Have you ever wanted a selfmade, opensource Voltmeter for your car ?

Please do not measure higher voltage than 12V!

With some low-cost electronic parts, you will build this in a few minutes!

Parts of this project: -> Arduino Uno or Duemilanove (available here: http://amzn.to/1CvVgqa )

-> LC Display (16x2) (available here: http://amzn.to/1IGM6rv )

-> Breadboard (available here: http://amzn.to/1a2vAqs )

-> Some jumpers ( available here: http://amzn.to/1FWjL2r )

-> A potentiometer 10k Ω ( available here: http://amzn.to/1CZLw8b )

-> 1x 10 kΩ resistor, 1x 14 kΩ resistor, 1x Z-Diode (5,1V)

-> Arduino IDE ( available here: http://arduino.cc/en/Main/Software )

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If you like this project, please vote for it! Just click on the orange vote button in the upper right hand corner and click vote! I would really appreciate it!

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## Step 1: Creating the Electrical Circuit:

First of all, we have to search for the LC Display - Datasheet on the Internet. In this case, I used this Display here:

http://bit.ly/1BSWHd9

---> Open now the Arduino IDE, click on "data", click on "samples" , click on "Liquid Crystal" and load the "Hello World" -Sketch.

Now you are able to create your electrical circuit...

After all you can prove your electrical circuit, load the "Hello World" - Sketch, the LCD should work now.

## Step 2: Modify the Existing Circuit:

Ok.. Lets go to an interesting part:

For example, if you would like to measure the voltage of your cars battery, take your arduino voltmeter:

Princip of the Circuit:

-> The measurecircuit exists of a simple voltage divider using two resistors ( 10kΩ, 14kΩ) and a Z-Diode (5,1V)

-> The Z-Diode protects the Arduino in case of overvoltage!

-> If we would like to measure the voltage up to 12V, we have to use simple maths calculation.

-> The maximum Voltage of the analog Port (A0) is 5V.

-> I made a small maths calculation. Have a look at this :D

You only have to modify the existing Circuit :D

If you created the circuit, load the following Arduino Code onto your Microcontroller.

-> Have fun with your new car battery measurement system :D

Thank you very much

<p>Hey, I Like this topic alot. I Would like to add LED to blink when voltage is getting low. Is this possible? Could somebody set me in the right direction. Thx Cheers</p>
<p>You should try and modify it to read greater than 12v. A car battery usually sits between 12.4 and 12.7 but can get almost to 14 when the car is idling and the alternator is charging the battery.</p>
hey mrandle:) ok you are right will update it as soon as I can.
<p>use for R1 20K and for R2 10K ;)</p>
<p>Yes thank you very much ! :D I know it :D:D</p><p>Now I updatet it too :D</p>
<p>make the voltage divider for 15V to 5V! the zener diode might provide some sort of protection but you'll be out of scale if you're measuring higher voltages... Don't forget about voltage spikes! </p>
<p>This is great! I love making fun things like this. </p>
<p>Thank you very much :) If you want to know, how to measure higher voltages, dont be afraid to ask me :D</p>