Voltmeter circuit using LED

admin November 7, 2018 19 Comments

Car Battery Voltmeter Circuit

Description

The main onjective of the car batter voltmeter circuit using LED is to work as a warning inducator using a voltmeter circuit to test the life of car batteries. A voltmeter, though can be bought from a store, is designed as a circuit to make the whole arrangement a lot more interesting. A voltmeter is basically a testing device that is used to measure the potential difference between two points of either AC or DC form. Here the voltage is measured by associating the voltmeter with the charge left in the battery.

The voltmeter circuit is connected across the battery terminals. That is, the battery voltage is given to the inverting inputs of the IC. The indicated voltage on the voltmeter is compared with the reference voltage which is processed on the zener diode D1. The zener diode works like a usual diode and allows the current to flow in one direction, but also has a characteristic of current flow in the opposite direction if the voltage is more than its breakdown voltage. This obtained value is adequate to supply good thermal stability.

A 10K POT is also connected to change the voltage levels to output in the form of glowing LED’s. The output LED indicators must show car battery voltage with an interval step of 1 Volt (11V, 12V, 13V & 14V).

This is a very useful circuit which when installed on your car gives the voltage of you car battery in a LED dot display form. The circuit is based on four comparators made of quad op amp LM324. The inverting inputs of IC are kept at at reference voltages 5.6V, 5.2V, 4.8V, 4.4V respectively at pins 2, 6, 9, 13 by resistors R3, R4, R5, R6. The battery voltage is directly fed to the pin inverting input through the voltage divider arrangement using R1 and R7. When there is a variation in the input supply the output of each op amp goes high accordingly as they are wired as voltage comparators. Thus the corresponding LED glows.

If a car battery indicates an output voltage of 12 Volts or more, using the voltmeter circuit, it means that the battery has a good life. If the battery voltage goes below 12 Volts and up to 11.6 Volts, it indicates that the battery has started discharging. If the battery voltage goes even lower there are only two possibilities. Either the battery is failing or it is low in water.

NOTE:

It is always advisable to measure the battery charge at “high current” instance. This can be obtained by turning ON the head lamp in high beam mode. While checking the output voltage at this condition, if it shows a steep drop, better change the battery soon.

Voltmeter Circuit Diagram and Parts List

Car Battery Voltmeter Circuit Using LED

Car Battery Voltmeter Circuit Using LED

ComponentSpecification
ICLM324
R115K
R21.2K
R3, R4, R5680 Ohms
R610K POT
R710K
R8 to R111K
D15.6V / 0.5 Watts Zener Diode
D2 to D5LED

Notes

  • IC LM 324 consists of 4 op amps in one package, so power supply is common and is shown once (pin 4 and 11).
  • To setup, connect  the circuit to battery, adjust R6 so that required voltages are available at the inverting pins (refer description to get the required voltages).
  • Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit diagram. The gadget is now ready.

Our website has more related circuits that you may like to read, Take a look:

1. 24 Volt Battery Charger Circuit

2. Battery Eliminator Circuit

3. Car Battery Charger

4. Battery Charging Indicator Circuit

5. Automatic Changeover Circuit

Comments
  • Ariharan T
    April 18, 2017

    But a car battery delivers high current right?. Are u using 1/4 W resistor in this circuit ?

  • lrfc
    May 15, 2015

    i have made this circuit and it works but all 4 leds light at a time please can any one tell me what should be the status of leds on varying voltage .i have used simple 9v battery for it..

    • Nick
      November 4, 2016

      Check orientation of 5.6v zener.
      This circuit is powered by the battery ( cars 12v battery ) that it is showing status of. No need for 9v battery

      10k ohm pot, R6, should be set to 7480 ohms.

  • March 30, 2015

    Thanks! is a very easy circuit usint also one IC.

  • Matthew
    August 15, 2012

    For your Car Battery Voltmeter Circuit, would you be able to tell me what resistor values I would need to monitor a 6 V supply? I am looking to build a circuit to visually indicate whether a device is receiving 5.7V-6.3V (Indicating all is well), 3V-5.69V(Might be a short) or Below 3V(basically dead).
    Thanks In advance,
    Matt Bragg

    • Charles Tomlinson
      August 20, 2018

      Hi Matt, I am not sure exactly what you require but if you change the zener to a lower value, say 2.8v this mite be a good place to start experimemting for you.
      Good luck
      Chas.

  • Destate9
    May 20, 2012

    First of all, it seems unnecessary to use two pins of the pot (R6). Second of all, I understand this circuit must work for you, however, why did you choose for the LEDs to be powered with the unregulated voltage of your car battery when it can sweep from 11-14 volts? Also, R8-R11 are pretty large for your typical LED resistor. Your probably getting 9-12 mA per LED when they can take up to 20 mA

  • anıl
    May 13, 2011

    selamın aleyküm

  • Conrad
    March 1, 2010

    Super good!

  • […] that V_i=i/N * V_ref for equal resistors. I am currently looking into that, and the diagram here: here. I need the voltages to be 12.6 12.5 12.4 12.24 12.12 12.00 11.9 11.8 volts, so there is a slight […]

  • Munawar
    January 15, 2010

    I am very found to take intrest in Electronic. if you have funny circets then tell me. send me its Digrams
    on my email Adress: computerlinksjhang@yahoo.com .

  • jinesh
    January 13, 2010

    excellent circuit,i am serching for this circuit for a long time..thanks

  • prasanna
    December 29, 2009

    circuit was quite interesting……..

  • Romeo
    November 19, 2009

    How would you change this circuit for voltages less than 4? I teach grade 9 students and a project is a wind turbine. This would be great for them to see some yellow, red and green LEDs

  • August 18, 2009

    tkanks good circuit which i was looking since long.pl keep sending such good circuits for my wv 1958 model .

  • August 18, 2009

    Что-то я почти ничего не понял..

    • admin
      August 18, 2009

      какая часть вам наклоняю понимаю.
      пожалуйста, сообщите мне.
      Я помогу тебе

  • fethi
    June 27, 2009

    salut j ai réalise montage car batterie voltmètre
    les quatre led allumé sur une tension 10 v

  • todd
    December 17, 2008

    I need to build a stop watch display on a lcd or 7 seg to add to my efx-tex prop-xs micro controller!!!this looks like this mite be what I need!!! Can you tell me how to build this!!!

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