DMX input question

[pmiller056]

I've got a new dimmer pack for LED strips. The DMX input circuit uses a surface mounted RS485 line receiver. In the past I have had to occasionally change the DMX receiver IC on equipment. This has been easy because the IC has been socketed or easily solderable by hand with simple tools. Does anyone have any useful protection circuits or devices that can be used between the DMX line and the new dimmer pack to reduce the risk of damage in use?

 

Thanks

[Charlotte_R]

Stick a buffer between the desk and the dimmers

[musht]

optoisolated buffer, Stairville/random brand 4 way metal case one was genuinely isolated

 

e2a even charge your phone

 

https://www.thomann.de/gb/stairville_dmx_splitter_8_usb_5_pin.htm

 

Tim or someone remeber the Pulsar input protection, couple of zeners or so to protect fom overvoltage?

Edited June 30, 2020 by musht

[timsabre]

Pulsar circuit was a 250v rated PTC thermistor in the DMX+ and DMX- lines, with a 5V tranzorb from each line down to ground on the "inside" side of the thermistor.

 

On overvoltage the ptc thermistor heats up and becomes high resistance, isolating the device.

 

This meant you could apply mains to the DMX line and nothing died (I tried it once)

[Brian]

How much is a new dimmer? Seems daft spending more than the cost of a new one on protection.

 

Or buy yourself an SMT workstation and learn to replace them; it's not difficult. In fact, you *might* be able to do it with a normal iron and a few tricks.

[J Pearce]

Worth saying that in 26 years of mucking around with DMX kit I've only had 1 dead DMX transceiver and that was entirely attributable to some very questionable venue wiring (DMX leads having a better path to ground than the mains earth, amongst other faults).

 

I try to always use a splitter (so a fixture fault kills that, not my desk) and keep a lowish number of fixtures on each line from the splitter - damage limitation - but this is mostly good practice rather than a hard rule borne of spending my life replacing DMX transceiver chips.

 

If you're finding you're needing to change chips a lot it might be worth checking your wiring/cables/topology/equipment for faults.

[pmiller056]

Thank you for your replies. The new dimmer packs will be used for temporary or event type work rather than a fixed installation, so they're always going to be more vulnerable to damage. I'll go with the PTC and Transzorb solution suggested by Tim for simplicity.

 

Previous damage has been noted where a laptop PC used as the DMX controller has been plugged into the earthed dimmer while operating (why's nothing working, oh, oops!). Upon investigation, the DMX line was wired directly to the line receiver IC in the dimmer with no other components around. I suspect that the leakage current (or connection transient) from the double insulated (unearthed) laptop power adaptor in use at the time may have been sufficient to do the damage.

Surface mount repair work is now a fact of life - I'd still prefer not to have to do it!

 

Thanks

Peter

Edited July 2, 2020 by pmiller056

[timsabre]

The pulsar thermistor circuit is complete overkill really. I've designed DMX products for a long time and a 22R resistor in each DMX signal line is enough to stop 99% of blow ups.

 

[pmiller056]

Tim - Noted and thank you.