Digital voltmeter 200V

0~20V range DC meter link: https://lceda.cn/mimiww/shuo-zi-dian-ya-biao-tou This time it has been increased to 0~200V. Modifying the value of the voltage dividing resistor can further expand the range. The accuracy is one digit after the decimal point. It actually feels faster than the response speed of the meter.

• This design is a voltmeter based on the chip ICL7107. The measuring range is 0~200V, and the measuring range can be expanded.
• ICL7107 is an analog-to-digital conversion chip with high precision, low noise, small temperature drift, high stability, and long life. It has segment code output and can directly drive the digital tube without any program.
• This project mainly includes ICL7107 drive circuit, four common anode digital tube circuits, etc.
• 5V power supply, the voltage to be measured is connected through another terminal
• After the component welding is completed, there is no short circuit in the meter measurement. When the power is turned on, pin 1 is 5V, pin 26 is about -3V~-4V, and pin 36 is 1V, which is the normal state. At this time, the digital tube should display three 0s. If not, please check the components and welding conditions again
• When using it for the first time, you need to confirm the position of the decimal point. You only need to determine the position of the jumper cap. In this example, you need to add the short-circuit cap at the bottom. The adjustable resistor is used to accurately control the digital tube display against the voltmeter. Adjustment, the button is a test function, when pressed, all indications will be cleared.
• The chip is shown as out of stock in Lichuang Mall, but the package and information are available and can be used directly. To purchase the chip, you need to go to Taobao to have a look.
• Circuit composition:
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1. Circle 1 is an oscillation network used to provide a clock signal. The clock frequency is 45kHz. The more accurate the clock signal, the better, so try to choose resistors and capacitors with higher precision.
2. Circle 2 is the reference signal circuit, which provides a high-precision reference voltage. In this example, the maximum input voltage of the chip pin is 2V, and the voltage of pin 36 is accurate 1V. The capacitor used in C11 should not use ceramic capacitors.
3. Circle 3 is the input terminal of the voltage signal to be measured. The measured voltage first passes through a 1M resistor so that the signal is not distorted. After being filtered by a 103 capacitor, the accurate voltage is input to the chip for measurement.
4. Circle 4 is the integral network of the chip, which is a resistor-capacitor network composed of 47nF, 470K, and 220nF. In order to measure accurately, the capacitors and resistors should use high-precision and stable components. Try not to use ceramic capacitors. Tantalum is used here. Capacitors and CBB capacitors
5. Circle 5 is a negative voltage generating circuit, because the chip's required power supply voltage is ±5V, but the voltage of the negative voltage input pin 26 is considered normal between -3V and -5V and can work normally. Regarding the negative voltage generating circuit, Use an NPN transistor, two resistors and an inductor for signal amplification. Because pin 38 of the chip will generate an oscillation signal, connect it in series with a 20K - 56K resistor to the base of the transistor, and connect a resistor in series with the collector. (protective effect) and an inductor (increase AC amplification factor), the voltage of the collector is preferably 2.4V~2.8V. In this way, there will be an amplified AC signal at the collector of the triode, and this signal passes through two 4.7 uF and two diodes form a voltage doubler rectifier circuit, and negative voltage can be obtained for the chip.
6. Circle 6 is a voltage divider circuit, because the full-scale range of the chip is 2 V in circle 4, and it needs to be used after expanding the range. In this example, the voltage to be measured is reduced by 100 times and then supplied to the chip for measurement, V = VIN * R19 / ( R19+R20+R21). If you need to expand the range, you need to calculate and change the resistance of the resistor. The resistance of the input voltage resistor cannot be too small, otherwise it will cause a decrease in accuracy and cause hidden dangers. The input voltage should not be too large, which is too dangerous. If you need to measure a larger voltage, be sure to add a varistor at the input end.
7. Negative voltage circuit simulation: This is rarely used. If the end time is 5ms, it cannot be increased. If you select 6ms or above, the file will be too large. However, if the time increases, the voltage will definitely continue to decrease. The actual measurement is -3.7V.