The DMX-shield is an add-on (or "shield") for the Arduino. It is an easy way to use the Arduino as a DMX-Master device (transmitter), just by adding the DMX-shield on the top of the Arduino. This shield is a simple circuit based around a driver chip (MAX-485 or SN 75176). The Driver Block Outputs the 3 Pins are needed for sending DMX (DMX-Pin1 -> Reference (GND); DMX-Pin2 -> Signal inversion (cold); DMX-Pin3 -> Signal (hot)). Furthermore is the Driver Block taking care of changing the Arduino signal Voltage (0V / 5V,) into the DMX signal Voltage (-2,5V / +2,5V, according to RS485). Resistor is 100 Ohm.
If you want to quickly start developing your DMX project you can take a look at the Conceptinetics DMX Library or the DMXSerial library. These libraries can be used to easily develop your DMX project. They include examples for sketching a DMX Controller (master), DMX device (slave) or an RDM device (slave with bi-directional data transfer).
Which connectors and how to connect them?
DMX controlled equipment can come with either 3 or 5 pin depending on the design of the equipment. Lower end equipment tends to use 3 pin XLR connectors where higher end equipment tends to use the 5 pin design. The connector you use should reflect that of the equipment you are using, however adapters are available. The 5 pin design is specified in the DMX spec as a way to prevent DMX from being plugged into audio equipment, pins 4 and 5 are primarily left unused, but some manufacturers have begun to implement dimmer feedback via both proprietary and the RDM specification.
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