DMX Demultiplexer

8/15/2019 DMX Demultiplexer

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IC1 IC2 IC3 B1

LED1 LED2 R1 R2,3,4 C1,2 C7 C5,6 SW1 Q1 connectors

ATmega8515-16PU75176B7805rectifier (round)

LED 5mm redLED 5mm green10k (PT10-S)390 Ohm27pF100nF100µFDIP-Switch (10)8MHz (HC49)pin header (single)

As you can see, the schematic is quite simple: The heart of the controller is the firmware of the mcu(IC1). The start address is set with SW1. The LEDs indicate the status of the controller. The partsaround IC3 are responsable for an exact Vcc of 5.0Vdc. IC2 is the RS485-Transceiver. It allows our controller to communicate via DMX512 with other equipment.

For a dimmer- or switchpack you have to connect the pins of "output" with the "-"pins of thedimmer-/switchmodules because a mcu can drive bigger loads as a current sink. The "+"inputs of all modules must be connected to vcc.

The "spare" port is used for additional pins or to jumper different modes.

AC1&2 have to be connected with a power supply of 9-12V ac or dc. 3-5W should be sufficient.

The following schematic shows you how to connect the transceiver with the DMX bus:

this is the layout:

MX Demultiplexer http://www.hoelscher-hi.de/hendrik/english/demux.htm

de 4 27/06/2012 12:04

http://www.hoelscher-hi.de/hendrik/english/demux.htm




The board is 48 * 76 mm^2. The resolution of the picture above is 300dpi.

placement:

On the resources site you can find a manual for programming AVRs. The 8MHz crystal has to beselected as clock source by changing the fuse bits.

After changing the fuse bits the transceiver should be flashed with the Demultiplexer Firmware. Thisprogram generates high frequency PWM signals from the next eight channels after the startaddress.

Filter and Shifter


de 4 27/06/2012 12:04





A PWM signal is averaged via R1 and C1and amplified by IC1A. The OP-Ampdoubles the input voltage. C2 prevents theamplification of the PWM ripple after the lowpass.

I used the quad OP-Amp LM324 in my testcircuit. Any other rail to rail OPA shouldwork, too. If the LM324 is used, connect pin4

to +12V and pin11 to GND.

The ripple can be decreased by increasingC1 and R1.

Debugging

A change of relevant channels is indicated by a flashing green LED. The red one repeats error codes until the bug is fixed:

Pattern Error Solution

flashingThere is no signal connected to thetransceiver.

Connect the transceiver to the DMX bus.

doubleflashing

The signal is not accepted as DMX.The transceiver cannot receive allrequired channels.

Swap D+ and D- at the DMX connector.Transmit more channels or choose a lower start address.


de 4 27/06/2012 12:04



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DMX Demultiplexer