# Homemade DMX Tester



## McCready00 (Dec 28, 2008)

Make a DMX tester.


I made it and it seems to work well..

Anyone made it and have any comments on it?


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## Wolf (Dec 28, 2008)

Look cool, and I cant wait to make one. 

Although I would like an example of how to make one with a 4-pin connector. Does anyone instructions for the 4-pin? Would it still be pins 2 & 3


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## derekleffew (Dec 28, 2008)

Congratulations, McCready00. I'd like to think you found the link to those instructions in our Collaborative Article: http://www.controlbooth.com/forums/...cles:DIY+DMX:+Demux,+Protocol+Converters,+etc.


Wolf said:


> ...Although I would like an example of how to make one with a 4-pin connector. Does anyone instructions for the 4-pin? Would it still be pins 2 & 3


Probably (but depends on your scroller or other gadget) it would be pins 2&3, see http://www.controlbooth.com/forums/lighting/7714-color-scrollers.html#post90957. As long as you're building one, consider another LED of a different color or style, to verify voltage between pins 1&4. Do not use on Morpheus ColorFaders.

Send me one when you're done.


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## McCready00 (Dec 28, 2008)

here's the one I've done last week.


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## TheDonkey (Dec 28, 2008)

That looks brilliant!

I haven't read this specific article, but I remember in some othe guide, someone said to put 2 LED's in pararell, but reversed, and of a different color, that way you can see if the "data" is actually changing.

Did the LED fit in the hole that well naturally, or did it take some knifing/force?


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## McCready00 (Dec 28, 2008)

I used the actual hole that was pre-made. It worked perfectly. 

And I've used a bi-colour led ( red/green ).

Paid something like a 1$ for the resistors and the led.


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## TheDonkey (Dec 28, 2008)

McCready00 said:


> I used the actual hole that was pre-made. It worked perfectly.
> 
> And I've used a bi-colour led ( red/green ).
> 
> Paid something like a 1$ for the resistors and the led.



Oh ok, that LED only looks like it has 2 leads so I assumed it was a one way...


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## FMEng (Dec 30, 2008)

A bi color LED is essentially two LEDs in one package. The two LEDs in the package are different colors and polarities, with a common pair of leads.

Keep in mind what this tester can and cannot tell you. It can tell you there is a signal pressent, and possibly that the signal varies. It cannot tell you if the voltage swing is correct, corrupted in some way, or has noise on it. But, this little tool could come in handy.


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## derekleffew (Dec 30, 2008)

It will tell you quite a bit, actually. See http://www.dfd.com/pdf/tstrdata.pdf. I'm assuming the DIY model conveys all the same information, but I may be wrong about that.


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## TheSwami (Jan 3, 2009)

Just out of curiousity McCready, did you purchase your 5-pin XLR connector locally, or order it from the internet? I've been collecting the requisite materials for this same project, but I have yet to find a local store that carries the connectors...

73


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## tcahall (Jan 3, 2009)

This is on my list of things to put together. However, while it does tell you if the signal is alive, it doesn't help you with voltage, etc. Has anyone built one of these with test ports to access the signal with a multi-meter? If you pot it, you will need something inserted to ensure access (and hope the resin doesn't seal your path), but it would be a great addition to the tool.

Tim.


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## waynehoskins (Jan 3, 2009)

I'd like to see one with a scope built-in. That's probably harder to do, though, put a scope with a 3RP1 tube into the back of an XLR backshell.


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## tcahall (Jan 3, 2009)

A scope in a tester could be a real challenge. However, rather than connecting the resistors directly to the connector, it should be pretty simple to insert a couple of binding posts between the connector and the resistor (or LED). This would provide access for any level of testing equipment that you should choose to apply.

Looks like I have a trip to Radio Shack coming.

Tim.


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## lieperjp (Jan 8, 2009)

Help! I want to build a terminator. Does it have to be a 120 ohm resistor? My local Radio Shack only carries 100 ohm and 150 ohm (half watt). Could either one of those work?


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## waynehoskins (Jan 8, 2009)

lieperjp said:


> Help! I want to build a terminator. Does it have to be a 120 ohm resistor? My local Radio Shack only carries 100 ohm and 150 ohm (half watt). Could either one of those work?



I think it's close enough. That's the bench tech in me talking. Those are typically ten percent values anyway, so your "150 ohm" resistor may be anywhere between 135 to 165 ohms, and a 120 ohm resistor might be as high as 132 ohms.

Closer value and tighter tolerance is better, but close is close.


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## McCready00 (Jan 8, 2009)

Here is what Nick Mobsby wrote inside his book called Practical DMX : 

"The value of the resistoris a function of the characteristic impedance of the cable. This is the natural impedance, in Ohms, of an infinite length of the cable. Such a length of cable is defined as being 'free of reflections'. Typical cables used for an installed DMX network, such as Belden 9842, have an impedance of 120 Ohms. Most cable range in impedances between 90 ans 150 Ohms. Values close to the characteristic impedance will also work. For this reason I recommend the use of a termination resistor value of 120 Ohms."


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## TimMiller (Jan 9, 2009)

you can buy 5 pin connectors from Digi-Key Corporation - USA Home Page Mouser Electronics - Electronic Component Distributor Altex Computers and Electronics or Home - Ace Electronics

as far as resistors go i use 120 ohm 1% (5% at the most) 1/4 watt. All you are trying to do is terminate the signal, so the only wattage pulled is that of the resistor.


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## LDash (Jan 13, 2009)

I've just ordered a 5 pin xlr plug to make one of these 

I've been meaning to do it for months now and because i am going to need it in a couple of weeks.

i hope i dont go and melt the plastics on the plug with the soldering iron now .haa.


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## DAE (Jan 13, 2009)

I use seperated leds so I can see if one is not responding which would indicate a driver ic problem. If you use a combined bicolour led it is hard to see seperate activity as one led die is always brighter that the other.

An led has a typical voltage drop of 2.2 volts so if you want to expand on this range of led testers, put a zener diode in series with the led so you know it will not light up untill it exceeds a voltage, so you can see if your scroller supply volts is in range.


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## Chris15 (Jan 14, 2009)

derekleffew said:


> It will tell you quite a bit, actually. See http://www.dfd.com/pdf/tstrdata.pdf. I'm assuming the DIY model conveys all the same information, but I may be wrong about that.



I am going to suggest that yes you are wrong about that. If you read the spec sheet for Doug's

> If neither LED lights: common (pin 1) may be open, both lines may be stuck low, or no signal is being sent.



Now with the backyard version, there is no connection to ground and thus there can be no comment about ground. On that basis, I contend that the DIY would be less useful than the real deal...


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## CavezziMagnum (Jan 14, 2009)

Ok, I've made both 3-pin and 5-pin versions of these DMX Testers that are only testers and not testers/terminators. They are only good for testing if they is any signal coming through. Per tester I used (1) 270 ohm resister 1/2watt, 1 bi color LED (red/green), and some heat shrink-tubing and a bit of solder. It is more RED when there is a lot of signal going through (ex: controlling 3 moving lights at once), otherwise it is an orange-peach type color. It all fits neatly into the existing housing sent with the 3-pin connector.

Good Luck!


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## theisbr (Jun 3, 2012)

So I have to order some parts from an electronic store and thought I would order some LED's to make a couple of DMX testers, but when I pulled up the LED's on the Arrow website, it came back with 50,000 choices. I was hoping someone could help narrow down my selection. Are there some specifications I need to look for in an LED to put into the testers?

Thanks.


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