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    Here is an interesting Car Battery Monitor circuit of a low power electronic dc voltmeter circuit that can be used with car electric systems that run on 12 volt batteries. The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries.

    At the heart of the circuit is a ubiquitous dot-bar volt meter LM3914N (IC1). This IC is operated in the expanded-scale mode so that the circuit responds in the 10-16V range. IC1 outputs a steady voltage on pin 7 from the internal voltage reference. This is fed via voltage dividers VR2and R2 to the internal reference input pins(4&8) to set the range that the meter is sensitive to. The measured voltage is fed in on pin 5 via the voltage divider consisting of R1 and VR1. This divider scales the input voltage down to a range that is useful to IC1.

    Car Battery Monitor schematic for 12V batteries

    car battery monitor diagram

    suggested front panel of the car battery monitor

    It is possible to set the meter to read equal steps across a variety of upper and lower voltages. Different colored LEDs can be used for the voltage level indicators(D1-D10). It will be necessary to have an adjustable regulated DC lab power supply and a good quality digital volt meter (DVM) to perform the calibration. Connect the external volt meter across pins 6 and 4 of IC1 and adjust VR2 for a reading of 1.2 volts. Center the settings of VR1 and VR3. If the span between the end points of VR1 is 4.5V, the circuit is ready to use as a 10.5 to 15V scale battery monitor.

    Adjust the lab power supply from 9V to 15V and check where the meter is reading, it may not read at all until the potentiometers are near the right range. In this case, set the lab power supply to 12V and adjust VR3 until one of the green LEDs (D4-D7) light. Adjust the power supply until the first LED just comes on, measure that voltage. Adjust the supply up until the last LED just comes on, measure that voltage and subtract the first voltage, this is the span. Adjust VR1 and repeat the previous adjustment until the span is 4.5V. Now set the voltage to 10.5V and adjust VR3 until the lowest LED (D1) just turns on. Note that VR1 and VR3 interact so it may be necessary to perform the adjustments a few times to get it right.

    After construction and calibration, fit the voltmeter unit in the dashboard and connect input leads across the 12 Volt vehicle battery terminals, with correct polarity. Now watch the LED display panel for a battery level indication. If the voltage is higher than the top step, the highest LED (D10) will remain on. If the voltage is lower than the bottom step, all of the LEDs will stay off.


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    12 Responses to "12V Car Battery Monitor"

    1. on the schematic vr2 is showing 200e is it 200 ohm or 200 k

    2. Hello, great simple approach. However, R1 is blurry showing the value. For clarity, please verify the value. is it 40 ohms or 4k7 is what i think i see and if so, please explain this value. thanks for your time.

    3. Hi
      Can you tell me what watt the resistors should be
      Thank you

    4. sir,how can i use the circuit to 24v

    5. very interesting,applicable to any of my future project.

    6. Very good article. Have one question tho…
      You state that original adjustments should be made, then later say “Adjust the lab power supply from 9V to 15V”
      Does that mean the original adjustments should have been made at 9V?
      Thank you.

    7. Thanks! The procedure of the “one-time calibration” is described in the second paragraph:

      “Adjust the lab power supply from 9V to 15V and check where the meter is reading, it may not read at all until the potentiometers are near the right range. In this case, set the lab power supply to 12V and adjust VR3 until one of the green LEDs (D4-D7) light. Adjust the power supply until the first LED just comes on, measure that voltage. Adjust the supply up until the last LED just comes on, measure that voltage and subtract the first voltage, this is the span. Adjust VR1 and repeat the previous adjustment until the span is 4.5V. Now set the voltage to 10.5V and adjust VR3 until the lowest LED (D1) just turns on. Note that VR1 and VR3 interact so it may be necessary to perform the adjustments a few times to get it right”.

      Note that you do not need a lab power supply,after this calibration.

    8. Hello!!I’m so glad that you had made a comment in my blog, Genetic Argonaut. Now, anenirswg your questions:1 What kind of ES did you used?! (a,b) or (a+b)? My ES is configured by this way: Parents Population = 60 Offspring Population = 60 Total of Generations = 5000 Kind of ES = (a+b)ES, because each parent generates one offspring and the selection occurs in the population formed by the parents + offspring. 2 Didn’t you turn the mutation off to see if you find a the optimum? I made the Gaussian Mutation with some modifications. Those modifications allows the ES to work better inside the variables’ intervals. With those modifications the ES can (or cannot) escape from a place that is a local optimum. But I need to make more simulations to verify the mutation operator’s behaviour.3 And another unrelated point do you apply evolutionary methods on some real-world application? So far I did not do this, because my advisor is finishing his Phd and before I had studied Neural Networks. I started with EC around one year ago, but when my advisor come back next August, he and me will use EC to evolve Neural Networks in weather forecasting. I’m an Undergraduate student interested in Artificial Intelligence. I hope that I had answered your questions. I’m very glad that you had asked them. But, now, let me ask you some questions: What problems did you face using EC ? Did you try the DeJong Test Suit with your EC algorithms ? See You!! Marcelo (a.k.a Nosophorus)

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