The objective of this project is a build a voltmeter that can measure voltages between 0 and 30V. I will use the analog inputs of an Arduino to measure the voltage, via a voltage divider. When an Arduino is powered from a 5V supply the maximum voltage that could be measured is 5V. However, by using a voltage divider this can be increased because the resistors will decrease the voltage to that which can be measure by the analog inputs.
To understand this concept, I want to show you how voltage dividers work. Essentially a voltage divider takes a voltage and splits it into a smaller one. The diagram shows a voltage applied across two resistors that are in series. A smaller voltage has been taken from Vout and GND. Vout = Vin x R2 / R1 + R2. This equation states that the output voltage (Vout) is directly proportional to the input voltage (Vin) and the ratio of the resistors (R1 and R2).
Some important points to take from this is that if R1 and R2 are equal, then Vout will be half of Vin. If R1 is a lot bigger than R2, then Vout will be small (much less than Vin). If R1 is a lot smaller than R2, then Vout will be large (closer to Vin).
In the voltmeter, the power that will be applied to Vin will come from the voltage that is being measured. This way the Arduino will be supplied with a fraction of Vin and will be within the safe limits of the GPIO pins.
A potentiometer can be used to fine-tune the voltage.
One way that this could be improved is by adding an LCD screen, which will give a nice way of being able to read the results and also make it portable!