Digital multimeter circuit using ICL7107

This is Digital multimeter circuit using ICL7107. We can modify the dc digital meter circuit to smart full function multimeter, that versatile available. For example : measure DC voltage, ACV, DC Amp meter, AC Amp meter and as the Ohms meter etc.

Try to build this projects to use it really worth Fully enjoy

Special Feature
DC Voltage: 200mV, 2V, 20V, 200V, 2KV, 20KV
AC Voltage: 200mV, 2V, 20V, 200V, 2KV, 20KV
DC Amp: 200uA, 2mA, 20mA, 2A, 10A
AC Amp: 200uA, 2mA, 20mA, 2A, 10A
Ohms meter: 200, 2K, 20K, 200K, 2M, 20M

DC voltage measurement

DC voltage measurement

Figure 1 DC voltage measurement

In Figure 1 the schematic diagram of this project. Of course, the easiest way is used as the DC voltage meter circuit.

The characteristics of the circuit That can measure voltages up to 200mV. We can be applied to measure the voltage range higher. As circuit is shown in table 1

the resistance at various ranges
Table 1 is shown in the resistance at various ranges.

Note: We may choose resistors in both formats. For the very high voltage measurement. It is necessary to use the external high voltage probe.

Note: R3=100K ; R4=10K

DC current measurement

Next take a look at the simple DC Ammeter circuit is Design appropriate determine the resistance in parallel with the input of the digital meter only.

The principle to calculate the resistance is The voltage caused by the flow of current across the resistor in each range is maximum up to 200mV as show in Figure 2

DC Ammeter circuit
Figure 2 DC Ammeter circuit

In Figure 2 is a circuit that is designed to have a range of up to 5 range. For the high current measurement 2 Amperes, Should the input separately, because the contact of switch that can not withstand currents.

Diode D1, D2, overload protection is provided for the input.

Note: R2= 90 ohms, R3= 9 ohms

AC voltage measurement

We can design the AC voltage measurement circuit. By add the AC to DC converter circuit that has the together relationship as show in Figure 3.

the AC voltmeter circuit
Figure 3 the AC voltmeter circuit

The AC voltage is measured to reduce voltage same the DC voltmeter circuit. Then fed to the AC to DC converter circuit by IC1 and accessories in Figure 3.

VR1 serves as a tune to the correct voltage reading.

AC current measurement

The same principle applies to the DC voltmeter circuit. We can be applied to the AC ammeter by adding the AC to DC converter before as show in Figure 4

AC current measurement
Figure 4 AC current measurement

Ohms meter
advantaged that our digital meter better the regular meter. The reading was accurate, and can also be used to measure the resistance of 0.1 ohms or less, such as high as 10M easily, by the circuit connection as shown in Figure 5.

the ohms meter circuit
Figure 5 the ohms meter circuit

the ICL7107 module
Figure 6 the ICL7107 module

The digital meter module in Figure 1-5 We have shown for the legs of the circuit ICL7107. Compared to the legs of the modules to Easy to write all the circuits. The ROH pin is the output reference voltage at middle leg of the horseshoe-shaped resistor

the full circuit diagram of digital multimeter
Figure 7 the full circuit diagram of digital multimeter

In Figure 7 is a circuit work perfectly by show PCB layout and the components as show in Figure 8, which can be used to create a user-friendly way.

the pcb layout and components layout
Figure 8 the pcb layout and components layout

Parts you will needs.
IC1____TL071__Operational Amplifiers – Op Amps JFET Input Low Noise
IC5____LM7805____Standard Regulator 5 Volt 1 Amp 3 Pin 3+ Tab TO-220
IC3____CD4049____CMOS Hex Inverting Buffer/Converter
IC2____CD4066___Quad Analog Switch/Multiplexer/Demultiplexer
IC4____ICL7107 or ICL7106____Analog to Digital Converter Single Dual Slope 0.003k SPS 3 1/2 Digit LED 40-Pin PDIP
LED 7 segment or LCD display
More Switches please read in text
Resistors tolerance: 1%
R1,R26__________________10M 0.5 watts
R2,R25,R30,R33,R36,R38___1M 0.5 watts
R3,R15,R24______________100K 0.5 watts
R4,R19,R20,R23___________10K 0.5 watts
R5,R22___________________1K 0.5 watts
R6______________________110 ohms
R7______________________1K 0.5 Watts
R8_____________________100 ohms 0.5 watts
R9_____________________10 ohms 0.5 watts
R10____________________1 ohms 1 watts
R11,R12,R13,R14_________0.1 ohms 2 watts
R16____________________3.3K 0.5 watts
R17,R27________________2.2K 0.5 watts
R21____________________100 ohms 0.5 watts
R28____________________270 ohms 0.5 watts
R29____________________47K 0.5 watts
R32____________________ 5K 0.5 watts

MKT capacitors
C14______33pF 63V
C15______330pF 63V
C16______0.0039uF 63V
C11______100pF 63V
C10______0.1uF 63V
C9______0.01uF 63V
C8______0.47uF 63V
C7______0.22uF 63V

Electrolytic capacitors
C5,C6_____470uF 16V
C13________10uF 16V


Switch see in circuit and PCB layout


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