DIY keychain DMX tester for lighting technicians.
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- Опубликовано: 5 июл 2024
- If you work in the event lighting industry then you'll probably have experienced DMX network issues and the mayhem they can cause. One of the biggest weaknesses of DMX is the lack of error detection and the annoying ability to function under fault conditions with random instability.
The most common problem is a shorted or broken data line in a network, and this simple tester can detect many of those issues.
Note that this tester will not analyse the validity of a DMX stream, although it's very rare that there is a data timing or format issue unless the shadiest generic lighting desks are used.
It will also not indicate a reversed data pair, although that's often fairly obvious in a run of lights.
I use one of these at work and it does a great job of tracking down faulty cables quickly.
Note that officially you are supposed to terminate a network by plugging a connector with a 120 ohm resistor in it at the end of the run of lights. The resistor bridges the two data lines and reduces the risk of signal reflections that can corrupt data at random points in the network. It's not uncommon for veterans of the industry to imply that they actually cause problems. In reality the terminator will most likely show a problem that was already there. For instance, if a broken cable left one of the data pairs floating the lights might still work with just one line, but when the terminator is connected it stops the rogue line floating and brings it to an equal voltage with the good line. That results in no differential voltage and no data, causing the lights to stop working.
The coloured connectors were bought from a UK supplier called CPC which is part of the Element 14 group, so I would expect the same connectors to be available from their other outlets around the world.
Here are some connector purchase links for the UK.
For the 5 pin male XLRs the codes are:-
Red - cpc.farnell.com/pro-signal/ps...
Yellow - cpc.farnell.com/pro-signal/ps...
Green - cpc.farnell.com/pro-signal/ps...
Blue - cpc.farnell.com/pro-signal/ps...
Black - cpc.farnell.com/pro-signal/ps...
For the 3 pin male XLRs the codes are:-
Red - cpc.farnell.com/pro-signal/ps...
Yellow - cpc.farnell.com/pro-signal/ps...
Green - cpc.farnell.com/pro-signal/ps...
Blue - cpc.farnell.com/pro-signal/ps...
Black - cpc.farnell.com/pro-signal/ps...
Quarter watt 220 ohm resistors:- cpc.farnell.com/unbranded/mcf...
And whatever bright red LEDs you can find, noting that eBay generics are fine.
Choose a bright connector colour to make it easier to spot in amongst the blackness of the industry. I keep mine on my keyring at times to make sure it's always with me. The slight downside of that is the risk of inadvertently leaving your keys plugged into a light!
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.com/coffee.htm
This also keeps the channel independent of RUclips's advertising algorithms allowing it to be a bit more dangerous and naughty. 
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I miss working in lighting. Its one of the only jobs I never got tired of and enjoyed immensely. My wife gives me crap because every time we go to a show i spend more time looking at the lighting and pointing out malfunctions than i do the show lol.
How do you get into lighting? I'm a plumber atm but I really wanna do lighting lol
@@TheDoctorPretzel Originally i started with staffing agencies around me. they would send me out as a stagehand on various shows, basically as a grunt to do the heavy lifting. A friend of mine worked at PRG, a large production house and i got in there. they were always looking for people because the management was insane and kept running people off lol. i could care less so i lasted quite a few years before my office laid off half the staff. still do freelance stuff but it's not nearly as exciting.
COULDN'T care less, you mean.
@@simontay4851 this
I'm 15 and I stare at lights wondering why the hell that mover is set to the wrong address!
Y'all gon' make me test my lights, up in here, up in here...
Mr Clive on behalf of all lighting technicians we love you and please keep this up ✌
8:26 Post it as a blooper video. I'd watch it haha. Clive waiting for glue to dry 10 hours version.
Stranger Patreon exclusive
I have the link to it...but...
One of the first things we built as apprentice telephone engineers was a test lamp that worked the same way. We had official issue ones but - 2 carbon filament lamps soldered to a 10" piece of thick grading wire as a probe, a long switchboard chord provided power (almost exactly the same as clive's) except not using LEDs was far more sensitive. Plugged into one of the many 50v dc jacks on every equipment rack in the building. They were all you ever needed ... very rare that anyone used a meter for faulting the old strowager equipment. The carbon filament was fairly dim and didn't hurt to look at them to see the subtle changes in brightness. With a bit of practice you could see a difference of only a couple of ohms.
I would have soldered the metal "key ring" to Ground, so that you could easily short it to any ground to better debug the (local) ground
That is a gosh dang good idea.
In v2.0, perhaps? :-)
fuckin hell manuel, thats a pro gamer move
Nice!☺
I would not do that, just because I've heard of situations where line voltage has ended up on DMX cable due to very bad gig electricians wiring trusses wrong. Because of the way DMX is implemented in good gear, fixtures can work just fine even in this crazy situation in a rig that's not bolted down to grounded metal.
me: no heat-shrink tubing?
bigclive: I like to live dangerously
the glue is the insulator
It is, unless something shorts out before you apply glue. When he was sliding it in case, I had quite bad feeling about it.
I was thinking the same thing as he was stuffing it in the shell.
Heat shrink is your friend. Always wear protection.
@@robertc1161 Noticed the "whisker" as well.
I love all of your videos, but this one in particular I really loved because stage lighting is a niche hobby that I've been interested in for years. Thanks for the content!
Really nice to see you dive into more technical stuff. I worked a lot with RS-232, but rarely encountered RS-485, especially in those applications, fascinating and very instructive. Would like some more deep analysis like that.
The mumbling had it's charm! It was interesting to compare the versions of the video.
The DMXCat is one of the most useful tools ever, I use them constantly and they're worth every cent they charge for them.
Right after the multitool podger, the dmxcat is my most used tool!
Thumbs up for talking about DMX.
Rolled my own controller some years ago from a raspberry pi and a dongle, now a days you can drive DMX directly from the pins(through some circuitry for a more robust signal). Took a crash course in DMX formatting and timing. Its not perfect, but its a damn simple standard. Very neat too look into.
Always amazed at your soldering dexterity
More videos like these please!
- Touring LX tech
Now we need a videjo showing these DMX glitches!
McDonald's paper thingys for putting sauce in are great for mixing epoxy in, as are the wood coffee stirrers for stirring it. Those paper thingys are actually designed for you to pull the edge so that they open into a saucer for greater capacity !
This is for a very specific usage, indeed. I didn't even had the knowledge of such device (DMX tester) but I find this build very appealing to watch.
Love the channel and you Sir "Big Man", your voice is so relaxing . So informative and respect, thank you so much.
So many things to take away from this: Dollar Store has resin, and those little shot glasses (which I have also seen there) are perfect for mixing up some resin, and not caring about the container you mix it in. And to save even more money, I can steal coffee stir sticks from a coffee shop on the Isle of Man. :D
A coffeshop of a victim of a horrible accident.
A note for all non Isle of Man inhabitants, a certain fast food chain, with a big yellow M as a logo also carries very similar stir sticks.
@@3vIl3aGl3 - MITROPA?
Decades ago when I was still in the industry, I made several similar testers to verify phantom power in audio systems.
The only changes are higher value resistors (phantom can be up to 48 volts) and making sure the LEDs are connected in the correct orientation (phantom is DC)
pileofstuff I make phantom testers too. You don’t even need resistors, because the phantom power spec includes 6.8k resistors built into the mic input. My little testers are literally just a male XLR insert, two LEDs, and a bit of hot glue to keep it together.
@@Scodiddly I put the resistors in as much to protect the system against my tester as anything.
sounds like the widget i could do with to test our 50v dc jacks on our MDF's (+/- 50v)
this is indeed a very useful device and these have saved me countless times
This is great. I just inherited two universes on a side gig that have some serious issues; address swapping, flickering, pulsing, full drop out etc......I'm fairly new to DMX so this is awesome, making one today. Thanks.👍
There sure is a lot of shit that can go wrong in the world of DMX lighting, so eliminating things like cable or pure signal loss can be extremely valuable!
One of the things I learnt pretty early on was that it´s always nice to use a splitter and separate fixtures that are fed from different powerphase on separate isolated DMXlines(each line on their own splitter output). While it often works fine even if you just run a single line even if say the strobes are running on their own phase, it can create problems. Groundhum is a thing for lights as well :P
So a good opto-isolated switch is something I bring on basically all gigs, often more than one. It separates fixtures from each other, FOH/desk from the fixtures and it can simplify cable runs a lot :)
I have gotten by without a tester like this, partly because many of our lights will show if they have DMX and not, but I will be building atleast one! This design is as Clive says wastly superior to the older ones with just the bicolor LED.
I built one using XLR4 for testing scollers, with an extra LED, zener and suitable resistor between pin 1 and 4 for testing the power supply as well. Was an absolute godsend, as while the scollers themselves were usually pretty well looked after, the PSUs were quite often neglected...
As part of my job I took a course on troubleshooting. The trouble shooting method you talked about is officially called "the half-split method" and is useful for everything from wiring to complex electronics, breaking a system in half and looking for goesintas and goesoutas. Great Video!
In computer programming, it's known as the "Binary Search" algorithm.
EnjoyingUTube Too Or simply "bisecting", the name also used in math.
Thanks Clive, as always, an informative and useful video. I am one of your new peatrons, wish I had found you earlier!
Hot melt glue will flow better if you warm it up with a hot air gun after it's been put in place.
It will also stick better to metal surfaces as they get warmed : gluing to a cold metal surface will set too fast and easily break away.
Yes, this. I use my hot air a lot to make hot melt glue flow better and tidy up the annoying stringy bits.
Brilliant idea! and I can think of two people who would love one of these in their Christmas stockings ❤️
learnt more about wirening, electronics, voltages and resistances from a few videos here than middle, high, college and university
"Con-rod" would also be a term for an engine part - connecting rod, the part that connects the piston to the crankshaft. But by your description of him, he's that special fastener that's only in existence on a few vehicles - the nut that connects the steering to the seat.
Top performance motorcycle racing on narrow winding roads...
All of them are totally insane xD The only race I ever saw, a guy lost control and slammed into the side of a pub. He wasn't moving so I don't know if he survived or not...
@@rich1051414 I'm familiar with that crash. He was killed instantly.
I love that. Will build one myself. Thank you Clive
I just watched a very fascinating video about the Isle Of Man during WWII. I had no idea how important it really was. Kudos to the British people back then.
I like any kind of pocket tester like that, I am going to build one, and it gave me some ideas for some other handy testers. thanks!
Just made one but used a red and a yellow LED (old style). Works great and this way you know which line isn't ok.
Thanks for the tip.
"Just under a quarter of an inch, say about five millimeters" You managed to confuse Americans and Europeans both in one sentence!
@Matt Quinn I didn't say he was inaccurate.
A quarter OF an inch.
@@simontay4851 You're getting pedantic.
Luckily, I grew up in Britain through the 'gubbing up' of our measurement system, and learned to use both metric and imperial measures. I am the grandmaster of confusing people with my measuring system - sometimes, for fun, I'll refer to chains and furlongs, or decimal fractions of an ounce. It keeps people on their toes. 😁
One meter equals 6.68 times 10 to the minus 12 astronomical units. I supply this information for my arithmetically challenged fellow US citizens.
Once again, I find myself gently blowing on the monitor to cool the soldered parts :)
Don't blow on your soldering!
We do the same for A and B signals plus their compliments coming back from shaft encoder.
Nothing to beat visual indication.
Thanks great use of fingers to hold things. I have been wiring all types of these plugs and sockets for years. It is useful to get a piece of wood board and screw the opposite connector to it. You can then plug your plug or socket in and it is held securely while you work. I have one board with DIN, D, XLR and others types on it.
Thank you Big Clive. I am currently playing with an Arduino and a DMX shield board and this will be a nice trouble shooting or debugging tool. Just like my old RS-232 RX TX tester .
22:22 who else caught themselves leaning their heads to see around the shot glass while he was pouring?
3D RUclips one-day...
I totally did that. Had to stop myself, too. Like, wtf am I doing?
Glad I'm not the only one!
Yep!
I so wish they had standardized on the transformer isolated RS-485 version that Apple selected for its LocalTalk network system in the 1980s. By doubling the clock speed (but not the data rate) and using biphasic modulation with a tiny 1:1 isolation transformer at each node you end up with a variant which needs only the 2 twisted pair wires and has no ground reference, while keeping number of loads relatively unaffected compared to vanilla RS-485. As a bonus it’s polarity insensitive and completely eliminates the hazards of ground loops through the data connections.
Peter S The technique is still standard in Ethernet over twisted pair, with the highest speeds using 4 transformers for 4 pairs, while lower speeds use only 2 pairs and 2 transformers.
@@johnfrancisdoe1563 Correct you are. While it's proven itself as a great method of sending data point to point, it also works wonderfully for RS-485 busses with a single transformer per node. DMX came about just before digital had matured enough to make it a much more robust standard. I used to work for one of the founders of AVAB America who had a part in the early switch away from AMX to digital and the ideas that eventually turned into DMX. He went on to make Internet of Things devices back in the early 1990s before the Internet had been opened to commercial use (I was a designer there) and he moaned constantly about how he would have gone the route Apple went if he had only known.
Why not put a 3rd LED (possibly of another colour) across the data pins? That way you'd be 100% certain of the fault.
Very cool, I shall make a few of these for my toolbox and for down at the theatre!
I once slightly dabbled with DMX but not enough to have a fault with it !
As for a tester of that ilk, I did make a pair for 1980s Ford brake pad wear warning lights - on the basis that the warning light does not distinguish which wheel was indicating the fault. The pair I made, one showed a fault and one didn't - as the system had a self-fault indication too - so with the two 'testers' one could 'plug n play' ones way around the wheels to trace the fault without dismantling anything.
I had no idea about DMX, until I watched James Bruton use it with his robots, had no idea it was so simple and I'm surprised it's not more popular with hobbyists...thanks for the explanation.
There is similar ideas, different speeds and error correctness even some with transceive capability. Some to look up is rs485, ic2, packet, rtty, psk, qam64, fsk, OFDM & CCK (used for your WiFi)
Most of these can be run over wires so it's point to point but with the correct equipment you can transmit all this over the radio spectrum, afterall its telemetry
Have you ever picked up the cropped off lead thinking it was your piece of solder and wondered why it wouldn't work?
This is awesome. Thanks so much for sharing.
Thanks I will be using this! And just FYI the connector is numbered on the back side. Both 3 and 5 pin are that way.
a 3rd, dual color LED across 2 and 3 would help you diagnose open grounds and open cables
I was going to suggest something similar. Without some kind of a third LED, an open ground is the same indication of not plugged in at all. That makes a difference in what you're looking for.
Old mains testers had 3 neons to test for mixed up wiring. Having an indicator between the data lines would check to see if data was there or if the lines had been shorted.
@@dave0smeg modern ones still do this for mains (at least USA consumer grade testers)
I made a couple of improvements (you might have covered these I jumped forward) - different leds per "channel" to tell which is down and
I'd use the + to - test as a "if this lights but the others don't ground is out".
I was a lighting tech for summer stock theater back in the early 70s. We had rheostats, variacs and SCR dimmers but no DMX. A few years later Popular Electronics ran an article showing how to build one of the first digital dimmer controls using, I think, an 8080A MPU. I considered building one but the theater lighting industry was unreliable at best so changed to a different career path. It was fun though, a lot of work but fun, and you got to hob-nob with the actors, some of whom were famous or would go on to become famous.
You drew a local chassis ground at the fixture, but often "good" gear only has a floating reference ground in an isolated receiver to reduce ground loops. In practice, this means the DMX signals can float above the fixture ground by potentially hundreds of volts (depending on who and how it was made) and still work just fine!
The most common configuration for pro gear is DMX grounded at the console or distribution box and floating at all receivers, which guarantees no ground loops.
Lower quality gear (usually any XLR-3) is much more likely to be grounded at every node.
brilliant -- going to make up a few, and add pairs of red LEDs to some of our terminators as well!
The terminator resistor will defeat the ability of the tester to identify a broken line. It will provide a low impedance current path between them. You can do it with the simpler version though as an indicator.
That 'double chopsticks' technique with your left hand is my take-away from this video!
"quadridextrous" ?
Really? I have a book about Tartans and all - and it contains a like really long chapter on Bonnie Prince Charlie and all of that history stuff, but.nothing.about.Scottish.soldering.technique. Want refund.
Interesting! Thank you Big Clive!
The resin cures in one second..for us. Love You Clive!! (Not in an unsavory manner). :-)
To make hot melt glue flow in better you can also use a heat gun from a reflow station to warm it more (or pre warm the parts)...just keep the bottom cool if it has holes. Upside down canned air can do a nice job of speed cooling hot glue around holes as i dribbles.
can't wait to see how many kids start showing up to calls with these ...
One my long term projects is to make my own version of the swisson. This could be a fun little project to check small issues.
Thanks Clive.
I seem to remember that the DMX refresh rate is 50Hz for all 512 channels. It's interesting to note that a PIC micro with a serial port can be used to generate a DMX512 stream (running at 20MHz) - if you abuse the serial port slightly (to generate the long break and mark after break that DMX uses)
Quite a while ago seeing you do finger gymnastics, I would so need my helping hands for that (and taking quite a bit more time indeed)
Superb sir.thankyou kindly.
XLR-3 pin... worth mentioning that pin 1 was nominated as ground - because they connect before pins 2 & 3. Originally in high-gain mic circuits to minimise plug-in/out noise.
When building stuff like that, I like to use black hot melt, to keep the light from one LED from slightly illuminating the other. Probably doesn't make any practical difference in this case but sometimes bleedover between leds is unsightly or misleading.
So this thing can tell me where the hood at?
I looked in the comments specifically for this and you might be the only RuffRider
What? WTF does that mean.
WHAT WHAT
ARFFF ARFFF Shut em down open up shop
😂 Flash of my flash plug of my plug
My grandparents once was on Disneland and we watched the video tape back at home. And on one tape it was first ok but then a video of a dangling camera filming the ground, and the camera raises up to show the surrounding and...CUT...and then you saw the surroundings and the camera went down dangling showing ground again. And then once again, it was raised and..CUT... and so on, several times. Quite funny actually =)
The Simplicity of that reminds me of the old Auto Electrical tester one of the magazines put out. Might have been Electronics today International or equivalent in the late 1970s. You had a red and a green LED with about five or six combinations that's basically covered most wiring faults a vehicle
Clive, can you review a fishing bite alarm? the one that monitor the line doing pass inside. they have a rubber wheel and magnet inside.
I'd solder the loop of copper wire to the ground lug for extra security while dangling on the keychain.
Cool just got around to watching the rest of your video and their was an ad for the wago connectors you showed us awhile ago. Coincidence ?
As a person who has worked as local crew I resemble that remark lol
Omg thank you so much....just made my own
on small things like that, I tend to loop the component leads around hooked through each other snugly, then solder. that makes it less prone to vibration issues since it's mechanically hooked.
hot glue works great for holding the stuff apart and sealing the LED end, I wouldn't fill the whole tube solid. if you want to pot it, just use hot glue to seal the back side connector/pins first, just don't have it facing down where the glue will run down into them. of course silicone/caulking will work, but it takes far too long to set up!
clearly, I needed to watch further before commenting, since you did more or less the same thing with the glue.... maybe I'm a mind reader and don't know it :)
I still remember the instructor in Army basic electronics training telling us about the split-half troubleshooting method. It seemed so obvious to me that I wondered why he even mentioned it. That was 46 years ago. I since realized that it is not intuitive for many people.
Chris W in software development it’s called a binary search. It is the fastest way to find a random value in an ordered collection. And errors in a cable are just that.
Yeah, it was still 'taught' as a basic fault finding method at SEE in the late 80's. I was a REME CET
What time 2 part epoxy do you use? I have sometimes used 5 min epoxy and mix for say 2-3 minutes it gets thicker and easier to pot with before curing.
I bult it and used a dmx endresistor with a flat metal back and just drilled a hole in the middle of it, looks very neat. But i had to use a 2 color led cause of the limited space. It will defenately help me in the future. thx
How many times have you left your keys plugged in a light then? Also. Could you use diffrent colour LEDS to determine what pin is getting power?
Just a thought... The copper loop to fasten in the keyring? Solder one end to the casing lug, then do a 90° either to the center of the connector or along the inner circumference run it perpendicular to the axis of the connector for a bit (this is so the casing lug won't take much strain when the keyring loop is tugged at). Other end of loop like Big Clive did.
Reversals on RS485 over fibre were something I found irritating. "Hang on I'll reverse my end, nope", "You reverse your end, nope", "I'll straighten my end"...... and so on.
Thinking you could've done without the red shroud as well. Would make it even shorter and more compact. Personally I'd have used some heat shrink around the leads as well, I know it's all potted but just in case.
Excellent stuff! I was able to follow thus tutorial and make my own, which works great!
Any suggestions for making something similar to test for existence of (+48v) phantom power..?
You can probably find a schematic for that on the 'net.
I did something similar for an RJ45 cable tester.
I made up dongles that would give me a binary readout on the tester unit so that I could confirm which trace outs went where.
thanks a lot！
good video！
but any idea of making a tester for audio？
If you have an old phone you can just set to continually vibrate, it's great for resin!
love it, mate
How often are you working with Ethernet for lighting control? And are you seeing Cat5 cable being used for DMX cabling. Seeing this slowly migrating into service here in the USA, but the majority is still "standard" shielded twisted pair XLR cable.
It varies from job to job depending on the designers preference, but typically it's just ethernet between the desk and DMX rack. Fibre optic makes a more frequent appearance now.
You can use red high efficient leds, they use current but give way more light
I saw a video (metallica rigging fail) where hydraulic arms crashed, they were supposedly controlled by dmx which failed (i think i was told the program corrupted).
Is there a watchdog circuit available ?
If not, i guess you could have a watchdog system that looks for data (just a couple of opto isolators that are given an on/off command) connected to a charge pump, if the pulses failed, this would drop out a relay in a stop circuit for the arms (or any other mechanical device that could cause damage)
Is that possibly the "staged" stage accident with "truss" falling onto the stage, a crew member going on fire, a rigger "falling" unconscious from the rig and other stuff? Nothing critical gets controlled by DMX unless there are code sequences built in to prevent rogue activation.
I started to wonder when the guy caught fire and no one seemed to be panicking to put him out.
Also that metaallica didn't seem to panic either.
Thanks for clarifying :)
(Staged) ruclips.net/video/mP2hcW2--5c/видео.html
For that resin stuff you should get a couple of these veterinary syringes without needels. Used to give pasty medicins like deworming stuff. Use one to apply marine grease on me and my buddys RC boats.
I wonder if you could use an adapter, like a 5pin -> 3pin, (they even make them?)or use the screw threads in the base to join both connectors into one unit
Also, would Bi-Color LED's indicate the pin reversal scenario? Blinks Red (or Green) for OK, and Green (or Red) for Reversed?
I noticed hitting Epoxy with a hot air gun for a few seconds directly after pouring pops most bubbles on and near the surface, so you get a clean surface after curing.
Can you use 1 resistor from ground instead of one each from the positive and negative? If you don`t cut the resistors so short, is it possible to bend them and force them into the receptacle. Then the will not fall out that easy.
Great question, the issue is if the cable was wired wrong, the other led will be passed full voltage and current, so if the dmx had a nice strong 5v rail it'd then pass through the one led (say it was a 2v led) and then in reverse breakdown of the other led to ground etc, it's almost 2am here for me so I might not make much sense lol but if the led had reversed voltage and it then passes through the resistor then its very low current, (maybe 2mw depending on the led voltage being used)
@@ianharvey868 I don`t think revers polarity is a problem in this circuit. A red LED can handle more than 5V in reverse. Anyway, I will build a couple of these. Thanks Big Clive.
This is a great idea - I think I'm going to make a mini DMX light on a keyring that actually has an address, and can be faded for testing too :) I think I would have used different coloured LEDs for the + and - pins though.
Stabby666 Watch from 7:00 again ;-)
Would a third bicolor LED between data pins be good to tell if data has power but ground is open?
What kinds of demands do you get from the venue on what lights go where? I'd imagine it's very specific and you get given requirements for what types of lights should be in what exact positions and how they need to be hooked up to control circuitry, or is it that specific? What's the depth of control you get over how a given install/setup should go?
The lighting is designed by the lighting designer who provides drawings of where everything goes and how it's addressed.
Nice tutorial! Will certainly make one. Does it double as a terminator?
No it doesn't. Adding the termination resistor would effectively bridge the network lines and give false results.
@@bigclivedotcom ok! Thanks!
I'll actually have to make one of these. I work A/V at fan conventions often and we get just enough DMX issues that it'll be handy for fault finding. (though it also helps if the show file is properly mapped STEVEN AGAIN GOSHDARNIT THE PARS ARE ON 8 CHANNEL MODE NOT 5)
I did lots of RS485 networking about 30 years ago and a simple tester like this can save you hours of headaches. You might want to consider creating a couple variants, one of this design and another with a pair of reverse biased gallium nitride LEDs and a small resistor of 100 to 220 ohms between just the data lines. Between those two testers, you can diagnose almost any cable fault at a glance with ease.
To make it even more compact you could use a bicolor LED, or two colors from an RGB one
Great little tool. Would it cause any issues having this circuit permanently installed in a dmx line?
It would pose a slight extra load and might affect the number of lights you could run on a network.
Similar devices but with added zeners are used to test microphone 48v phantom power