How to test a DMX splitter

Question

This question is related to the DMX splitter I'm building and shown in Prototyping a DMX splitter.

However, for testing a different question is appropriate.

I never really tested a hardware device, so be gentle please.

The intended use for the DMX splitter is to use on a music stage with my band(s). The device will be reasonably safe under my keyboard stand.

For completeness: for safety it has 5 optically and power-isolated input and four output channels, TVS's for each DMX output, a varistor and normal and temperature fuse for the main 220/240 AC, but no double enclosure, just one plastic enclosure.

I wanted to perform the following tests which might be typical for the intended usage:

1. Normal behavior: power DMX splitter on (and check functionality).
2. Hot-plugging input device: while DMX splitter is powered on, switch off and on DMX input device.
3. Hot-plugging output devices: while DMX splitter is powered on, switch off and on DMX output device (per output).
4. Removing the DMX input cable/plug and reinsert it, repeatedly.
5. Removing the DMX output cable/plug and reinsert it, repeatedly.
6. Power on a heavy power device on the same 220/240 V group (like a drill), repeatedly.
7. Power on a 380V 3 phase device in the neighbourhood.
8. Using 20 meters of cable per output (will be more than we ever need).
9. Connecting 8 devices per output.
10. Laying heavy power cables next/on the DMX cables (like the 380V phase cable).

Are these reasonable tests to perform or should I add more?

Answer 1

Before you start testing, here are couple observations on your posted "schematics".

1) You are missing current limiting resistor on channel 4 optocoupler.

2) The positioning of transceivers relative to DMX connectors is awful. The wires go across entire boards. Either rotate the chips or move output pins to the other side of the board so that the distance between transceiver pins and board connectors is minimal. I believe you've asked about exactly this here.

About the transceivers? I can rotate them, moving to the other side is no option, since I would use another few inches for wiring the outputs to the actual actual DMX panel mount plugs.

Other than 3 DMX pins all others are internally wired, i.e. not connected to panel jacks. If you move these 3 to the other side next to MAX487 outputs you can then rotate breadboards too, to put pins close to jacks.

Update: OK, I see it won't be quite that easy since your PCBs are stacked and wired through. Well, then I suggest rotating the transceivers. Especially because current placement puts all those DMX signal wires next to AC power distribution wires.

3) The decoupling capacitors in the picture listed as 1pF. That is way too low. Schematics suggests quite typical value 100nF (0.1uF), which is 100000pF or 100 thousand times more than you have.

4) On channel 1 there is no ground connection between DMX GND and DC-DC GND1

5) On ALL channels pin 1 (output!) of MAX487 is connected to VCC. It should be left unconnected. Only !RE connected to Vcc prevents them from instant burnout now.

6) there is only one 120 Ohm terminating resistor (on the input). You need termination on all 4 outputs as well.

Other than these, you have comprehensive set of tests planned.

There is one test that is not really fair to the splitter, but might expose vulnerabilities. It is powering off the splitter while controller remains active. Technically, input transceiver should survive this OK.

Also, let me re-emphasize the importance of using correct cables (either DMX or CAT5/6). The XLR cables have wrong impedance. While short runs can be used for testing, 20m of that would be quite taxing on output transceivers.

Answer 2

A typical certification / commissioning test sequence for consumer electronics usually includes the following:

1. Usage tests

   • Functional test (test each function / mode)
   • Performance test (test how the device performs under maximum load)

2. Power supply tests

   • Power supply variations (test with minimum / maximum voltage)
   • Power supply failure (test where the power is repeatedly lost and restored)
   • Conducted transients (test reaction to bursts / surges)
   • Conducted interference (test reaction to high-frequency noise and base frequency harmonics)

3. Environment tests

   • Temperature (cold / heat)
   • Humidity / moisture (e.g. damp heat / water mist / condensation)
   • Vibrations / shocks (test after a fall)
   • Inclinations (test the device upside down etc.)
   • Physical integrity (test if the case can withstand a certain weight or pressure)

4. Safety tests

   • Insulation resistance (test at different temperature, humidity levels etc)
   • High voltage (test if the insulation withstands a certain voltage)
   • Flammability (typically a destructive test, skip)

5. Electrical interference tests

   • ESD (apply electrostatic discharge to exposed connectors)
   • Low-frequency EM fields (stronger magnetic fields, capacitive coupling)
   • Radiated interference (test in presence of high-frequency EM fields)

6. Electrical compliance tests

   • Conducted emissions (disturbance on power lines)
   • Radiated emissions