Gertboard ATmega IO vs. Arduino Pins

The printing on the Gertboard indicated the port and pin numbers internal to the Atmega microcontroller… However this is normally hidden from the user by the Arduino’s “wiring” library and rather than refer to (e.g.) Port B, bit 5, you’d normally refer to “pin 15”.

The mapping is fairly straightforward, but to help you connect wires to pins on the Gertboard, here is a handy table to let you see what the connections are:

Gertboard
ATmega Port/Pin
Ardino
Wiring Pin
Notes
PB5 13 (LED)
PB4 12
PB3 11 PWM
PB2 10 PWM
PB1 9 PWM
PB0 8
PD7 7
PD6 6 PWM
PD5 5 PWM
PD4 4
PD3 3 PWM
PD2 2
PD1 1 TxD
PD0 0 RxD
PC5 Analog In 5 SCL
PC4 Analog In 4 SDA
PC3 Analog In 3
PC2 Analog In 2
PC1 Analog in 1
PC0 Analog In 0

Note that Pin 13 is hardwired to a small LED on Arduino Duemilanove and newer boards – it’s not connected to anything on the Gertboard.

Pins missing that you may expect to find on an Arduino are the positive and ground power connections and the analog reference voltage. This is tied to 3.3v in the ATmega on the Gertboard, so you must make sure that you take this into account when using the analog inputs. ie. you must call:

analogReference (DEFAULT) ;

when using analog inputs. Also, remember that to read a voltage, the calculation is

volts = analogReading * 3.3 / 1023.0

as the reference voltage is 3.3v.