Renard
Overview
Renard is the name of a computer-controlled, PIC-based dimmer scheme, and is also applied to the dimming controllers that people have built based on this architecture. The designs all use mid-range PIC micro-controllers, are generally modular in units of eight channels (dimmable circuits), and use medium-speed, daisy-chainable, one-direction serial communications for input. Renard controllers do not have stand-alone show sequencing capabilities, and rely on a separate computer (usually a PC) to send it real-time sequences of dimmer commands.
This design was originally described in the Simple PIC-Based 8-Port Dimmer 'How-To' on the http://computerchristmas.com website in a generic form. Since then various people have designed and built controllers based on this hardware, and there are likely to be coop buys of one or more of these designs. Renard is strictly a DIY, hobbyist effort at this time, with no commercial products available (either software or hardware).
How Does Dimming Work
The Pieces and How They Connect Together
Comparison with Other Schemes
LOR AL D-LIGHT DMX-512
Future Directions
Number of Circuits (Channels)
The number of Renard channels that can be supported on a serial port depends on both the baud rate and on the frequency of updates that has been programmed into the Vixen sequence. The most common PC control software is vixen, which easily supports multiple serial ports (including USB-RS232 and USB-485 converters).
With an update interval of 100 ms and a 57600 baud rate, the number of channels that can be supported (worst case) is 288. There are a few dimmer levels that are sent using a two-character sequence (dimmer levels 125, 126, and 127 out of 255), and this worst case number is intended to handle the situation where the brightness level of all of the channels has been set to one of these levels.
Protocol
Version 1
Character Format
Baud Rate can vary, current firmware is programmed for 57600.
1 Start Bit, 8 Data Bits, No Parity bit, 1 Stop bit (8N1)
Special Characters
0x7D - Pad byte, silently discarded by controller firmware, inserted by host PC to prevent Tx overrun 0x7E - Sync byte, start of packet marker. 0x7F - Escape byte, used as prefix for encoding dimmer levels that correspond to the special characters.
Packet Format
Byte 0 - 0x7E (sync byte) Byte 1 - Command/address byte (usually 0x80, see below) Byte 2-n - Dimmer values (0-0xFF, values 0x7D, 0x7E and 0x7F have special encoding, all others are sent raw)