hardware description of Arduino board based on ATMEGA8 or ATMEGA168

1. Arduino - Hardware
Some Points to Remember

2. PWM (PWM-AT168) PIN 0/1 JP0 SERIAL
GND REF ENABLE
AREF
R1 0V 13 12 11 10 9 8 7 6 5 4 3 2 1 0
T2
R2
TX
RX
C1 C2 C3
LED0(Tx) PIN 13
R5 R7 R8
LED1(Rx)
R6
PIN 2(TxD)
PIN 3(RxD) R3 16MHz ICSP
MISO SV
PIN 4(DSR)
SCK MOSI
PIN 5(GND)
RST GND T1
RESET C9
S1
C6 C7
C5 C8
D2
D3
R4 R9
L1 R10
SDA
SCL
D1 POWER
R11
12V C4
AUTO RESET
RST
NC
GND 5V 0 0 9V 0 1 2 3 4 5
DC1 ANALOG IN
LED14 (POWER)
JP4

5. Points to remember
• When talking about pins on arduino, it is never ic
pins but pins on connector as marked. (refer to
previous sheet to see mapping)
• Arduino has totally 20 I/O pins
• Out of which six are dedicated for Analog
• Pins 0 to13 are digital 0 to 13 and written on the
board.
• Analog pins are 0 to 5 and written on the board.
• They are also accessed as digital 14 to 19 (not
written on the board)

6. Points to remember
• Pin 0 is also used as RX and 1 as TX. So if using
serial port, use 0 and 1 for RX and TX.
• Analog 4 and 5 (or digital 18 and 19) are SCL and
SDA. When using I2C ics use these pins.
• Pin13 is on board LED.
• For Ananlog input use ANALOG 0 to 5.
• Pin 8, 10 and 11 are PWM and is used for
dimmable LED or creating analog voltage. Pin 3,5,6
are also PWM and are found only in ATMEGA 48/
88 / 168.

7. Points to remeber
• So when starting a new board, first allocate analog
inputs, rx, tx, scl, sda, led and PWM as these signals
can only be used on certain pins.
• Then use rest of the pins as general purpose I/O
pins.
• Unused signals (say ANALOG inputs or PWM) can
be used for general purpose digital I/O pins.
• Digital pins 11,12,13 are used for programming.
Take care and do not connect and low impedence
load or any other output.