# 4-pin "scroller cable" rules



## theatrelighting (Jun 25, 2010)

Alright, everybody has heard about things you "need" and "don't need" to do when working with 4 pin! Here are some questions I think we should discuss on one thread:
Does 4-pin need a return? Is it product-specific? Is a terminator even required?
How far can you run a 4-pin DMX cable before experiencing a drop in voltage? Is there a limit to how many DMX products you can have in a single chain of 4-pin DMX?

Any others?


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## derekleffew (Jun 25, 2010)

First, let's obliterate any reference to the term "4 pin DMX." (Many will state emphatically that there's no such thing as "3 pin DMX" either, but that's for a different discussion.) I've changed the name of this thread. Even though 4-pin XLR cable (2 pins for power and two pins for data) may be used for many gadgets other than scrollers (some LED fixtures, DMX Irises, gobo rotators, etc.), the industry seems to have settled on "scroller cable" being the most widely used term. Let's also not forget other legitimate uses for the XLR4 connector.


derekleffew said:


> You might start by convincing the world's largest lighting production company, who uses:
> "XLR" to refer to any 3-pin data cable
> "RAM" to refer to any 4-pin data + power cable, including LEDs
> "DMX" to refer to any 5-pin DMX cable. ...




I'll let other members answer the rest of the questions, including an "Others?": Does the pin-out really matter?


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## xander (Jun 25, 2010)

theatrelighting said:


> Does 4-pin need a return? Is it product-specific? Is a terminator even required?


I'll answer these together because I think they are similar. The return cable has always been a touchy subject. Some people swear it is unnecessary, others, the opposite. In reality, you should always do what the product manual says to do. I treat it like a terminator, if you can, why not do it. It may work without it, but why take the risk? Some PSUs don't even have a return input, so it isn't always possible, but do it when possible. Yes, a terminator is required, if not using a return line, that is. The data on the pins is the same data and is just as susceptible to reflections as it always is. It doesn't care how many pins are in the connector. 

theatrelighting said:


> How far can you run a 4-pin DMX cable before experiencing a drop in voltage?


Every PSU is different. Look it up in the user manual for your specific product. It *may be* measured in "head feet" which is not to be confused with "linear feet" so be careful.

theatrelighting said:


> Is there a limit to how many DMX products you can have in a single chain of 4-pin DMX?


The limit would be the same as for any DMX run, but I have a feeling you would run out of power on those lines long before you every reached the data limit.

derekleffew said:


> Does the pin-out really matter?


Yes, different companies have approached the 4-pin pin-out differently. Because there isn't a standard (as far as I know) you can end up having power and data on different pins for different products. Make sure you are using the correct power supply for the products you are using or you may end up with 24VDC attached to your DMX driver chip and data running to the motor and then don't we look sheepish. 

-Tim


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## mstaylor (Jun 25, 2010)

xander said:


> ...Every PSU is different. Look it up in the user manual for your specific product. It is usually measured in "head feet" which is not to be confused with "linear feet" so be careful. ...



Having never used a scroller myself, I have hung plenty on other's rigs, I have never had to figure 4 pin usage. This means I have never heard the term head feet as opposed to linear feet. Could you define what head feet is or how to calculate it. I would ask why the difference but that may be a,"Because the manufacturers did that way."


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## Scarrgo (Jun 25, 2010)

Head feet = PSU + 50' + Scroller + 50' + Scroller =
First scroller 50'
Second scroller 100'
Total length 150'
Hope this makes sense

Sean...


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## derekleffew (Jun 25, 2010)

mstaylor said:


> ... Could you define what head feet is or how to calculate it. ...


(Psst, Michael, see the wiki entry Head-Feet. [Second time today!] )

Although other manufacturers may use a similar calculation method (but I'm not aware of any), the term "head-feet" is exclusive to Wybron.
From http://www.wybron.com/products/color_changers/coloram/manuals/Coloram_IT_user_manual.pdf , page 23:

> *Head-Feet Restrictions*
> The HEAD-FEET parameter is a method of accounting for the voltage drop in the
> power/signal cable caused by the current drawn by each color changer.
> To help understand this issue, think of it as water pressure (voltage) in a hose (cable)
> ...


It might be worth noting that Wybron power supplies don't have a provision for a return cable. Nor does Wybron require that the 4pin be terminated (citation).
One more note, Forerunner is the only Wybron product compatible with Apollo/Rosco/ChromaQ-type power supplies.


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## xander (Jun 25, 2010)

derekleffew said:


> Although other manufacturers may use a similar calculation method (but I'm pretty sure Apollo doesn't), the term "head-feet" is exclusive to Wybron.



I'm sorry, I didn't realize "head-feet" was a manufacturer specific term. I have never used an Apollo scroller and the last time I used a Chroma Q was a few years ago. I guess I am just so used to Wybron now that I assumed. I have edited my previous response to reflect this revelation. 

-Tim


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## Sean (Jun 25, 2010)

derekleffew said:


> One more note, Forerunner is the only Wybron product compatible with Apollo/Rosco/ChromaQ-type power supplies.



That is _not_ true.

The "IT" line of devices use the same power supplies as the Forerunners.


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## derekleffew (Jun 25, 2010)

Sean said:


> That is _not_ true.
> The "IT" line of devices use the same power supplies as the Forerunners.


I based my statement on the fact that here, under the "Specifications" tab, Apollo lists the Forerunner but not any other Wybron devices. While it _may_ be _possible*_ to run "IT" devices from an Apollo/Rosco/ChromaQ-type power supply, I'm sure it would not be recommended, as all of the "InfoTrace" features would be lost.


*Apollo's Smart Color PRO Manual.pdf states:

> Wybron Coloram II or Wybron IT power supplies are not compatible and cannot be used. Serious damage to the SMART COLOR PRO will occur if these power supplies are used. Damage caused by an incompatible power supply is not covered by the warranty.


Brand X's scrollers may work on brand Y's power supply; but that doesn't mean that brand Y's scrollers will work on brand X's power supply.


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## GreyWyvern (Jun 25, 2010)

Without going into much detail on the Wybron stuff, they do some things differently than other manufacturers. While the others have one pin out configuration across all of their products, Wybron has a couple different ones. The Forerunner line, as already stated, uses the same configuration as other manufacturers with pin 1 carrying 0 Volts DC and pin 4 carrying 24 Volts DC. However, on their other lines, pin 1 is 24V DC and pin 4 is 0V DC. Which brings us to the issue. If you plug a device into the wrong power supply, you will very likely let out the magic smoke. However, some devices, such as the Smart Color PRO, have built in protection that can keep the magic smoke from being released. However, as some of you have found out first hand, the original Smart Color does not have that protection.

Now with that being said, I'll move on to the cable. Apollo has pretty specific 4-Pin Data Cable Specifications that we state in our Smart Color manual, on page 23 (page 5 of the linked PDF) and quoted below.


> *4-Pin Data Cable Specifications*
> 
> Pin 1 - 0 Volts DC
> Pin 2 - Negative Data
> ...



One thing that came to our attention very recently concerns the shield. There seem to be a couple schools of thought on this. We state that the shield should be connected to the chassis of the connector at *both* ends of the cable. However, others will only connect it at one end or not at all. The shield is what you would think, a shield. More specifically, a shield from RF interference. It also serves the purpose of a ground bond. Now this is where things get dicey. For it to work as an RF interference shield, both ends need to be connected, which is why Apollo states that. On the flip side, if your power supply were to flake out and cause voltage to stray to the common ground, you would not want the shield attached at both ends allowing your accessories to "go live" with the power supply. Now, yes the breaker* should trip, but if it didn't or someone happened to be touching an accessory, it could be bad.

*Remember, power supplies should *NEVER* be plugged into a dimmed source!

Now I'll move on to the return line debate. This is something else that seems to differ between manufacturers. Apollo recommends the use of a return for two important reasons:
1) to maintain line voltage and minimize voltage drop along the length of the run and
2) to terminate the data signal (done in the circuitry of the power supply).
We realise that this is not always possible, which is why we offer a 4-pin Data Terminator. As stated on that page (_emphasis_ mine):


> The Apollo 4-pin data terminator is a useful device to eliminate data reflection in a _short-run_ 4-pin system. _Total cable length from PSU to last accessory should not exceed 100 ft._, or voltage drop may result. Remember, a 4-pin cable connecting the last accessory to an Apollo PSU will properly terminate the data signal. Without some type of data termination, poor fixture performance may result.



Which brings me cable length/distance. I don't really understand the whole "head-feet" thing, but I haven't ever really tried to either. So just to be sure things are clear from my end, I'll cover what Apollo states. It has been brought to my attention that there is a little more confusion than I was even aware of. You'll notice in the quote above that the total cable length from PSU to last accessory should not exceed 100 feet. However, from page 5 of the Smart Color manual (linked above):

> Note: Total cable length per circuit must not exceed 200 feet/60m.
> The use of a 4-pin return line must be used to minimize voltage drop
> and allow maximum performance. Route the 4-pin return cable from
> the last scroller back to the PSU 200W, 400W or 600W to maintain
> line voltage across the system, and to terminate the data signal.


There, the total cable length of 200 feet includes the return line. So it still stands that the total cable length from PSU to last accessory should not exceed 100 feet. If you are using one of the Apollo 75W supplies that has no option for a return, your total cable length can be 100 feet and I would suggest using one of the 4-pin Data Terminators. If using one of the other supplies, you are still limited to 100 feet from PSU to last accessory because the return line would put the total at 200 feet, the limit.

Now to be clear about what I just said, that limit has to do with the power, not the data. The data can go much, much further than that. The resistance of the cable with regards to the power causes about a 2V DC loss in 100 feet. Couple that with the momentary voltage drop that occurs when all the scrollers on a line are given a command all at once, and you start to see random scrollers randomly resetting. The return line greatly minimizes that.

Hopefully, that will help clear some things up, but feel free to ask if there are more questions or I need to better clarify something.

Thanks


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## derekleffew (Jun 25, 2010)

Thanks, Dave, for that very thorough explanation. Thanks also for the cool picture, from the Manual cited above:


DL's Photobucket

I've always wondered, but this is the first I've ever heard about connecting the shield to the shell (usually a big no-no in the audio world).

Where I was going with the pin-out question was "Does it matter how the cable is wired (as long as power is on pins 1&4 and data [sometimes DMX, sometimes proprietary] is on pins 2&3) ?" I.e. "Is Apollo cable different than ColoRAM cable, than IT cable, than Morpheus cable, than ColorBlast cable?"


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## GreyWyvern (Jun 25, 2010)

But wait, there's more!!! Just a couple questions and answers along the same lines.

1)Q: How far can you run a 4-pin DMX cable before experiencing a drop in voltage?
A: It depends on the guage of the wire in the cable, and the amount of current the devices pull. So just use the largest conductor available, quality XLR connectors rated at 10 Amps, and under 200 feet including return for the full loop.

Like I said in my previous post, about 2V drop per 100 feet of cable. That is from testing that we did here at Apollo. Also, to be honest, 200 feet is already a bit of a stretch. Unlike a power supply, where when it says, 200 watts and you can put 210 watts on it and be okay, 200 feet is already well pushing the limit for normal operation. Any further than that, we cannot guarantee normal operation. However, YMMV and I am not speaking for other manufacturers. Refer to the manual for what ever device you are using. Also, the largest conductor you can fit into an XLR4 connector will typically be 14AWG.

2)Q: Is there a limit to how many DMX products you can have in a single chain of 4-pin DMX?
A: This is a tricky one. The answer an either/or. The limit will be determined by either the power limit or data limit, which ever comes first. The max is driven by the total current of all devices, not to exceed 10 amps, and data buss limit of 32 DMX loads (DMX 512 spec). While the 32 load max on the data buss is specifically meant for the 5 pin DMX cables and devices, it also applies to the data on 4 pins. But power usually gets there first. In reality, current loads on 4 pin cables will hit max well before data load does.

Thanks to my upstairs comrade and occasional CB lurker GaryKuntz for posing the questions and answers.


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## GreyWyvern (Jun 25, 2010)

derekleffew said:


> Thanks, Dave, for that very thorough explanation. Thanks also for the cool picture, from the Manual cited above:
> 
> DL's Photobucket
> 
> ...



Dang! An hour and a half I spent on that post to be sure I was including everything I meant to and making sure it was all right, and something still slipped my mind. That is something I meant to mention.

The quick and easy answer is no, it does not matter as long as the pin-out is correct.

The reason we (and other manufacturers say the same thing) say "Use only our cable" is because we know it has been made to our strict specs. The main issue we have with people making their own cable is that they don't always use the correct cable. You would not beleive some of the stuff I have seen poeple try to use as 4-pin cable. _"Well no **** your scroller is working! Have you looked at what you are using to connect it the power supply with?!"_ (Hopefully I'm not about to throw myself under the bus with this next part, but...) You can build your own cable as long as you do it right. Here's a hint: If you look in our manual, we even tell you some of the things to be sure to do and give you the handy picture Derek posted above!

Now, I am sure there are some subtle (and other not so subtle) differences between manufacturers cable, but just be sure the pin-out is right. The 24V DC doesn't care or even know what color the insulation is on the wire it is running through.


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## derekleffew (Jun 25, 2010)

GreyWyvern said:


> ... You would not believe some of the stuff I have seen people try to use as 4-pin cable. _..._


My favorite is mic cable with zipcord taped to it, all crammed into 4pin connectors.


GreyWyvern said:


> ... Thanks to my upstairs comrade and occasional CB lurker GaryKuntz for posing the questions and answers.


I _KNEW_ there were more Apollo-ians here besides Kelite and you! Are Joel and Monty here incognito also? I bet they've at least peeked!


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## Pie4Weebl (Jun 25, 2010)

I'm still kind of thrown by the bins of "4 Pin Cable" next to the bins of "Color Fader Cable" at work...


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## Soxred93 (Jun 25, 2010)

derekleffew said:


> My favorite is mic cable with zipcord taped to it, all crammed into 4pin connectors.



I.... just.... wow. That's... quite scary, yet quite resourceful.


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## zmb (Jun 25, 2010)

Soxred93 said:


> I.... just.... wow. That's... quite scary, yet quite resourceful.


 
At least it's just 24V, safer than some other jerry-rigged solutions that aren't safe but work.


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## derekleffew (Jun 26, 2010)

Pie4Weebl said:


> I'm still kind of thrown by the bins of "4 Pin Cable" next to the bins of "Color Fader Cable" at work...


Tell me if I'm correct here...

Pin#......."[Apollo] 4 pin cable".............."[Morpheus] ColorFader cable"
1......... GND (-ve) 14 AWG blk................................red DATA -
2......Control data minus (-) 22 AWG red...................grn DATA+
3......Control data plus (+) 22 AWG grn.....................blk GND
4.........24 VDC (+ve) 14 AWG wht............................wht +24VDC
Chassis...Cable shield/Drain wire 24 AWG.....................case


See also this post.


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