Fig. 2 · Arduino

Arduino Nano

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The Uno's brain on a board the size of a stick of gum, made to plug into a breadboard.

Lessons 0/4Assembly not done

Each lesson runs your own code on the board. Finish its checks to tick it off.

The Nano (A000005, revision 3.3) has the same ATmega328P at 16 MHz and 5 V logic as the Uno, on a 43.18 × 17.78 mm board with two rows of 15 pins 0.6 in apart, so it straddles the middle of a breadboard. USB comes in on a Mini-B socket and goes through an FTDI FT232RNL USB-to-serial chip, which also resets the 328P for uploads. You get 14 digital pins (6 with PWM), 8 analog inputs (A6 and A7 are analog only), 32 KB of flash of which 30 720 bytes are free for your sketch, 2 KB of RAM and 1 KB of EEPROM. There is no barrel jack: power it from USB, from 7-12 V on VIN, or from a regulated 5 V on the 5V pin.

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Every header pin of the Arduino Nano
Header	Pin	Name	Functions	Level	Max current	Notes
J1	1	TX1	D1, TXD, PCINT17	5 V	20 mA	Serial TX. It also goes to the FT232 through a 1 kΩ resistor, so the Serial Monitor sees everything sent here.
J1	2	RX0	D0, RXD, PCINT16	5 V	20 mA	Serial RX, driven by the FT232 through 1 kΩ. Anything wired here (a Bluetooth or GPS module) can block uploads.
J1	3	RST	RESET (active low), PCINT14	5 V	–	RESET, active low, with a 1 kΩ pull-up to 5 V. Same net as the other RST pin and the RESET button.
J1	4	GND	GND	–	–
J1	5	D2	INT0, PCINT18	5 V	20 mA
J1	6	D3	PWM OC2B (490 Hz), INT1, PCINT19	5 V	20 mA	PWM from Timer2. tone() uses Timer2 too, so it stops PWM on D3 and D11.
J1	7	D4	T0, XCK, PCINT20	5 V	20 mA
J1	8	D5	PWM OC0B (977 Hz), T1, PCINT21	5 V	20 mA	PWM from Timer0 at 977 Hz. Timer0 also counts millis(), so leave its settings alone.
J1	9	D6	PWM OC0A (977 Hz), AIN0, PCINT22	5 V	20 mA	PWM from Timer0 at 977 Hz.
J1	10	D7	AIN1, PCINT23	5 V	20 mA
J1	11	D8	ICP1, CLKO, PCINT0	5 V	20 mA
J1	12	D9	PWM OC1A (490 Hz), PCINT1	5 V	20 mA	PWM from Timer1 at 490 Hz. The Servo library takes Timer1, which stops PWM on D9 and D10.
J1	13	D10	PWM OC1B (490 Hz), SPI SS, PCINT2	5 V	20 mA	PWM from Timer1. As SPI SS it must stay an output while the Nano is the SPI controller.
J1	14	D11	PWM OC2A (490 Hz), SPI MOSI (COPI), PCINT3	5 V	20 mA	PWM from Timer2, and SPI MOSI (COPI). Also on ICSP pad 4.
J1	15	D12	SPI MISO (CIPO), PCINT4	5 V	20 mA
J2	1	VIN	LDO input, 7-12 V	–	–	Input for the 5 V regulator: 7-12 V, 15 V absolute maximum. No reverse-polarity protection.
J2	2	GND	GND	–	–
J2	3	RST	RESET (active low)	5 V	–	The same RESET net as J1 pin 3.
J2	4	5V	+5V rail, in or out	5 V	–	The 5 V rail: an output on USB (about 4.65 V) or VIN (5.0 V), or a regulated 5 V input.
J2	5	A7	ADC7, Input only	5 V	–	Analog input only (ADC7): no digital I/O and no pull-up, so digitalRead(A7) does not work.
J2	6	A6	ADC6, Input only	5 V	–	Analog input only (ADC6): no digital I/O and no pull-up, so digitalRead(A6) does not work.
J2	7	A5	ADC5, I2C SCL, D19, PCINT13	5 V	20 mA	I2C SCL for the Wire library. There are no I2C pull-ups on the board; most modules bring their own.
J2	8	A4	ADC4, I2C SDA, D18, PCINT12	5 V	20 mA	I2C SDA for the Wire library.
J2	9	A3	ADC3, D17, PCINT11	5 V	20 mA
J2	10	A2	ADC2, D16, PCINT10	5 V	20 mA
J2	11	A1	ADC1, D15, PCINT9	5 V	20 mA
J2	12	A0	ADC0, D14, PCINT8	5 V	20 mA
J2	13	REF	AREF, ADC reference	5 V	–	ADC reference, decoupled by 100 nF on the board. Never feed a voltage here while analogReference(DEFAULT) is active.
J2	14	3.3V	3.3 V out from the FT232 (50 mA)	3.3 V	50 mA	3.3 V out from the FT232, 50 mA at most. Never feed 5 V into it.
J2	15	D13	SPI SCK, LED L, PCINT5	5 V	20 mA	Drives the L LED through 1 kΩ (about 3 mA), with no buffer. Because of that load, INPUT_PULLUP on D13 does not read HIGH reliably. Also SPI SCK, so L flickers during SPI transfers.
J4	1	MISO	D12, SPI MISO	5 V	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.
J4	2	5V	+5V	5 V	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.
J4	3	SCK	D13, SPI SCK	5 V	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.
J4	4	MOSI	D11, SPI MOSI	5 V	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.
J4	5	RESET	RESET (active low)	5 V	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.
J4	6	GND	GND	–	–	ICSP pad. The six pads are left bare on the Nano: press a programmer's pogo pins or a header onto them to burn the bootloader.

Sensors and actuators this board drives, with the real connections.

LEDSupply 5 V
A 5 mm LED from a PWM pin through a 220 Ω resistor: about 12 mA on USB, bright and safe.
Part pin Board pin
A D9Wire colour orange
K GNDWire colour black
Careful
Never without the resistor: an LED straight on a pin pulls far more than the 40 mA maximum and kills the pin or the LED.
Push buttonSupply 5 V
Between D2 and GND with pinMode(2, INPUT_PULLUP): pressed reads LOW, no resistor needed. D2 is also interrupt INT0.
Part pin Board pin
1 D2Wire colour blue
3 GNDWire colour black
PotentiometerSupply 5 V
A 10 kΩ knob as a voltage divider: ends to GND and 5V, wiper to A0. analogRead gives 0-1023.
Part pin Board pin
1 GNDWire colour black
2 A0Wire colour yellow
3 5VWire colour red
Light sensor (LDR)Supply 5 V
A light-dependent resistor from 5V to A0 plus a 10 kΩ resistor from A0 to GND: more light, higher reading.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour yellow
TMP36 temperature sensorSupply 5 V
Analog temperature sensor: 0.5 V at 0 °C plus 10 mV per °C. Read it on A1 and keep the leads short.
Part pin Board pin
+Vs 5VWire colour red
Vout A1Wire colour yellow
GND GNDWire colour black
Piezo buzzerSupply 5 V
A passive buzzer on D8 plays tone(8, 440).
Part pin Board pin
+ D8Wire colour orange
− GNDWire colour black
Careful
tone() takes Timer2, so PWM on D3 and D11 stops while a tone plays.
SG90 micro servoSupply 5 V
Signal on D9 with the Servo library (it takes Timer1, so PWM on D10 stops too).
Part pin Board pin
SIG D9Wire colour orange
GND GNDWire colour brown
Careful
Feed the red wire from a separate 5 V supply whose GND joins the Nano's GND. A stalling servo pulls about 1 A, which browns out the Nano on USB and trips the polyfuse.
HC-SR04 ultrasonic sensorSupply 5 V
Ultrasonic distance sensor, 5 V: Trig on D9, Echo on D10, distance = echo µs / 58 cm. A 5 V board needs no level shifting for its echo.
Part pin Board pin
VCC 5VWire colour red
Trig D9Wire colour yellow
Echo D10Wire colour green
GND GNDWire colour black
MPU-6050 IMUSupply 5 V
GY-521 breakout with an MPU-6050 at I2C address 0x68 (0x69 with AD0 high). Its own regulator lets it run from 5V; SDA goes to A4 and SCL to A5.
Part pin Board pin
VCC 5VWire colour red
GND GNDWire colour black
SCL A5Wire colour yellow
SDA A4Wire colour blue
Careful
The chip itself is 3.3 V. The breakout pulls SDA and SCL up to its 3.3 V, and Wire.begin() also turns on the 328P's weak pull-ups to 5 V, so the bus idles a little above 3.3 V. It works in practice; a level shifter is the clean fix.
SSD1306 OLED displaySupply 5 V
0.96 in 128 × 64 OLED at I2C address 0x3C, on A4 (SDA) and A5 (SCL).
Part pin Board pin
GND GNDWire colour black
VCC 5VWire colour red
SCL A5Wire colour yellow
SDA A4Wire colour blue
Careful
Read the pin order on the silk: some modules are GND VCC, others VCC GND, and swapping them kills the display. Its 1 KB frame buffer takes half the Nano's RAM, so keep text in flash with F("...").

Part pin	Board pin
A	D9Wire colour orange
K	GNDWire colour black

Part pin	Board pin
1	D2Wire colour blue
3	GNDWire colour black

Part pin	Board pin
1	GNDWire colour black
2	A0Wire colour yellow
3	5VWire colour red

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour yellow

Part pin	Board pin
+Vs	5VWire colour red
Vout	A1Wire colour yellow
GND	GNDWire colour black

Part pin	Board pin
+	D8Wire colour orange
−	GNDWire colour black

Part pin	Board pin
SIG	D9Wire colour orange
GND	GNDWire colour brown

Part pin	Board pin
VCC	5VWire colour red
Trig	D9Wire colour yellow
Echo	D10Wire colour green
GND	GNDWire colour black

Part pin	Board pin
VCC	5VWire colour red
GND	GNDWire colour black
SCL	A5Wire colour yellow
SDA	A4Wire colour blue

Part pin	Board pin
GND	GNDWire colour black
VCC	5VWire colour red
SCL	A5Wire colour yellow
SDA	A4Wire colour blue

Power inputs

Mini-USB cable (5.25 V)4.75–5.25 Vup to 500 mAReverse-polarity protectedA 500 mA polyfuse (F1, trips at 1 A) and then a Schottky diode (D1). The diode stops a VIN-powered Nano from feeding your computer, and it costs about 0.35 V, so the 5V rail sits near 4.65 V on USB. The Mini-B plug is keyed, so it cannot go in backwards.
Supply on a header pin (7 V)7–15 Vrecommended 7–12 Vup to 800 mANo reverse-polarity protectionNothing but the regulator: there is no reverse-polarity diode on VIN. The 5 V regulator (an LD1117 on boards made today) limits current and shuts down when hot, but 7-12 V is the range to use and 15 V destroys it. Every volt above 5 turns into heat: at 12 V, each 100 mA of load costs 0.7 W in a tiny SOT-223.
Supply on a header pin (5.25 V)4.75–5.25 VNo reverse-polarity protectionNone. The 5V pin is the 5 V rail itself: feed it a clean regulated 4.75-5.25 V and you skip the regulator and the diode. Above 6 V the ATmega328P is past its absolute maximum, and a reversed supply goes straight into the chips. Don't feed it while VIN is also powered.

Rails

VUSB · 5 V · up to 500 mAUSB 5 V after the polyfuse. It reaches the 5V rail only through the Schottky diode D1.
5V · 5 V · up to 800 mAThe board's main rail: the MCU, the FT232 and the ON LED run from it. It is 5.0 V from the regulator when VIN is powered, about 4.65 V from USB, or whatever you feed the 5V pin. The higher source wins, because the diode turns off when the regulator's output is above USB minus its drop.
3V3 · 3.3 V · up to 50 mA3.3 V from the FT232's own small regulator, 50 mA at most. It is an output: enough for a sensor, not for an ESP8266 or an nRF24L01 radio.

Pin current

20 mA per pin
40 mA absolute maximum
200 mA for all pins together
Resets below 2.7 V
Draws about 27 mA idle
Each pin can give or take 20 mA safely and 40 mA at the absolute maximum; all pins together 200 mA through the chip's supply pins. A HIGH output is 5 V, so it can damage 3.3 V parts without a divider or level shifter. A 3.3 V signal into the Nano reads as HIGH, with little margin (HIGH starts at 3.0 V). The board draws about 27 mA on its own: about 9 mA for the 328P at 16 MHz, 15 mA for the FT232 and 3 mA for the ON LED.

Header

Name

Functions

Level

Max current

Notes

TX1

D1, TXD, PCINT17

5 V

20 mA

Serial TX. It also goes to the FT232 through a 1 kΩ resistor, so the Serial Monitor sees everything sent here.

RX0

D0, RXD, PCINT16

5 V

20 mA

Serial RX, driven by the FT232 through 1 kΩ. Anything wired here (a Bluetooth or GPS module) can block uploads.

RST

RESET (active low), PCINT14

5 V

–

RESET, active low, with a 1 kΩ pull-up to 5 V. Same net as the other RST pin and the RESET button.

GND

–

INT0, PCINT18

5 V

20 mA

PWM OC2B (490 Hz), INT1, PCINT19

5 V

20 mA

PWM from Timer2. tone() uses Timer2 too, so it stops PWM on D3 and D11.

T0, XCK, PCINT20

5 V

20 mA

PWM OC0B (977 Hz), T1, PCINT21

5 V

20 mA

PWM from Timer0 at 977 Hz. Timer0 also counts millis(), so leave its settings alone.

PWM OC0A (977 Hz), AIN0, PCINT22

5 V

20 mA

PWM from Timer0 at 977 Hz.

AIN1, PCINT23

5 V

20 mA

ICP1, CLKO, PCINT0

5 V

20 mA

PWM OC1A (490 Hz), PCINT1

5 V

20 mA

PWM from Timer1 at 490 Hz. The Servo library takes Timer1, which stops PWM on D9 and D10.

D10

PWM OC1B (490 Hz), SPI SS, PCINT2

5 V

20 mA

PWM from Timer1. As SPI SS it must stay an output while the Nano is the SPI controller.

D11

PWM OC2A (490 Hz), SPI MOSI (COPI), PCINT3

5 V

20 mA

PWM from Timer2, and SPI MOSI (COPI). Also on ICSP pad 4.

D12

SPI MISO (CIPO), PCINT4

5 V

20 mA

VIN

LDO input, 7-12 V

–

Input for the 5 V regulator: 7-12 V, 15 V absolute maximum. No reverse-polarity protection.

GND

–

RST

RESET (active low)

5 V

–

The same RESET net as J1 pin 3.

+5V rail, in or out

5 V

–

The 5 V rail: an output on USB (about 4.65 V) or VIN (5.0 V), or a regulated 5 V input.

ADC7, Input only

5 V

–

Analog input only (ADC7): no digital I/O and no pull-up, so digitalRead(A7) does not work.

ADC6, Input only

5 V

–

Analog input only (ADC6): no digital I/O and no pull-up, so digitalRead(A6) does not work.

ADC5, I2C SCL, D19, PCINT13

5 V

20 mA

I2C SCL for the Wire library. There are no I2C pull-ups on the board; most modules bring their own.

ADC4, I2C SDA, D18, PCINT12

5 V

20 mA

I2C SDA for the Wire library.

ADC3, D17, PCINT11

5 V

20 mA

ADC2, D16, PCINT10

5 V

20 mA

ADC1, D15, PCINT9

5 V

20 mA

ADC0, D14, PCINT8

5 V

20 mA

REF

AREF, ADC reference

5 V

–

ADC reference, decoupled by 100 nF on the board. Never feed a voltage here while analogReference(DEFAULT) is active.

3.3V

3.3 V out from the FT232 (50 mA)

3.3 V

50 mA

3.3 V out from the FT232, 50 mA at most. Never feed 5 V into it.

D13

SPI SCK, LED L, PCINT5

5 V

20 mA

Drives the L LED through 1 kΩ (about 3 mA), with no buffer. Because of that load, INPUT_PULLUP on D13 does not read HIGH reliably. Also SPI SCK, so L flickers during SPI transfers.

MISO

D12, SPI MISO

5 V

–