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 DMX LED dimmer

 

With this firmware the DMX-Transceiver generates 9 PWM channels to dimm  standard LEDs directly. If you want to control clusters, please use a driver IC and for Luxeons, etc. I recommend a constant current source.

Furthermore a strobe function is implemented. Fore more information see the channel mapping.

DMX-Transceiver (Rev. 3.01)

picture of transceiver rev.3.01With this modul DMX data can be received or transmitted.

Because of the complete usage of the RS485 converter, a bidirectional transfer of data is possible (i.e: RDM as described in ANSI E1.20). Till now this feature is only supported by a few expensive devices.

Though the circuit is only made of an AVR and few other parts I recommend a diy etched board.

 

 

 


parts

  IC1
  IC2
  IC3
  B1 
  LED1
  LED2
  R1
  R2,3,4
  C1,2
  C7
  C5,6
  SW1
  Q1
  connectors
ATmega8515-16PU
75176B
7805
rectifier (round)
LED 5mm red
LED 5mm green
10k (PT10-S)
390 Ohm
27pF
100nF
100F
DIP-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 parts around 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 the dimmer-/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:

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 be selected as clock source by changing the fuse bits.

After the mcu is set to the right clock source, the led firmware should be written to the flash of the AVR.

Driver

 standard LEDs (<30mA)

 LED Cluster

 Luxeon, Lumiled,...

(by Frank Moersen)

With a resistor single standard LEDs can be directly driven by the mcu and the board psu. Clusters need more power and should be switched driver ICs like the common ULNs. For the more expensive Luxeons I recommend a switched constant current source like the one, developed by F. Moersen.

 

channel mapping

ch1 Strobe     0-29  = Dimmer
  30-244= Strobe (0,5Hz - 30Hz)
245-255= SYNC
ch2-ch9 Dimmer 0= 0%, 255=100%; wired to Output
ch10 Dimmer 0= 0%, 255=100%; wired to A (PB0)

 

stand alone mode

DIP10 enables the stand alone mode.

DIP1-3  Chaser
DIP5-8  Speed
DIP9  Strobe

If the LEDs of your circuit react 'invers', just jumper 'spare1'.

 

Debugging

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

Pattern Error Solution
flashing There is no signal connected to the transceiver. Connect the transceiver to the DMX bus.
double flashing The signal is not accepted as DMX.
The transceiver cannot receive all required channels.
Swap D+ and D- at the DMX connector.
Transmit more channels or choose a lower start address.