Microplex (MPX) Project

This project will allow you to build an interface from your PC to Microplex dimmer boxes. The Microplex (MPX) project is a collection of the interface and supporting software. The primary purpose was to link lighting control to sound and music. It is recommended that you have a Microplex based lighting control system or knowledge of it before reading the following articles.

Microplex Protocol Specification (As best we know)

The Microplex protocol is a proprietary analog multiplexing lighting control protocol used primarily by NSI (Leviton). It is sent across standard XLR (Microphone) cable. Three wires are used which are +12v, GND and Signal. From our examination the Microplex protocol can handle up to 100 channels. However, the more channels, the slower the refresh rate.

The Microplex signal line swings from +8v to -6v. This was learned by examining the signal on a scope. The actual specification could be different. +8v is Fully ON and 0v is Fully OFF. Negative voltage, -6v, is a sync pulse.

The protocol starts off by sending a 5ms sync pulse. This sync pulse resets the channel counter in the dimmer boxes to zero. After the pulse, the level for the first light is send for 0.25ms. If the light is to be off, then the level will be zero volts. Next a 0.25ms sync pulse is sent. This increments the channel counters on the dimmer boxes. The 0.25ms pulses are repeated until all the channels have been sent. The process begins again with the 5ms sync pulse.

The frame time (time from one 5ms sync pulse to the next) can be calculated with the formula t = 5ms + (2x * 0.25ms) where x is the number of channels and t is in milliseconds.

Windmeter / Anemometer Circuit

The circuit for the Windmeter is self powered. A 12v solar cell array provides power to the circuit and charges the battery during the day. At night the 12v battery is used to power the circuit. Operation for many days without sunlight is required, so the circuit operates at 3.3v and uses a high efficiency switching power supply. The circuit draws 1.35 mA at 12v. The circuit should operate for over 50 days without sunlight from a fully charged battery. The solar cell will take 3 days to fully charge a dead battery. The circuit should never loose power.

Power enters the circuit through L7 and D1 to prevent reverse battery connection. C10 is used as a input filtering capacitor while C11 is used as a input de-coupling capacitor. U3, L1, D2, and C12 form the switching power supply. R3, R6 and R7 form the low battery power down.

A magnet and Hall effect sensor are used to measure RPM of the rotating cups. One pulse per revolution is produced. The sensor is on the back of the PCB and the magnet is attached to the rotating shaft. Microcontroller U2 is used to calculate wind speed from the pulses produced by the Hall sensor. The micro also records the varying speeds and provides a interface to a Laptop / computer. U1, a low power RS232 1 channel driver, is used to join the PC serial port and the micro's UART. C2 - C5 are used by the RS232 Driver IC to form charge pumps. C1, C6, C7, C13 are used as bypass / de-coupling capacitors throughout the circuit. C8, C9 are used to help start oscillation. The crystal of 4.096 Mhz was selected for easy and accurate time measurement. R1, R2 are used to form a voltage divider which feeds ADC channel 0 to measure Supply voltage. Q1 and Q2 control the power applied to R1 and R2 to improve power consumption.