How much current does an arduino uno draw

How much current does an arduino uno draw

There is something magical about turning on an Arduino. I didn't realize it when I first started using them, but the Arduino has built-in regulation. This allows you to extend the power supply wiring by using a voltage higher than the nominal 5V or 3.3V needed for the logic level of the microcontroller (MCU). Some Arduino's accept input voltages from 6Vdc to 16Vdc, which is well above the MCU's maximum capability, but the Arduino board precisely regulates the supply voltage as well as additional power for the Arduino peripherals. I have seen experienced engineers confused about what it means to run the Arduino at 3.3V on 9Vdc until someone explains it to them.

Microcontroller power requirements

Choosing the right power supply for a microcontroller-based project is often overlooked. While the most effort and forethought can be put into the details of the design itself, many performance and reliability issues stem from the choice of power supply options and connections. the Arduino family of development boards offers solutions to these problems, but it is easy to get confused if you are not well informed about the options available during development. It is not so simple to say that Arduino 5V uses a 5V DC power supply and Arduino 3.3V uses a 3.3V DC power supply.

Arduino power requirements

Many Arduinos use the ATmega328P microcontroller. Microchip's ATmega328 has a very wide range of acceptable DC voltages. (The DC voltage is the regulated DC supply voltage required for IC operation and is often referred to as the IC supply voltage.) Arduinos are typically designed to operate with 3.3V logic for low power consumption, or 5V logic to be compatible with older TTL logic devices. The examples below are for 3.3V DC devices, where power is more important. However, the same principles apply to 5V DC devices.

Figure 1: Arduino board specifications.

Example: Arduino Pro Mini

Let's start by designing a circuit using, for example, the Arduino Pro Mini. the maximum current draw of the Arduino is 200 mA. the Arduino itself is unlikely to draw 200 mA, but let's assume that the Arduino and other connected devices draw a total of 200 mA. the ATmega328p data sheet states that a logic high on a pin The minimum voltage for a logic high level on a pin is 90% Vdc. Therefore, if Vdc is 3.3Vdc, the minimum voltage on the pin that is considered a logic high is 0.9*3.3Vdc = 2.97Vdc. Any value below 2.97V on a digital pin is in the undefined range and will lead to unpredictable results for the Arduino.

There is always a certain distance between the power supply and the Arduino. The greater the distance, the greater the voltage loss on the power line. But how much is lost? Since 26 gauge wire is a common choice for low power circuit wiring and is at the smaller end of the range of wire cross-sections, there is less copper. Less copper means less cost. Twisted pair 26 AWG is a good choice because it can be laid flexibly. The 26 AWG gauge is large enough to carry up to 2.2 amps for box wiring, which is more than ten times the 200 milliamp maximum we specified for the project. A 3.3Vdc, 26 AWG power supply seems like a good choice, but let's take a closer look.

Power cable loss

High quality 26 AWG wire has a resistance of 40.81 ohms per 1000 feet, or 40.81 milliohms per foot. With 200 milliamps flowing through the power cable, there is a voltage drop across the cable, as described below. Note that we have to run the wire from the power supply to the Arduino and then back to the negative terminal of the power supply. We can see that at three meters we have lost 5% of the 3.3 volt DC power supply. At six meters, we have lost almost 10%. This action reduces the voltage applied to the Arduino to only 4.5V; this is the lower limit of the maximum high voltage digital logic we are guaranteed.

Table 1: Line loss. The distance indicates the physical distance between the board and its power supply.

For most applications, 6 meters seems to be a reasonable distance. However, so far we have only investigated the resistance of the cable itself.

Contact resistance

Contact resistance is often overlooked or not even understood. Based on the cable cross-sectional diameter, 26 AWG cable has a resistance of 40.81 ohms per 1,000 feet. However, at any point in the wiring where we make a connection, we create a point where the cross-sectional area of the current path is reduced and, therefore, we have a point where the resistance increases.

When inserting a circular connector, the pins only touch the cylinder at the point of tangency. Spade connectors create the same reduced surface area over the entire surface. Even screw terminals cannot match the resistance of the wire section. It is important to remember that each terminal oxidizes over time and the resistance increases as the cable is connected and disconnected many times over the life of the system. Each of these points can easily have a contact resistance of 40 milliohms. This is correct; each connection point can add the equivalent of 1 foot of 26 AWG wire to the resistance. With two ground connections at the Arduino and two connections at the power supply, there are at least four connections per circuit. We now have a voltage drop of 5% at 2.5m and 10% at 3.5m between the Arduino and its power supply.

Table 2: Line Loss and Contact Resistance

A delivery option: different distances?

So, in typical power supply wiring, there is a 5% loss of 3.3 V supply voltage between the power supply and the Arduino at a distance of 8 feet and a 10% loss at a distance of 18 feet. Simply put, if we use a regulated DC power supply, we can increase the voltage to compensate for line losses and transient resistance. However, power supplies are expensive and take up a lot of space. In embedded systems, designers often try to use a common power supply for several embedded controllers. If one controller is one foot from the power supply and the last controller is 20 feet from the power supply, the designer must perform a delicate balancing act to keep each embedded controller in the proper range.

Arduino Power Options

The Arduino design allows power supply issues related to contact resistance and line losses to be solved by built-in regulation. However, there are several ways to power the Arduino, and not all offer the advantages of on-board regulation.

USB Power: To program the Arduino through the Arduino Integrated Development Environment (IDE), a USB cable is often used. the USB cable not only provides diagnostic functionality through the IDE serial monitor, but also supplies 5V DC to the Arduino through the USB Vcc pin. the 5V USB voltage is used to supply 5V directly to the Arduino or lower in the case of a 3.3V Arduino.

5V or 3.3V power: The programmer can apply the appropriate voltage to the Arduino's 5V or 3.3V power pins. These pins connect directly to the MCU power pins on the Arduino board. However, when power is applied to these pins, the Arduino MCU is susceptible to loss of power lines and contact resistance as described above.

Vin or Raw: Depending on the Arduino variant used, this pin may be labeled "Vin" or "RAW". A common mistake is to apply a 5V or 3.3V supply to this pin. The problem with this is that not only is there the line resistance and contact loss mentioned above, but this pin is also the input to the regulator IC. Like any voltage regulator, it needs to supply a little more voltage to the device than expected. If we apply 3.3Vdc to Vin, we will lose about 0.5V at the regulator, which means that the microprocessor and peripheral devices connected to it will operate at a maximum of 2.8Vdc. Combined with the observed line losses and contact resistance, we could be operating at much lower voltage levels than necessary.

Table 3: Line Loss, Contact Resistance and Regulator Loss

Pin V IN, used correctly

Despite the problems described above, the use of the V IN or RAW pin is a solution to the loss of supply voltage. On Arduino boards, the V IN or RAW pin is the input to the Arduino board's voltage regulator. Simply apply a voltage within the specified range to obtain the regulated output required by the Arduino. A supply voltage of 6 V DC to 12 V DC applied to Vin or RAW will provide power to the Arduino microcontroller, overcoming any voltage loss on the line or contact resistors, and to the Arduino's 5 V and 3.3 V pins to power peripheral components.The input voltage range of the Arduino is governed by the voltage requirements of the entire board, including the MCU's ability to supply the power needed to power the peripherals.

Applications

Standard power supplies in the 7 VDC to 12 VDC range are not as common as 3.3 VDC or 5 VDC, but they are available. It is tempting to use the more common 5 VDC and 3.3 VDC power supplies for Arduino boards, but based on the above facts, it is necessary to use less common alternatives to get the best control and performance from the microcontroller.