Control/Dimming - Leprecon 612

[DCATTechie]

I was sent these picture of a Leprecon 612 the other day by a friend who was asking how a lighting board works and what all the components inside do. And I told him......I have absolutely no idea, but I bet I know a few people who do. So I was wondering if someone could drop these pics into MS Paint or an equivalent program and make a diagram labeling the parts and describing what they do. Please ask if you need more pics and I'll see if I can get him to send them to me. Could we possibly also make this a collaborative article for mine and others future reference?

[n1ist]

Start by looking at http://www.leprecon.com/productfiles...ockdiagram.pdf. This is the block diagram for this board. It shows at a high level how it works. The detailed schematic is at http://www.leprecon.com/productfiles...nschematic.pdf.

There's a processor (the large square chip) that runs a program stored in the eprom (the one with the sticker on it). This program gets its inputs from the various buttons (via some shift registers to reduce the number of pins needed on the processor) and from the sliders (via analog muxes so the processor is really only readong one at a time). Outputs from the processor go to a number of places, mainly thru some more shift registers used to add I/O pins - the LED display and status LEDs, the fader LEDs (via a DAC and some opamps to let them fade), and the analog outputs to the dimmer packs (via some opamps to boost the 5V dac output to 0-10v). There's a TTL-RS485 converter chip to generate the DMX.

The big blue cap and the chip with the heatsink are the 5V power supply.

/mike

[DCATTechie]

Still over my head. Could you explain what an eprom, shift register, muxes, DAC, opamps are? Or is there a site that explains what they do?

[n1ist]

The EPROM is a memory chip that contains the program that runs on the board. This program reads all of the inputs (buttons, faders) and generates the outputs (LEDs, DMX, analog/AMX). It does this one at a time, but repeats itself fast enough so it seems to handle everything at once.

A shift register is a serial/parallel converter. There are two types on this board, one (used for the switches) looks at 8 switches at once, on 8 pins, and lets the processor look at them one at a time on two pins. The other type lets the processor control 8 outputs in parallel (the LED display, for example) by using only two pins. These are both used because the processor doesn't have enough pins on it to handle all of this at once.

A mux (multiplexer) is a is a 1-of-n switch. In this case, it lets the processor, which has only one input that can measure an analog voltage, scan all of the faders in turn, measuring the voltage on each to determine its position.

A DAC (digital to analog converter) takes a digital number (such as 127) and converts it to a voltage (in this case, 127 would be 2.5V) to send to the dimmers. Another DAC drives the fader LEDs on the console to give an indication of brightness. The opamp is an amplifier, in this case used to convert the DAC output (between 0 and 5 volts) to the 0 to 10 volt levels that external analog dimmer packs need.

/mike