Microcontroller Education Board – Power Supply25th March 2020
Power can be supplied to the board through the 2.1mm barrel jack. The power jack is center pin positive this can be identified on a power supply with this symbol:
PLEASE CHECK THIS IS CORRECT AS IT MAY DAMAGE THE BOARD IF INCORRECT.
The power input can be a DC voltage from 7-18 Volts. This power is directly supplied to the Motor Driver circuit which bypasses the voltage regulators.
There are two jumpers that can be removed to measure the current flowing through the whole board or just through from through the 5 Volt rail by replacing them with an ammeter.
The power in status LED provides an indication that the board is receiving power correctly. If the power in LED is illuminated but the 5 volt or 3.3 Volt LEDs are not, then remove the power and check for any shorts to ground. The power in status LED is protected by a 5.6 Volt Zener diode. It will ensure that the maximum voltage is limited to 5.6 Volts. If the voltage rail exceeds 5.6 Volts, The Zener diode will pass current down to ground which will create a voltage divider that remains at 5.6 Volts.
The LM7805 regulator provides a constant 5 Volt rail for all of the components on the board except from the 3.3 Volt rail on the Arduino header, the motor driver chip and the servo power rail. The regulator is capable of providing current up to 1 Amp. Warning, the regulator can get hot, especially when powering the board from a high voltage. The metal tongue on the regulator can provide a helpful ground point for crocodile style clips like on an oscilloscope probe.
The status LED can be used to check to see if the rail is working correctly. If the power in LED is illuminated but the 5 Volt status LED is not, then remove the power and check to make sure there are no direct shorts from 5 Volts to Ground.
The two capacitors smooth out the voltage rail from the output of the regulator as the boards load changes from the microcontroller.
The L78L33A regulator provides a constant 3.3 Volt rail at 100 mA for the Arduino header. It is not used anywhere else on the board.
Much like the 5 Volt rail, two capacitors smooth out the voltage rail from the output of the regulator as the load changes.