Author Topic: Smallest Footprint Resistor  (Read 533 times)

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Jesse6669

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Smallest Footprint Resistor
« on: August 26, 2023, 09:22:07 AM »
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I'm trying to wire up a T-scale F-unit with an 0201 LED for the headlight, and have the placement of the LED worked out, but the resistor takes up a relatively huge amount of space.  Are there any smaller footprint resistors than the typical carbon film/ceramic resistors?  Suggestions?   It really needs a resistor even though operating voltage is 3-4v-- otherwise it's way too bright..

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Steveruger45

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Re: Smallest Footprint Resistor
« Reply #1 on: August 26, 2023, 09:43:56 AM »
+1
use smd resistors.  Here is a link that you might find interesting.
https://www.ultralibrarian.com/2020/06/02/0402-package-footprint-resistor-sizes-and-parameters-ulc
Steve

peteski

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Re: Smallest Footprint Resistor
« Reply #2 on: August 26, 2023, 09:57:22 AM »
+1
Yes, even in N scale I extensively use SMD resistors. I  often etch custom PC boards to hold them, but leads can be added to them too.  IN your install I would probably use enameled magnet wire (like you already use) instead of standard insulated wires as the wire is much thinner.

Here is a SMD resistor with added wire leads (and heat shrink to protect it). Heat shrink is rather bulky. Instead you could probably coat the resistor with some liquid electrical tape sold in the electrical department of any hardware store.



And SMD resistors on a custom made PC board.



The SMD component designations actually indicate their footprint.



For example a footprint of a 0805 (Imperial  code) component (LED, resistor, capacitor) is 0.080" x 0.050".  This applies to other sizes too. So if a component is 0603, split that into halves (06 and 03) and those are the dimenstions in hundreds or inch.  0603 component footprint is 0.060" x 0.030".

The resistor size is also related to its power dissipation rating. In your case using 0805 or even 0603 size resistors would work.


« Last Edit: August 26, 2023, 10:02:04 AM by peteski »
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Jesse6669

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Re: Smallest Footprint Resistor
« Reply #3 on: August 26, 2023, 09:59:50 AM »
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Excellent--thank you (both)!

peteski

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Re: Smallest Footprint Resistor
« Reply #4 on: August 26, 2023, 10:02:38 AM »
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Excellent--thank you (both)!

I added some info to my previous post.
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GGNInNScale

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Re: Smallest Footprint Resistor
« Reply #5 on: September 23, 2023, 04:45:11 PM »
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I also use surface mount resistors and caps for small work.  Also, you can use really tiny LEDS (like 0204- only pin dots in the packages.  I use single strands of bare wire pulled from a 20 gauge stranded wire.  I put the LED on double sided tape, then take a the wire and put a small 90 degree bend in it.  Tin the bent end.  Then take the wire in a tweezer (a reverse acting tweezer works best for me).  Then heat the wire about 3-5mm up from the bend.  This will melt the solder.  Touch the bent wire to the solder pad on the LED and it will make an instant joint.  You can insulate with shrink tubing, or insulating paint.

peteski

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Re: Smallest Footprint Resistor
« Reply #6 on: September 25, 2023, 12:28:12 AM »
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Also, you can use really tiny LEDS (like 0204- only pin dots in the packages. 

I suspect  you meant 0402 (or 0201?) size LED.  Most popular small sizes are 0805, 0603, 0402, and 0201.
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GGNInNScale

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Re: Smallest Footprint Resistor
« Reply #7 on: September 28, 2023, 01:12:47 PM »
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Oops, typo...  :D