8ch DMX switch pack

This pack can be wired 'multiphase' and prevents EMI due to to it's zero crossing switching. This way currents up to 160A can be handled.

A switch pack consists of:
1     DMX-Transceiver
1-8 power units

DMX-Transceiver (Rev. 3.01)

With 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

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.

power unit

The schematic is based on a datasheet of Motorola.

schematic:

Is the LED of OK1 turned on, the optotriac waits till the next zero crossing occurs and fires then the main triac via R2. R5-S is used for gate termination. R4 and C2 are the snubber network of this small circuit. All in all the circuit is very cheap but able to drive big loads.

The modul is powered via the common heat sink (similar to the dimmer). This way we can handle large amounts of current without heavy wires. Of cause such a heat sink must not be directly connected to parts you can touch!! In multiphase systems the heat sink should be connected to Neutral.

I routed a combi pcb for the power modules of the dimmer and switch packs with 4 channels and an on-board zero crossing detection (for dimmers). Dimmer and switch modules use different parts.

pcb layout (37mm x 111mm)

placement

temperature monitor

Switching large amounts of current, we have to make sure that the power modules won't get to hot. This is done with an NTC (6k8 @20°C) connected to A-In of the transceiver. For calibration move the poti R1 to the right stop and set the NTC to the shut down temperature. Now move R1 back until the red LED goes on and the pack shuts down.

stand alone mode

DIP10 enables the stand alone mode.

Debugging

A working pack 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.
	constant on	The power modules are too hot.	Wait until the temperature is OK again. Improve the heat sink. Build the temperature monitor and the A-In of the transceiver.