It is the brain of the board. Its function is send and receive information. The following pins are available for the final user:

• Digital pins: D3, D5, D6, D9, D22 y D23. These pins send and receive digital signals, either at high level (5V) or at low level (0V).

• Analog pins: A0, A1, A2, A3, A4, A5. These pins also send and receive analog signals, that is, they are capable to manage intermediate values between 0V and 5V.

• I2C pins: The A4, D22 (SDA) and A5, D23 (SCL) pins, can also be used as I2C communication pins.

• Power Jack: Through this connector, we power supply the board. The input voltage is in the range from 6V to 15V.
• MicroUSB: Through this connector, we will supply the board with 5V and 500mA. We can also program the microprocessor, pointing out the intructions to execute.
• LDO (Low dropout) regulator: Its function is to regulate the input voltage from the Power Jack to a fixed voltage of 5V that will use for supply the following components: Buzzer, RGB LED and MCU. It is capable to manage up to 300mA.
• Switching Regulator (DC/DC): It regulates the input voltage from the Power Jack to a fixed voltage of 5V. The difference with the LDO, is that we will use the DC/DC to supply the externally conected satellites through the RJ9 connectors. It is capable to manage up to 3A.

This component is incharged of the data transfer when the USB cable is connected to the microUSB connector. It allows the MCU programming.

• Fuses were added at the entrance of microUSB and Power Jack to avoid overvoltage or overcurrent damages in the equipment.
• ESD protection component were added to avoid equipment damages because of electrostatic discharges.

Like external satellites included in the Zum Kit Junior, you can configure and program the following on board mounted components:

• Buzzer. You must set the buzzing frequency to obtain the desired tone.
• RGB LED. It means red, green and blue LEDs. Combines these three colors to produce the desired final color.

Six RJ9 connectors are installed. They allow the connection of satellites that are included in the Zum Kit Junior. These connectors are numbered and its configuration is the following from right to left:

• Connector 1: 5V, D6, A1, GND.
• Connector 2: 5V, D5, A0, GND.
• Connector 3: 5V, D3, A3, GND.
• Connector 4: 5V, D9, A2, GND.
• Connector A: 5V, A4/SDA, A5/SCL, GND.
• Connector B: 5V, D22/SDA, D23/SCL, GND.

To build optiboot for ZUM Junior the Optiboot must make with the following command: make atmega328pb LED=D2