DMX controllers use a "start address" to determine the first DMX channel they will respond to. Typically the first controller will use start address 1.
Some lighting controllers don't allow you to set the DMX start address at just any old value. They use the DIP switches to set a unit number instead. The possible DMX start addresses are is in blocks of "n", where "n" is the number of channels in the device). For example, with some 16 channel units, setting the "device address" to 1 is still DMX start address 1, but setting it to 2 would be DMX start address 17, 3 would be DMX start address 33, etc.
This article is mostly about the types of controllers where the value set via the DIP switch is the actual DMX start address.
DIP SwitchesThe DIP switch for setting the DMX start address is usually a 9 way switch, with some equipment using a 10 or 12 way switch. The extra switches are often for selecting optional modes of operation. Each individual switch in the DIP switch can be in either of two positions - on or off.
Weighted ValuesFor a DMX start address, the individual switches are assigned "binary weighted values" (doubling each time). Switch 1 is value 1, switch 2 is value 2, switch 3 is value 4, etc.
+ Binary Weighted Values Switch 1 2 3 4 5 6 7 8 9 Value 1 2 4 8 16 32 64 128 256
Working out which DIP switches to turn on may seem confusing, but is actually not hard once you see the relationship (above) between switch number and value.
Example 1Below is what the DIP switch looks like on a typical DJ lighting unit. The first 9 switches are for the DMX start address and the 10th switch is to select an optional function.
If you check which switches are turned on (2, 5 & 6 in this example) and add up the associated values (2, 16 & 32), you'll get 50 which is the start address. Remember, DIP switch 10 and above are not part of the address calculation. So that's how you read an existing address from the DIP switch.
Example 2Working out what DIP switches need to be on for a given address means you have to work backwards.
In this example, we want an address of 49:
- Subtract the highest weighted number you can from the desired address (49)
- That's 32 in this example, so 49 - 32 = 17
- Set DIP switch 6 on as that corresponds to the 32 in the line above
- Subtract the highest weighted number you can from the remaining number (17)
- That's 16 in this example, so 17 - 16 = 1
- Set DIP switch 5 on as that corresponds to the 16 in the line above
- Subtract the highest weighted number you can from the remaining number (1)
- That's 1 in this example, so 1 - 1 = 0
- Set DIP switch 1 on as that corresponds to the (2nd) 1 in the line above
- We were left with a remainder of 0 after that, so we're all done now!
CalculatorsThere's quite a few DMX start address calculators on the web. These allow you to either set the virtual switches on screen and see the address, or visa versa, or both:
Tables of Complete Values
Software Categories: DMX Information pages