{"id":7635,"date":"2021-01-23T11:41:32","date_gmt":"2021-01-23T16:41:32","guid":{"rendered":"https:\/\/dronebotworkshop.com\/?p=7635"},"modified":"2023-04-12T09:27:53","modified_gmt":"2023-04-12T13:27:53","slug":"dc-volt-current","status":"publish","type":"post","link":"https:\/\/dronebotworkshop.com\/dc-volt-current\/","title":{"rendered":"Measure DC Voltage and Current with an Arduino"},"content":{"rendered":"\n

\"Download \"Parts<\/a> \"View<\/a> \"Download<\/a><\/p>\n

Part 1 – Direct Current<\/h1>\n

In the first part of our look at measuring voltage and current with microcontrollers, we will see how to measure DC voltage and current using an Arduino.<\/p>\n

In part two we will do the same thing with AC, but today our focus is on Direct Current.<\/p>\n

Introduction<\/h2>\n

There are many reasons why you might want to use a microcontroller to measure DC voltage and current. You might be monitoring the output of a generator or solar array, you could be measuring the current consumption of your project or you might want to observe the charging and discharging of a battery.<\/p>\n

<\/div>\n

In this article, I will show you how to measure DC voltage and current using an Arduino. 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.<\/p>\n

\"Measuring<\/p>\n

Let\u2019s get started!<\/p>\n

Measuring DC Voltage<\/h2>\n

Measuring DC Voltage with a microcontroller (or any digital data device) requires the use of an Analog to Digital Converter (ADC). Many modern microcontrollers, including the Arduino Uno, have a built-in ADC, making DC voltage measurement the simplest of our four tasks.<\/p>\n

Analog to Digital Converters<\/h3>\n

An Analog to Digital Converter is pretty well exactly what it sounds like. It\u2019s a component that accepts an analog input and produces a digital output, the output being a digital representation of the level of the input.<\/p>\n

\"Analog<\/p>\n

The accuracy of this conversion is determined by a few different factors:<\/p>\n

Number of Bits<\/b> – This determines how many \u201csteps\u201d the converter can divide the input into. The more boots, the more granular the output can be.<\/p>\n

\"ADC<\/p>\n

Voltage Reference <\/b>– The converter is only as precise as the reference voltage applied to it. This also determines the maximum voltage the ADC can accept at its input.<\/p>\n

\"ADC<\/p>\n

Linearity<\/b> – 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.<\/p>\n

Many microcontrollers, like the Arduino Uno, have built-in ADCs. 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).<\/p>\n

Other microcontrollers also have built-in ADCs, some of them with a greater resolution than the Arduino Uno. 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.<\/p>\n

\"Microcontroller<\/p>\n

Voltage Dividers<\/h3>\n

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. Obviously, this is a bit impractical, as you’ll probably want to measure input voltages exceeding that.<\/p>\n

\"Voltage<\/p>\n

To accomplish this we can use a voltage divider, a very simple circuit constructed using two resistors. 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.<\/p>\n

\"Voltage<\/p>\n

You can certainly construct a voltage divider using discrete resistors, in fact, if you are planning to measure very high voltages then you\u2019ll probably have to. 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. These devices are extremely inexpensive and use precision resistors to give an accurate reading.<\/p>\n

I\u2019ll be using one of these dividers in our experiments. It consists of a 7.5k resistor and a 30k resistor.<\/p>\n

Voltage References<\/h3>\n

As stated earlier one of the factors that determine the accuracy of our ADC is its reference voltage.<\/p>\n

By default, the Arduino Uno uses its power supply voltage as the reference. 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.<\/p>\n

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. When using the linear regulator with an external supply the accuracy is determined by that regulator,, which can also vary from exactly 5-volts.<\/p>\n

As long as the voltage is between 4.75 and 5.25 volts the Arduino logic circuitry will be happy. But that variance can affect the accuracy of the analog to digital converter when it’s used as a reference.<\/p>\n

\"Arduino<\/p>\n

The Arduino Uno is also capable of using an external voltage reference, which is connected to the AREF pin. This reference voltage cannot exceed 5-volts.<\/p>\n

In order to use the external reference in your code, you need to specify it using the analogReference<\/i><\/a> command. This command lets the Arduino know that it should use the external reference on the AREF pin instead of the supply voltage.<\/p>\n

You’ll note from the link above that there are actually multiple parameters you can give to analogReference, however not all microcontrollers support them:<\/p>\n