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mcenhillk
PostPosted: Dec 01, 2007 - 04:19 PM
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Joined: Jan 17, 2007
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Ok, so I know I am new at the hardware side of things but this one makes NO sense to me.

A buddy of mine at work insisted that they make 0 ohm resistors. I said "Of course they do. It is called wire and in comes in many sizes and colors." Then he pulls out the digikey catalog and shows me! He didn't know why and I can see why someone would spend almost a dollar on a 50mm length of wire when you can buy a 30m spool of 22 gauge for $15.

http://dkc3.digikey.com/PDF/T073/P1678.pdf

There has to be a reason someone would go the the expense of manufacturing these things. What am I missing?

I don't mind loosing beer bets (as I did on this) but there is NO WAY an entire industry is conspiring against me.

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Plons
PostPosted: Dec 01, 2007 - 04:40 PM
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Since 0 Ohm resistors look the same as its resistive brothers, it can be treated the same way in f.i. automatic insertion machines for PCB-manufacturing.

In SMT they are commonly used to let tracks on one side of the PCB cross: the second track goes between the 2 pads of the smd-resistor of 0 Ohm

Third reason is to use them as configuration resistors. (Have a look at the schematic of the Butterfly: you'll find several of these 0 Ohm resistors)

So yes, you'll have to buy him a beer. Cheers !

Nard

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ossi
PostPosted: Dec 01, 2007 - 05:00 PM
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This reminds me on a tube I once saw in a tube-museum.
They had lots of diodes,triodes, tetrodes,pentodes and
so on, but the exhibition also showed a Nullode, a
tube with NULL (=zero) electrodes. I think I was
disturbed the same way you have been about 0-Ohm
resistors.

But there is an explanation. As often, Google knows
the answer also !
 
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microcarl
PostPosted: Dec 01, 2007 - 08:25 PM
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Well, consider that you have a PCB with options. Say you remove or add options. The "Zero Ohm " may be used to enable an input that would otherwise be inhibited, with out the "Zero Ohm " resistor to pull that input to VCC or GND.

In my serial backpack, I use "Zero Ohm " resistors s jumpers to set the BAUD rate to 115.2K BAUD as the default when it is shipped. If the end user wants one of the other three available BAUD rate, one or both of the "Zero Ohm " jumpers are removed. The internal pull up resistors take care of the reset.

It so happens that I primarily make single sided PCBs for most of my projects. "Zero Ohm " resistors are great for use as jumpers, eliminating the need to drill holes and insert "Thru-Hole " jumpers.

Handy devices, they are - "Zero Ohm " resistors...

Also, several months ago, there was a thread where, the exact same question about "Zero Ohm " resistors was asked. You might do a forum search or Google search and see what turns up.

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kmr
PostPosted: Dec 01, 2007 - 09:48 PM
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microcarl wrote:
In my serial backpack, I use "Zero Ohm " resistors s jumpers to set the BAUD rate to 115.2K BAUD as the default when it is shipped. If the end user wants one of the other three available BAUD rate, one or both of the "Zero Ohm " jumpers are removed. The internal pull up resistors take care of the reset.
That works very well in your serial backpack. I've been greatly enjoying the serial backpacks I got from you and am preparing to soon post a review of your fine project.

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clpalmer
PostPosted: Dec 02, 2007 - 05:27 AM
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Joined: Oct 26, 2006
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We use lots of 0 Ohm resistors in our prototype cel phone designs at work. Since things are in the early prototype phase, there's often several possible configurations. Since it's very expensive to set up and run a PCB build, 0 Ohms are often placed around to allow for multiple configurations. Connect something one way and if you want to test the other way, populate a few and remove a few and you have the other configuration.

Don't worry, though, caught me by surprise a bit when I first saw them, too =)

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Psychlow
PostPosted: Dec 03, 2007 - 05:09 PM
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Yeah, it seems to me that they would just be used in cases where it's impracticable or undesirable to solder a jumper wire when you can cross a PCB route with an SMD device (that can be used by an auto-pickup and batch soldered.)

If there's 0-ohm thru-hole versions though, that would not make much sense to me...
 
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Plons
PostPosted: Dec 03, 2007 - 05:13 PM
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Quote:
If there's 0-ohm thru-hole versions though, that would not make much sense to me...
See my first post in this thread Smile

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Psychlow
PostPosted: Dec 03, 2007 - 05:32 PM
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Yep. Smile
And clpalmer beat me to the other thing I was going to say too, so yeah, I got to this thread way too late.
 
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microcarl
PostPosted: Dec 03, 2007 - 09:23 PM
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Psychlow wrote:
If there's 0-ohm thru-hole versions though, that would not make much sense to me...

Then you haven't done much PCB layout using thru-hole components. If making single sided PCBs, thru-hole "Zero Onm " resistors are essential - especially when the PCB is stuffed via "Auto Insertion " equipment.

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jgmdesign
PostPosted: Dec 03, 2007 - 10:31 PM
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Incidentally, zero-ohm resistors are anything but. I remembera buddy of mine used one in a pinch to create a low current ammeter. I must say it worked rather well too.

Jim

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microcarl
PostPosted: Dec 03, 2007 - 10:47 PM
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jgmdesign wrote:
Incidentally, zero-ohm resistors are anything but. I remembera buddy of mine used one in a pinch to create a low current ammeter. I must say it worked rather well too.

Jim


Very true! They can range from a few milli-Ohms to nearly an 1ohm. But they aren't tested for any particular range of values, though...

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Psychlow
PostPosted: Dec 04, 2007 - 03:11 PM
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Joined: Mar 01, 2005
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microcarl wrote:
Then you haven't done much PCB layout using thru-hole components. If making single sided PCBs, thru-hole "Zero Onm " resistors are essential - especially when the PCB is stuffed via "Auto Insertion " equipment.


I've done plenty of single-sided PCBs, but always home made and no auto-insertion equipment.

I'm not understanding something key, I guess - Why can't the equipment just be set up to insert a length of jumper wire?
 
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Plons
PostPosted: Dec 04, 2007 - 04:12 PM
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See the picture for how resistors get fed into the automatic insertion machine.
It takes one tool for all resistors of a certain wattage and such.
For wire-bridges, a special tool would be required to handle those: so ONE tool for ONE specific component. See the cost-issue ? And extra labour it would take ?
And for that same reason, packages of IC's are standarized.

Nard

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Psychlow
PostPosted: Dec 04, 2007 - 05:10 PM
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That does make sense. The automatic insertion machines I've seen have been able to insert these though:


Just depends on the machine then, I suppose. Smile
 
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jgmdesign
PostPosted: Dec 04, 2007 - 06:47 PM
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I think you took that from your toy tank. Now, go put it back. Wink

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TMBartman
PostPosted: Dec 05, 2007 - 02:12 PM
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They also make DED's or Dark Emitting Diodes.
 
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ikletti
PostPosted: Dec 05, 2007 - 04:21 PM
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TMBartman wrote:
They also make DED's or Dark Emitting Diodes.

You mean we could use them to save the universe?

Mankind 'shortening the universe's life' (Telegraph)
http://ars.userfriendly.org/cartoons/?id=20071203
 
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John_A_Brown
PostPosted: Dec 05, 2007 - 04:54 PM
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jgmdesign wrote:
Incidentally, zero-ohm resistors are anything but. I remembera buddy of mine used one in a pinch to create a low current ammeter. I must say it worked rather well too.

Jim

It probably depends on the tolerance. I always pay that little bit extra for 1% 0 Ohm resistors.
[Edit]Although, strangely, they always seem to be over 0 Ohms, I've hardly ever had one that's under...[/Edit]
 
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JohanEkdahl
PostPosted: Dec 05, 2007 - 07:03 PM
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Mr John A Brown! After a realy shitty day you saved it all with your post! Still laughing!
 
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