Simple Electronic Project

Building a Simple Electronic Project: Battery Voltage Monitor


The simple battery voltage monitor that we are going to build is made up of two light-emitting diodes (LED) indicators which, if our design goes well will turn on if the monitored voltage goes below separate threshold levels. It is applied in battery operation system where unmitigated results could arise if the battery level goes beyond a certain level. Apart from the basic LED indicators, we will be using a twine threshold design. If we have to design something simple, then we have got to make it worth the time. The threshold levels can be set slightly above the supposed critical level, making the voltage monitor to give a warning first before it goes to the critical level.


If you have experiences with building electronics projects, my best bet is that you have come across situations where the stipulated values of components that you initially designed your circuits with aren’t compatible. The truth is building circuits in real life and building it in software enabled circuit designers like Proteus is totally different. There are a lot of facts that are at play in this but the simple voltage monitor is for this project is straight forward. The circuit diagram is as shown below;

circuit diagram
Fig 1. Circuit Diagram


The basic components as shown in the circuit diagram are resistor, capacitors, LED diodes, and comparators. To get the groove on, you will also need equipment like a soldering iron, soldering brass, voltmeter and ammeter, vero board, link wires and light source. The two comparators (IC2) share a common voltage reference which is a simple shunt regulator with a resistor R4 serving as the load resistor and diode IC1 as the voltage stabilizer. The other details are probably too complex, so let’s just go straight to the building. However, as you know, you have to go to the nearest component market to get these things as they cost peanuts. Since these components are cheap, you can buy at a double, just in case in the process of testing, a component gets fried.


The construction of the battery voltage monitor is extremely simple, thus anyone can built it. The vero board is the number most important component for construction. For this project, the size of our vero board will be cut according to desired size using a mini hacksaw.

Construction and Assembling of Components
Fig 2. Construction and Assembling of Components

The final work can be built and assembled into a plastic or metal box. It is connected to the mains using a twin lead cable but in most cases, it is most likely incorporated into another project. Either way, the LEDs and the circuit board can be dealt with in two different ways. One of these ways is the mounting of the board is mounted on the case, and then it is hard wired to the LEDs which are at the front panel. The other way is the mounting of the circuit board on the plastic case on which the LEDs are then mounted onto the holders on the front panel of the case. It is however better to use the second method as it works well with any LED holders of great quality. If the LEDs are not mounted on the circuit board however, they can be fitted in a single-sided solder pins on the board.

Make sure that the LEDs and the comparators are connected with the right polarity and ensure that to brush the contact surfaces before soldering.


If you have a variable voltage supply, connect the output terminals of the circuit to the input terminals of the voltage monitor circuit. Try to vary the voltage within the threshold levels. When the supply is slightly above the threshold level, the two LEDs will remain off. But reducing the voltage below these levels will result in the LEDs switching on.

For high critical values, you can fine tune the thresholds by simply increasing the values of the resistors R1 and R6. And if you want a lower threshold, you will have to reduce the resistance value of R1 and R6. But have it in mind that the required resistance should and must have at most 1% tolerant to get efficient accuracy. In the absence of a variable suitable, you can test the voltage monitor using what it was initially made for; using batteries.

Use a batter or connect two or more batteries in series in order to get a supply potential that is higher than the two thresholds of the circuit. Once you get you get the threshold, you can then remove batteries to reduce the voltage supply which should switch the LEDs on.

While testing, always take precautions. If there is any sign of a malfunction, make sure you disconnect the supply immediately, and then recheck the circuit connections for errors. Make sure that your built monitor is connected with the right polarity setting, else the semiconductor components and capacitors could be damaged.