Digital voltmeter using ICL7107

The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high.

The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage under measurement. In simple words, the input voltage is compared to an internal reference voltage and the result is converted in a digital format.

The resistor R2 and C1 are used to set the frequency of IC’s internal clock. Capacitor C2 neutralizes the fluctuations in the internal reference voltage and increases the stability of the display.R4 controls the range of the voltmeter. Right most three displays are connected so that they can display all digits. The left most display is so connected that it can display only “1” and “-“.The pin5(representing the dot) is connected to ground only for the third display and its position needs to be changed when you change the range of the volt meter by altering R4. (R4=1.2K gives 0-20V range, R4=12K gives 0-200V range ).
Circuit diagram.

Notes.

    Assemble the circuit on a good quality PCB.
    The circuit can be powered from a +/_5V dual supply.
    For calibration, power up the circuit and short the input terminals. Then adjust R6 so that the display reads 0V.
    The ICL7107 is a CMOS device and it is very sensitive to static electricity. So avoid touching the IC pins with your bare hands.
    The seven segment displays must by common anode type.
    I assembled this circuit few years back and it is still working fine.

The digital voltmeter ICL7107CPL

Here is my lovingly-crafted schematic for the voltmeter module. Note that this could be made as a standalone voltmeter, it will measure up to 20v DC. In our finished product, the +5V will be sourced from an LM78L05 voltage regulator.

And the parts list:

    IC1 – Intersil ICL7107CPLZ
    IC2 – Intersil ICL7660
    D1~D3 – 1N4148 diodes
    LED displays – Agilent HDSP521G 2 x 7-segment green displays (common anode). You can use anything really, as long as it is common anode, and each segment is ~8mA
    R1 – 220 ohm – all resistors 0.25W
    R2 – 10k ohm
    R3 – 1M ohm
    R4 – 47k ohm
    R5 – 15k ohm
    R6 – 100k ohm
    R7 – 1k ohm multiturn potentiometer/trimpot (for calibration)
    C1 – 10nF – all capacitors must be rated for at least 25V
    C2 – 20nF
    C3 – 470 nF
    C4 – 100 nF
    C5 – 100 pF
    C6,7 – 10 uF electrolytic

Please note that this is a work in progress and errors may have been made, or values altered at any time after publication.

An integrated circuit MAX232

The MAX232 is an integrated circuit, first created by Maxim Integrated Products, that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals.

The drivers provide RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does not need to be made more complicated just for driving the RS-232 in this case.

The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V.

The later MAX232A is backwards compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF capacitors used with the original device.

The newer MAX3232 is also backwards compatible, but operates at a broader voltage range, from 3 to 5.5 V. 

Pin to pin compatible: ICL232, ST232, ADM232, HIN232.

LM386 based stereo audio amplifier with digital volume control

Due to its simplicity (requires minimum external components) and high availability, LM386 is very popular among hobbyists for use in low-voltage audio amplification applications. Most of the time a potentiometer is used at the input side of LM386 to provide a volume control in the output speaker. The potentiometer does not control the gain of the amplifier itself, but it creates a voltage divider network at the input, which in fact controls the fraction of the audio signal that is fed to the amplifier. This project is about a stereo audio amplifier using two LM386 ICs with digital volume control for both left and right speakers. So, how would you control the volume digitally?

You are right, by replacing the traditional electro-mechanical form of potentiometers with digital potentiometer chips. This project uses MAXIM’s DS1868 dual digital potentiometer chip and a PIC microcontroller to control the volume of a stereo output from two LM386 ICs.

Digital voltmeter using ICL7107

The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high.

 The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage under measurement. In simple words, the input voltage is compared to an internal reference voltage and the result is converted in a digital format.