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Digital voltmeter circuit using ICL7107

Published on Feb 14 2011 // Special measuring and display circuits

Digital voltage meter (digital panel meter) is the current electronic, electrical, instruments, meters and measurement of a large number of basic measurement tools used in digital voltage meter on the books and has become so popularized. Here’s a show by the ICL7106 A / D converter circuit digital voltage meter (digital panel meters) circuit, is a most common and basic circuits.
Similarly with the ICL7106 ICL7107, the former using the LCD liquid crystal display, which is driven LED digital tube as the display, in addition to the basic application of the two are interlinked.

Digital voltmeter circuit using ICL7107 1

Circuit, only the use of a DC9V batteries, digital voltage meter to be normal use. Number of components as illustrated, the meter-scale range is ± 200.0mV. When the voltage to be measured ± 200mV, the signal from the V-IN-ended input, when the need to measure ± 200mA of current, the signal from the A-IN-ended input, do not take any additional switch, you can get the contents of the two measurements.

There are also many occasions, I hope the digital voltmeter (digital panel meter) and larger range, then the two components only need to change the value, you can achieve a range is ± 2.000V. Change the location and number of components shown below two pins 28 and 29:

With a digital voltmeter in the (digital panel meters), the accordance with the following icon, give it a shunt resistor configuration, you can achieve multi-range digital current meter, sub-file from ± 200uA to ± 20A. But beware: 20A high current file in use when the switch can not switch to another range, a measurement should be specially configured socket, switch to prevent burning.

And multi-range ammeter corresponds to the frequent use of multi-range voltage meter, according to the following chart to configure a component resistors, you can get ranges from ± 200.0mV to ± 1000V multi-range voltmeter.

Measuring resistance is as important as measuring current or voltage, commonly known as the "three by the table," made use of digital voltage meter multi-range resistance meter, using the "ratio method" measurement, so that it compared to a pointer with a multimeter resistance measurement very accurate precision, and power a small icon in the configuration under a set of resistance called "Jizhun resistance", is obtained by switching all Jiedian different base resistance, then Vref voltage to be measured resistor the Vin voltage "proportional reading", when Vref = Vin, the display is Vin / Vref * 1000 = 1000, in accordance with the decimal point on the need to light up the screen, you can directly read the measured resistance is coming.
  Digital multimeter in the product, in order to save costs and simplify the circuit, measure the current shunt resistor voltage divider and measuring resistor and the measurement of resistance is often the same set of baseline resistance resistance. Not be discussed here, the circuit digital multimeter, just to help the reader to use a feature in a separate, you can have some reference.

Digital voltmeter circuit using ICL7107 2

The figure is 10 times that of a simple amplifier circuit, operational amplifiers using a high accuracy of the OP07, use it, you can put 0 ~ 200mV of voltage amplification to the 0 ~ 2.000V. Digital voltmeter in use when the range is 2.000V, (for example, the composition ICL7135 41 / 2 digital voltage meter, the basic range is 2.000V.) Particularly useful.
  If it is used in the basic range is ± 200.0mV the digital voltage meter on the equivalent to 10 times higher resolution in some measurement, the sensor signal often feel too small, then, can be considered in the digital voltmeter by adding this amplifier to improve the resolution.

In the current or voltage measurement, the measurement is not often met AC DC but, this time, definitely not the direct input AC signal to the digital voltage meter to go, must first measured the AC signal into a DC signal, into the digital voltmeter can be measured. The figure is converted into an AC signal to DC signal reference circuit. (Note: better communication be converted into the DC circuit is a "True RMS" conversion circuit, but because of its special chip is expensive, high-end multi-application in some situations.)
  This circuit, the input is 0 ~ 200.0mV the AC signal, the output is 0 ~ 200.0mV DC signal, the signal amplitude from the point of view, does not require any amplification circuit, but it is the amplification of the circuit itself only ensure the conduct of its almost no loss of AC – DC signal conversion. So here is the use of low-power high-impedance input operational amplifier, the insensitive zone is only 2mV just about the extensive use of common digital multimeter, the circuit very much the same.

In the temperature measurement and the amount of other physical and chemical measurements, often a "zero" when the signal is not zero, and this time, the following "bridge type" circuit was first used. According to the characteristics of the signal with the sensor in the replacement of a bridge circuit with a resistor element. Digital voltmeter input is no longer of the two sites are connected, as a typical "differential" input to use.

Variant of the bridge input circuit can also be extended to the following circuit, which is a the 4 ~ 20mA current into a digital display circuit. It is the 4mA zero rather than 0mA. When the input current of 4 mA zero time, the use of IN-established above the voltage IN + offset occur because 4mA unwanted signals, making the digital voltmeter differential input = 0 to 4mA input displays to achieve the requirements of 0 . As the signal continues to increase, for example to 20mA, digital voltage meter, the equivalent differential input current is 20-4 = 16mA, 16mA the voltage drop across the resistor in the 62.5R is the largest digital voltmeter input . At this time, the digital voltage meter to the reference voltage adjustment with 16 * 62.5 = 1000mV equal, show that 1000 words!

Application Note:
  1. Digital voltage meter (digital panel meter) concrete application of the circuit is far more than do, as long as some of the most basic application of control to be giving top priority to more and more skilled, mature stude

nts can be clever, you can follow your idea to handy to make good use of it!
  2. Although the digital voltmeter input impedance of 1000 megohms, but this resistance is only in terms of the input signal, with the usual power system generally referred to as the "insulation resistance" a big difference! Therefore, do not put any more than the chip supply voltage input to the circuit! To avoid losses or dangerous!
  3. Digital voltmeter (digital panel meter) is a measurement tool, and its own direct impact on the measurement results, so all the examples above, the use of the resistance requirements can not be less than 1% accuracy in triage, partial pressure and the standard resistor chain, preferably 0.5% or 0.1% precision resistors. Capacitors used in the circuit also requires a capacitor commonly known as the CBB, in addition to areas outside the individual, generally can not use ceramic capacitors.
  4. Do not work in the circuit itself is not sent with the signal when the power supply, it is very easy to damage the chip. Cut off the power supply before the first signal must also be removed.
  5. Digital voltmeter (digital panel meter) expansion of the use and application, it must be well read the instructions provided by suppliers, do not rush to send power to use it.