error no worse than 0.2%
• voltmeter power supply is bipolar (+5 volts), power consumption is not more than 12 mW
• operating temperature range +10 0C ... +35 0C, relative humidity up to 80% at 20 0C
• dimensions not more than 100 x 75 x 40 mm3
• weight not more than 100 g

Electrical circuit diagram (click to enlarge)

The voltmeter is assembled according to a typical circuit [6] on a DA1 KR572PV5A chip (analogous to ICL7106), which performs the function of an analog-to-digital converter (ADC) with double integration, automatic zero correction and input signal polarity detection. A 3.5-decade digital display with 7-segment liquid crystal indicators of the IZhTs5-4/8 type is directly connected to the microcircuit output. The reference voltage source (ION) +100 mV is assembled according to the R1R2 resistive divider circuit, connected directly to the +5 V supply voltage source, which must have sufficient stability. The operating mode of the ADC is determined by the parameters of the attachments R4, R5, C5 - C9. The measured voltage is applied to the contacts IN+, IN-, the potential of which can be arbitrary within the range of supply voltages. Capacitors C1 - C4 act as filters in power circuits. The circuit on the transistor VT1 provides the supply of rectangular bipolar pulses to the decimal point of the liquid crystal display.

Design

The voltmeter consists of two printed circuit boards, on one of which an ADC with attached elements is assembled, and on the other - a digital display. The boards can be attached to each other at the required angle or can be spaced apart. The connection is made by soldering or using a cable.

Voltmeter power supply circuit from a 12,6 volt unipolar source (battery)

To obtain a bipolar voltage of +5 volts from a unipolar +12.6 volts (battery), two voltage stabilizers are used: serial - DA1 (KR142EN5A, 7805) and parallel - DA2 (TL431). Transistor VT1 (KT837U) is used to increase the load capacity of the parallel stabilizer. Resistor ratings: R1 - 680 Ohm, R2 - 680 Ohm, R3 - 62 Ohm, R4 - 300 Ohm; capacitors: C1, C2 22 uF 16 V.

Development status:

The built-in digital voltmeter is supposed to be used in the design of various measuring instruments operating from the AC mains or the vehicle's on-board network, power supplies and batteries.

Sources of

1. Absolute linear displacement sensor of the range 0 - 10 mm with a linear variable differential transformer, imlab.narod.ru/MechSys/LVDT/LVDT_01.htm
2. Differential capacitive angular and linear displacement sensor, imlab.narod.ru/Electron/C_Sensor/C_Sensor.htm
3. Ivanov, V.I. and additional - M.: Energoatomizdat, 2. - 1989 p.: ill.
4. Inductive position sensor and small linear displacements, imlab.narod.ru/Electron/L_Sensor/L_Sensor.htm
5. Devices for measuring magnetic fields, imlab.narod.ru/M_Fields/Magn_Meas/Magn_Meas.htm
6. Fedorkov B. G., Telets V. A. DAC and ADC microcircuits: operation, parameters, application. - M.: Energoatomizdat, 1990. - 320 p.: ill.
7. Electronic signal converter for a differential capacitive sensor, imlab.narod.ru/Electron/EP_C/EP_C.htm

Publication: imlab.narod.ru

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