Week 8: September 19 to September 25, 2011

Methodology

Power Supply Module

Battery

Power supply module may consist of DC power supply to power the stepper motors and voltage regulator to supply a regulated 5V DC power to the controller circuit and ICs. The system will require rechargeable batteries because it draws high currents and will be run more than once. The primary considerations in selecting the right type of batteries will be capacity, power, rechargeability, price and safety. Standard AA cells will be used due to availability and easy of charging and use. The power consumption of the Micromouse will be monitored to determine the capacity of the battery needed. The capacity of the battery will be based on the total power requirement and the duration the Micromouse might takes to complete the maze. Initially, a 7.2V Ni-MH (1800 mAH) might be used considering the voltage and current rating of the motor which is 3.15V and 1A/phase.

 

AA 7.2 V 1800 mAh NiMH rechargeable battery

 

Voltage Regulator

Voltage Regulator circuit consist of LM7805 3-Terminal 1A Positive Voltage Regulators, diode 4007, 2 units of bipolar capacitor 100µF, 2 units of 0.1µF capacitor, a 1kΩ resistor and an led. The purpose of using this circuit is to convert voltage from unregulated DC supply which is 7.2V to a regulated 5V DC to power the ICs and other electronic components. The LED is used as an indicator for power supply. 

LM 7805 can receive a DC input voltage within 7V to 20V and produce an output current up to 1A and output voltage within 4.75V to 5.25V. The device is equipped with thermal overload protection and short circuit protection to protect the circuit and components especially the ICs from overheating and short circuit condition.  

   

Voltage regulator using LM 7805

The above picture is the voltage regulator circuit that I have developed for testing purpose using LM 7805.

Another better alternative is by using LM 2575, a simple switcher 1A step-down voltage regulator which capable of driving a 1A load with excellent line and load regulation. It requires only 4 external components and equipped with internal frequency compensation and a fixed frequency oscillator. The LM 2575 series offers a high efficiency replacement for three-terminal linear regulators. Below is the schematic diagram for LM 2575.