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I am trying to make a DMX splitter. Everything works now, but it would be somewhat useful to have notification LEDs, like in the example below.

enter image description here

For the input I could use one LED, which I either connect to the RS485 + or -. Which one does not matter, because if a DMX cable is connected the LED lights up.

However, for the outputs it does not matter if a DMX connector is attached, the LED always is on (because there is signal on the input going to the output).

How could I make a red/green or single color LED that would light up when an output connector is inserted to a DMX device?

(btw, for the input I used a transistor, to prevent a significant voltage drop from the real signal going to the LED).

I'm not asking to recreate it exactly, I just want to have a LED that lights/blinks when a signal is sent to a DMX output.

Update

I created a new question (Prototyping a DMX splitter, the schematics I copied here for completeness:

enter image description here

Circuit where the above is based upon (for the sake of this question there is no functional difference)

enter image description here

Credits to J. Mack.

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    \$\begingroup\$ It's good to see that you're at this stage with the project so you must have all the other issues sorted out. You know what's coming next: Add the schematic! Show what you've done on the input if you would like any feedback on potential problems. \$\endgroup\$
    – Transistor
    Sep 3 '18 at 9:50
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    \$\begingroup\$ Add the schematic of your circuit. I don't think that schematic of AC-DC adapter is important. \$\endgroup\$ Sep 4 '18 at 3:29
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    \$\begingroup\$ I'm all for blinkenlights, but these sorts of LEDs are of dubious benefit. Professional splitters don't generally have them, except maybe if they support RDM where bidirectional data can be indicated. Otherwise, at best you can only indicate whether or not the line is loaded, or if the splitter's transceiver is sending 'something', but that doesn't tell you anything about the actual integrity of the data at the far end, or if the data is even REACHING the far end. \$\endgroup\$
    – ajb
    Sep 10 '18 at 20:31
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    \$\begingroup\$ Based on this design I created mine. Can you look at this scheme and say what you think? easyeda.com/sergey.romanov/dmx-splitter \$\endgroup\$ Jul 18 '19 at 16:04
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    \$\begingroup\$ @SergeyRomanov It looks good (although I haven't checked details). I think you miss resistors between U2 and U1/U3/U10. I like your idea of dip switches \$\endgroup\$ Jul 18 '19 at 16:59
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If you want to detect physical insertion of connector, then you need a XLR5 socket with mechanical switch. But, maybe, better approach would be to detect a terminating resistor between A and B data lines being present.

The presence of terminator can be seen as a current flowing in/out line drivers in the splitter, so small shunt resistor or whatever else suitable method to measure current will do.

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  • \$\begingroup\$ I prefer the terminating resistor/measure since all my DMX devices use XLR3. I will check how to use a shunt resistor. \$\endgroup\$ Sep 3 '18 at 11:25
  • \$\begingroup\$ I couldn't really found small-size shunt resistors (unless you mean small resistance). They are reasonably big and relatively expensive (>1$). So probably I leave these LEDs out. \$\endgroup\$ Sep 3 '18 at 11:38
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    \$\begingroup\$ You need a resistor with value low enough to not affect driver's output significantly (something like ~ 1 ohm could do, maybe even bit more would be ok, depends ...), almost any type will do, it does not be precision resistor or any other special shunt resistor. But you need to detect voltage drop in order of mV and with lot of common-mode voltage, which means suitable amplifier, which could be quite challenging if you are really on budget. \$\endgroup\$
    – Martin
    Sep 3 '18 at 12:01
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    \$\begingroup\$ Moreover, you would need to handle the fact, that current is AC. Could be wort of try to check if current consumption of the RS485 driver itself is good measure. \$\endgroup\$
    – Martin
    Sep 3 '18 at 12:03
  • \$\begingroup\$ I will check if I have 1 ohm's resistors at hand... also adding 4 opamps will use some extra space (which I maybe don't have). But good to know it's at least possible (and I know how to do it just in case). It's just a 'nice addition' but not necessary :-) \$\endgroup\$ Sep 3 '18 at 12:03

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