Voltage Level Indicator Circuit Using op-amp, Simulation in Proteus

LED voltage level indicator circuit using an operational amplifier (Op-Amp)

Previously, I have made a tutorial on how to simulate voltage level indicator circuit using the LM3914 Dot/Bar graph Driver. The LM3914 is a monolithic analog controlled LED driver IC as well as its counterpart the LM3916, the difference between the both is that the LM3916 gives a logarithmic output scale, while the LM3914 gives a linear output scale, this makes the LM3916 suitable for volume unit (VU) meter. The IC can drive 10+ LEDs. One interesting thing about the IC is that it can be configured into either a dot output mode or a bar graph output mode.

In this tutorial, you will learn how to design LED voltage level indicator circuit using an operational amplifier (op-amp), and be able to carry out circuit simulation of the same voltage level indicator circuit in Proteus. You will also be able to download the circuit of the Proteus simulation file of the LED voltage level indicator circuit.

What is Voltage Level Indicator Circuit?

A voltage level indicator circuit is a circuit that is designed with the purpose of indicating the level of voltage in a device in which it is appropriately connected. Because the electronic component used to show or indicate the level of voltage measured is a light emitting diode, the circuit is often called an LED voltage level indicator. This circuit is found in various devices where voltage indication is necessary. We can find this circuit in any electronic device that runs on batteries. The circuit tells the user of such a device the level of the battery life, which is indicated using LEDs. in order to tell the user of such a device the level of device’s battery life, the voltage level indicator circuit measures the level of battery voltage and displays it through an LED. 

The device is designed such that an LED is made to come ON beyond a certain voltage level. I.e. The circuit is made such that if for instance the reference voltage is 3 volts, then, once the voltage goes beyond 3 volts, an LED comes ON. Therefore, if we have such a circuit set up for 3 volts, 6 volts, 9 volts and 12 volts. We can arrange the LEDs on a single line in the order the LEDs come ON, so, the LED for 3 volts comes ON first followed by the LED for 6 volts, then 9 volts and 12 volts. This way, we can have a bar graph that indicates the level of voltages in a battery. And when the battery voltage level starts going down, the LEDs will start going OFF sequentially. This way we can monitor the level of the battery voltage.

How to Design the LED Voltage Level Indicator Circuit?

There are four stages to making an LED voltage level indicator 

  • Stage 1: Voltage divider circuit design
  • Stage 2: Voltage comparator circuit design
  • Stage 3: Voltage level indicator design

Stage 1: Voltage divider circuit

So, let’s say it is a battery that can charge up to 12 volts that we want to measure, and indicate its voltage level with respect to 3 volts, 6 volts, 9 volts and 12 volts. We have to design a circuit that can divide a voltage source equally into 4 parts (3, 6, 9, 12). With such a circuit, a 12 volts source will be divided to obtain 3 volts, 6 volts, 9 volts and 12 volts. To make such a circuit, we bring in our knowledge of circuit divider using resistors. A resistor can do the job perfectly. With the right number of resistors, we can make a voltage divider circuit of our choice. See image illustration below

voltage divider for operational amplifier
figure 1 voltage divider for operational amplifier

To divide a given voltage value into various parts, we use the voltage divider formula to realize that.

The voltage divider formula is shown below:

VR1 = [R1/(R1 + R2 + R3 + R4)]V

  • V = Voltage to be divided
  • VR1 = Voltage drop on resistor R1
  • R1 = Resistor R1
  • R2 = Resistor R2
  • R3 = Resistor R3
  • R4 = Resistor R4

This is the formula to find out the voltage that will drop on the resistor R1, putting into consideration the other resistors R2, R3, and R4. 

This way also we will find the voltage drop on the other resistors.

From the voltage divider we have above, the resistors are of the same value 100𝛀. This means that the voltage will be divided into four equal parts of 3 volts each. So if we want to get 6 volts, we add two 3 volts, and for 9 volts, we add three 3 volts, then for 12 volts we add four 3 volts. 

When you look at the image illustration above, you will see that the DC multimeter is connected to the resistors in such a way that we can measure 3 volts, 6 volts, 9 volts and 12 volts.

Stage 2: Voltage comparator circuit design

Here, we use an electronic component that has the ability to take in two different voltages. One voltage will serve as a reference voltage, while the other voltage will be the varying voltage. The voltages we obtained from the voltage divider will serve as the reference voltages, while the external voltage to be measured will serve as the varying voltage. Sometimes the external voltage source to be measured will provide the reference voltage source, it all depends on what you want to design in your electronic circuit.

To understand how the voltage comparison works, we need to learn how that very component that compares two voltages works. The electronic component that does that is the “Operational Amplifier” abbreviated as “Op-Amp” . The Operational amplifier has the ability to take in two voltages from its two input points. Depending on what you are designing, the operational amplifier can do a lot of things in electronic circuit design. It can be used to design an amplifier, it can be used to design an oscillator, it can be used to design a filter, it can be used to design a comparator and so many other circuits. In this project, we are using it to design a comparator. Though there are some electronic components specifically designed as comparators, however, the operational amplifier which is cheap and easy to use can perfectly serve as a comparator.

How an operational amplifier works

I am creating a content on operational amplifiers, the tutorial will teach nearly everything you need to know to use an operational amplifier, however, in this very tutorial, we will look at an operational amplifier as a comparator. Below is the circuit symbol of an operational amplifier.

operational amplifier symbol
figure 2 Operational amplifier symbol

The image above is the circuit symbol of an operational amplifier. It has two input terminals, the inverting input and the non-inverting input. It also has two supply voltages, the positive supply voltage and the negative supply voltage. Then it has the output voltage.

  • V+ = Non-inverting input
  • V- = Inverting input
  • Vs+ = Positive supply voltage
  • Vs- =  Negative supply voltage
  • Vout = Output

How the Operational Amplifier Works as a Comparator

In a nutshell this is how an operational amplifier works as a comparator. If you connect Vs+ to a positive voltage, say 12 volts. And you connect Vs- to ground. Then, if you connect say 3 volts to V- and a varying voltage to V+, as you vary the voltage entering V+, as long as the 3 volts connected to V- is greater than the varying voltage at V+, the output will be giving out 0 Volts  which is the voltage value connected at Vs-, but once the varying voltage at V+ goes beyond 3 volts, the output will start to give out a voltage that is nearly equivalent to the voltage connected to Vs+, (Vs+ minus 1.5 V =  12 – 1.5 =  10.5 V). 

Note that in this situation, the 3 volts connected to V- is the reference voltage. Hence, we can have the 3 volts, 6 volts, 9 volts and 12 volts as references, while the voltage on the V+ serves as the varying voltage being measured. So, we can have four comparators for four voltage comparisons, so as to measure four voltage levels and give out four outputs which will turn ON four LEDs. 

See image illustrations below:

voltage level indicator
figure 3 voltage level indicator with LED off
Voltage level indicator
figure 4 Voltage level indicator with LED on

In figure 3 above, the varying voltage to be measured is below 3 volts, hence the output is 0 volts and the LED did not come ON. But in figure 4, the varying voltage to be measured is above 3 volts, this causes the op-amp to output voltage that saturates towards Vs+, which has a value Vs+ minus 1.5 volts. This output voltage is then used to light up the LED as shown in figure 4 above.

Stage 3: Voltage Level Indicator Design

After the voltage comparator circuit, the next circuit in the voltage level indicator circuit with Op-amp is the LED circuit. The LED circuit is already shown in figure 3 and 4 above. Once the varying voltage has gone just beyond the reference voltage of either 3v, 6v, 9v and 12v, the LEDs connected to the four operational amplifiers used in the circuit will come ON. 

The circuit diagram for the complete circuit is shown below:

voltage level indicator complete circuit
figure 5 voltage level indicator complete circuit

Proteus Simulation of the LED Voltage Level Indicator Using the Operational Amplifier

To have a better appreciation of this design, you can start with the simulation. You can simulate this circuit in Proteus circuit simulation software. To do that, you can download various versions of the Proteus simulation software with the download link given below, install the software and carry out the simulation on your computer.

What is Proteus simulation software?

According to Wikipedia, The Proteus Design Suite is a proprietary software tool suite used primarily for electronic design automation. The software is used mainly by electronic design engineers and technicians to create schematics and electronic prints for manufacturing printed circuit boards.

It was developed in Yorkshire, England by Labcenter Electronics Ltd and is available in English, French, Spanish and Chinese languages.

There are various versions of the Proteus simulation software on the market, but the latest version at the moment of creating this tutorial is Proteus version 8.14. You can use the link below to check out the various versions  I have and make a choice. If you are finding it difficult to choose a version, reach out to us through email. We can help you choose. You can download Proteus 8, Proteus 8.9, Proteus 8.10, Proteus 8.11, Proteus 8.12, Proteus 8.13.

After downloading the circuit simulation software. and installing the software, use the simulation file download button below to download the Proteus simulation file of the LED voltage level indicator, then run the simulation on your computer and see how the circuit behaves. 

In the circuit, as you vary the external voltage to be measured from 0 volts up, before the varying voltage gets to 3 volts, all the LEDs will be OFF, but one the varying voltage has gone beyond 3 volts, the first LED will come ON, the second LED will come ON once the varying voltage goes 6 volts, then 9 volts and 12 volts. With these LED indicators, we can tell when the voltage of the external power source to be measured is either 3 volts, 6 volts, 9 volts or 12 volts. 


As the voltage of the measured source starts going down from 12 volts, the LEDs will start going OFF until the voltage has gone below 3 volts, then all the LEDs will go OFF.

This is how to design an LED voltage level indicator using an operational amplifier. You can carry out the real design yourself. You can get the components used easily in the market.There are various types of operational amplifiers in the market, but the most common is the 741 Op-amp. However, you can use four 741 Op-amp or the quad-Op-amp like the LM324 op-Amp, which has four operational amplifiers, other components are easy to come by, i.e. the resistors, battery and potentiometer, then you can use your multimeter to measure the voltages.

I hope you have learnt a lot from this tutorial, let me know your questions in the comment section. The video for this comes soon, so you can understand better.


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