Goddard Design Company

The Method Used by the Lil'DMXter and the MiniDMXter to Convert DMX512 to Percentage

We included a percent display mode in the Lil'DMXter and in the MiniDMXter so the units could have a display that approximates the display seen on lighting consoles. The percent display mode should not be expected to exactly match any particular console, and should not be used if it is important to know the actual level that you are receiving. It should not be assumed that a Lil'DMXter transmitting 45% percent will transmit the same code as your lighting console set to '45'.

DMX512 uses an 8 bit binary byte to represent a dimmer level; this is 256 possible levels, 0 to 255. Theatrical lighting has long used a 10-point scale, which with the advent of the digital control consoles became a 101-point scale, 0 to 100. There is no integer factor to convert 101 to 256. Therefore, an integer conversion between these scales will be approximate.

At the time the Lil'DMXter was introduced there was no agreement on exactly how the rounding should be done. The table that we used reflected a reasonable match to other products then in production. The discrepancies manufacturer to manufacturer are seldom of great import in theatrical lighting although they are of some import when DMX512 is used to drive other devices, such as color scrollers.

Since the DMXters are test equipment, we have always felt that our table should be published and so it is in our manuals. We are now posting it on the Web so that it will be easily available. We do not represent this as the BEST conversion table just the one that we have used and for consistency's sake continue to use. 

Technical notes: The conversions from percent to decimal and decimal to percent in the Lil'DMXter are all table driven. When the Lil'DMXter is set to the percent mode more than one received code will be displayed as the same percent value. For example 7Fh, 80h, and 81h are all displayed as 50%. The full receive conversion table is listed below.

The RAM dimmer table always stores dimmer levels in 8 bit binary. Conversion is done when a number is displayed. Hence snapshot is re-transmitted exactly as it was received. While 7Fh and 81h are both displayed as 50%, they will be stored and re-transmitted as different levels. BUT when the Lil'DMXter is in percent mode you can only enter one value for each percent step. To find the exact values see the transmit conversion table listed below.

Lil'DMXter and MiniDMXter PERCENT TABLE

% REC'D XMIT % REC'D XMIT % REC'D XMIT
0 00-02 00 34 57-58 58 68 AD-AF AF
1 03-05 05 35 59-5B 5B 69 B0-B1 B1
2 06-07 07 36 5C-5D 5D 70 B2-B4 B4
3 08-0A 0A 37 5E-60 60 71 B5-B6 B6
4 0B-0C 0C 38 61-62 62 72 B7-B9 B9
5 0D-0F 0F 39 63-65 65 73 BA-BB BB
6 10-11 11 40 66-68 68 74 BC-BE BE
7 12-14 14 41 69-6A 6A 75 BF-C0 C0
8 15-16 16 42 6B-6D 6D 76 C1-C3 C3
9 17-19 19 43 6E-6F 6F 77 C4-C5 C5
10 1A-1B 1B 44 70-72 72 78 C6-C8 C8
11 1C-1E 1E 45 73-74 74 79 C9-CB CB
12 1F-20 20 46 75-77 77 80 CC-CD CD
13 21-23 23 47 78-79 79 81 CE-DO DO
14 24-26 26 48 7A-7C 7C 82 D1-D2 D2
15 27-28 28 49 7D-7E 7E 83 D3-D5 D5
16 29-2B 2B 50 7F-81 81 84 D6-D7 D7
17 2C-2D 2D 51 82-83 83 85 D8-DA DA
18 2E-30 30 52 84-86 86 86 DB-DC DC
19 31-32 32 53 87-89 89 87 DD-DF DF
20 33-35 35 54 8A-8B 8B 88 E0-E1 E1
21 36-37 37 55 8C-8E 8E 89 E2-E4 E4
22 38-3A 3A 56 8F-90 90 90 E5-E6 E6
23 3B-3C 3C 57 91-93 93 91 E7-E9 E9
24 3D-3F 3F 58 94-95 95 92 EA-EC EC
25 40-41 41 59 96-98 98 93 ED-EE EE
26 42-44 44 60 99-9A 9A 94 EF-F1 F1
27 45-47 47 61 9B-9D 9D 95 F2-F3 F3
28 48-49 49 62 9E-9F 9F 96 F4-F6 F6
29 4A-4C 4C 63 A0-A2 A2 97 F7-F8 F8
30 4D-4E 4E 64 A3-A4 A4 98 F9-FB FB
31 4F-51 51 65 A5-A7 A7 99 FC-FD FD
32 52-53 53 66 A8-AA AA 100 FE-FF FF
33 54-56 56 67 AB-AC AC

Reading the Table

When receiving any of the levels listed in a box in the REC'D column values will be displayed as the percentage in the '%' box in that row. Therefore 7f, 80, 81 hex will all display as 50%.

When transmitting, the value sent is the one appearing in the 'XMIT column. So for 50% we send 81 hex. Note that all transmit values were biased high. The highest value that is displayed as a particular percent value in RECEIVE is the one transmitted for that percent value.

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© copyright Goddard Design Co. 1998