4.1.4 MSP430 MCU Design

The MSP430 MCU is powered through a simple (and inexpensive) 3.3-V Zener diode linear regulator. Resistor R11 sets the D5 bias current to approximately 5 mA, which is significantly more than the current drawn by the MSP430. This maintains good regulation in the face of changing load currents. Because the input supply to the board is regulated to 5 V, the Zener regulator circuit experiences almost no input voltage variation.

The rotary encoder S1 allows manual control of the color interfaces of the lamp to the MSP430 MCU using two digital input pins. When rotated, this type of encoder generates two pulse trains 90 degrees out of phase. The number of turns can be determined by counting the number of pulses generated, the direction of rotation can be determined by comparing the relative phase of the two signals, and the speed of rotation can be determined by measuring the frequency of the pulses. This can be easily achieved using one of the built-in timers of the MSP430 MCU.

R4 holds the three LED power stages in a disabled state until the MSP430 has powered up and is ready to assume control. R1 and C1 provide a power-up reset for the MSP430. JP2 provides a JTAG interface to allow easy debugging and JP1 provides the connections to the optional low-power wireless interface.