Power for Arduino Nano

The DC Power to the Arduino NANO

Abstract: This HTML page reviews the voltage supplies available to the Arduino NANO.

Possible Audience: Any enthusiasts who are considering using the Vin of the Arduino as the DC power source or the 5V and/or 3.3V outputs to power external components/shields

Keywords; Arduino Nano Vin, Voltage Regulator, FT232 (USB-RS232)

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Introduction.

The DC power for the NANO can come from three sources:

(i) The USB cable and either of but not both

(ii) External 7-9 volts (nominal) applied to the Vin pin

(iii) External 5 volts applied to the +5V pin.

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The Details

The NANO out of the box will probably be powered from the USB bus. This voltage powers the ATM328P microcontroller and FT232 (USB to RS232 converter). However the path includes a MBR0520 diode that has a nominal 0.38 volts drop so these two components are actually run off 4.6Volts.

The Arduino has a pin lalbed +5V but when the NANO is powered via the USB it will be 4.6 volts. The available output current will be determined by the USB supply.

The internals of the FT232 run off 3V3 so the FT232 includes an internal 5V to 3V3 conversion circuit. This voltage also becomes an output pin on the FT232 and an external output pin on the NANO capable of delivering 50mA.

The NANO may also be powered from its Vin pin. This pin is the input to an on-board 5 volt regulator that drives the 5V bus. When this voltage is present the MBR0520 diode isolates Vusb from the 5V bus. Vcc is now 5 volts.

Vin is typically in the range 7-9V and the current out up to 500mA. The 7V is determined by the voltage drop across required across the regulator and the 9V to limit the power dissipated by the regulator.**

Note the 3V3 voltage is still available.

**Note these numbers are mutually exclusive. With Vin = 9V a current of 500mA will require the regulator to dissipate 2Watts!.

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The NANO Reset

On power up the DTR (Data Terminal Ready) pin of the FT232 will be low forcing the reset pin of the ATM328 to hold the microcontroller in the reset state. The capacitor C2 will charge via the 1K pull up resistor releasing the reset pin. The microcontroller will start executing the bootloader code. If there is no new code to load the previous program loaded into the NANO will be executed.

If there is code to be loaded from the USB the DTR line is pulled low forcing the microcontroller into its reset mode. This code is then loaded and when complete the new program executed.

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Driving Output Devices.

With the NANO each individual output pin can drive 40mA but 20mA recommended. The total output pins but excluding the "5V" pin is 200mA.

Some devices will require more power than the NANO can deliver. For example Servo motors. In this case an I/O board with a separate power supply is required. One example is shown below:

In this example the power is taken from the model railway tracks via a bridge rectifier to provide approximately 12 volts DC. The PCA9685 board can power up to 16 servo motors. The servos are powered, independent of the NANO via a buck regulator with the output set between 5 and 6 volts**. The NANO is powered via its Vin pin from an 8 volt regulator.

In the bottom left there is an opto-coupler that extracts the PWM from the input signal and generates an interrupt to the NANO. The NANO program determines the required actions and programs the servos via the I2C signals (SDA and SCL) to the PCA9885.

**The PCA9685 shows a Vcc vooltage coming from the NANO. This pin powers the internal circuitry - it is not the power for the PCA9685.