You’ll note from the link above that there are actually multiple parameters you can give to analogReference, however not all microcontrollers support them: This command lets the Arduino know that it should use the external reference on the AREF pin instead of the supply voltage. In order to use the external reference in your code, you need to specify it using the analogReference command. This reference voltage cannot exceed 5-volts. The Arduino Uno is also capable of using an external voltage reference, which is connected to the AREF pin. But that variance can affect the accuracy of the analog to digital converter when it’s used as a reference. When using the linear regulator with an external supply the accuracy is determined by that regulator, which can also vary from exactly 5-volts.Īs long as the voltage is between 4.75 and 5.25 volts the Arduino logic circuitry will be happy. These voltages are not always precise, the USB voltage is dependent upon your computer’s power supply and the length and gauge of the USB cable itself. This is supposed to be 5-volts and can be derived either from its USB port or from its internal linear voltage regulator, which is used when the Uno is powered using the barrel connector. Voltage ReferencesĪs stated earlier one of the factors that determine the accuracy of our ADC is its reference voltage.īy default, the Arduino Uno uses its power supply voltage as the reference. It consists of a 7.5k resistor and a 30k resistor. I’ll be using one of these dividers in our experiments. These devices are extremely inexpensive and use precision resistors to give an accurate reading. However, If you are planning on using your Arduino to measure lower voltages, less than 26-volts, you can purchase a premade divide that will do the job. You can certainly construct a voltage divider using discrete resistors, in fact, if you are planning to measure very high voltages then you’ll probably have to.
This reduces the voltage and has the added benefit of increasing the input impedance, which means that the measurement device won’t load down the circuit it is trying to measure and distort the reading.
To accomplish this we can use a voltage divider, a very simple circuit constructed using two resistors. Obviously, this is a bit impractical, as you’ll probably want to measure input voltages exceeding that. The maximum input voltage that you can feed into an Arduino Uno ADC is 5-volts, with microcontrollers using 3.3-volt logic it is even less. With the ESP32 and Seeeduino XIAO, we have a selection of 12-bit ADCs, allowing them to resolve the input voltage down to 4096 steps. Other microcontrollers also have built-in ADCs, some of them with a greater resolution than the Arduino Uno. The Uno has six 10-bit ADCs, meaning that they can resolve the input down to 1024 discrete steps (2 to the power of 10 equals 1024). Many microcontrollers, like the Arduino Uno, have built-in ADCs. Linearity – The converter needs to have a linear output, that is to say, it needs to have its output readings increase by the same amount for each increment. This also determines the maximum voltage the ADC can accept at its input. Voltage Reference – The converter is only as precise as the reference voltage applied to it. The more boots, the more granular the output can be. Number of Bits – This determines how many “steps” the converter can divide the input into. The accuracy of this conversion is determined by a few different factors: It’s a component that accepts an analog input and produces a digital output, the output being a digital representation of the level of the input. Analog to Digital ConvertersĪn Analog to Digital Converter is pretty well exactly what it sounds like. Many modern microcontrollers, including the Arduino Uno, have a built-in ADC, making DC voltage measurement the simplest of our four tasks. Measuring DC Voltage with a microcontroller (or any digital data device) requires the use of an Analog to Digital Converter (ADC).
The techniques here apply to any microcontroller, in fact devices like the ESP-32 or Seeeduino XIAO can actually perform better DC voltage measurements as they have analog to digital converters with a higher resolution.
VIN TO PIN CALCULATOR HOW TO
In this article, I will show you how to measure DC voltage and current using an Arduino.
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