Author Topic: Yet another resistance decade box  (Read 52677 times)

0 Members and 1 Guest are viewing this topic.

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Yet another resistance decade box
« on: May 16, 2016, 09:50:12 PM »
I got some of these cheap thumb wheel switches (smaller ones, ~18mm height) recently.
Unfortunately, the overall quality and the drilling precision, as you can see on the attached picture, may occasionally lead to increased contact resistance. Pretty significant increase ;)
Since it is a PCB, i decided i'll make a new one, 0.6mm thick, easy to cut and trim with scissors, already accommodating footprints for one decade of 1206 resistors.
The small jumpers near the terminals pads allow to configure them as input or output. Makes the wiring easier:
Code: [Select]
     1R  10R 100R 1k
out---+   +---+   +--- ... +
      |   |   |   |        |
      +---+   +---+        +--- in

The PCB with 6 such modules is smaller than 5x5cm. I designed it using SprintLayout6.

Design files (gerbers for 1206, 0805 version and the original SprintLayout project) are HERE (github repo).
 
The following users thanked this post: kripton2035, bitseeker, meandeev, anfang

Offline Dave

  • Super Contributor
  • ***
  • Posts: 1058
  • Country: si
  • I like to measure things.
Re: Yet another resistance decade box
« Reply #1 on: May 16, 2016, 09:56:05 PM »
Pretty clever idea. :-+
What sort of resistance are you getting on zero setting?
<fellbuendel> it's arduino, you're not supposed to know anything about what you're doing
<fellbuendel> if you knew, you wouldn't be using it
 
The following users thanked this post: meandeev

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #2 on: May 16, 2016, 10:10:40 PM »
Thanks! :) Using 4 wire method on my 3456A the measured resistance on 0 setting is about 60 mOhm.
I didn't bother to order these PCBs with gold plated pads, it's just a standard lead free HASL.
 

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #3 on: May 16, 2016, 10:27:12 PM »
Clever indeed.  :-+
Do they still stack together despite the added height of 1206?
I might steal this idea and make a larger batch with ENIG.
 

Offline matseng

  • Frequent Contributor
  • **
  • Posts: 515
  • Country: my
    • My Github
Re: Yet another resistance decade box
« Reply #4 on: May 16, 2016, 10:38:05 PM »
I might steal this idea and make a larger batch with ENIG.
If you do and decide to sell some of the pcbs please sign me up for a dozen....  :-+
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #5 on: May 16, 2016, 10:46:33 PM »
Do they still stack together despite the added height of 1206?
That was my first  :palm: moment when i got the pcbs ;)
It's not perfect, but good enough (for me):
 

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #6 on: May 16, 2016, 11:28:40 PM »
I had a feeling that might happen  :)
Not a huge deal to correct though. Just make the board a bit longer.

If you want to remake them, I'll buy a dozen or two.
If not, I'll remake them as soon as I get some computer quality time. :)
 

Offline linux-works

  • Super Contributor
  • ***
  • Posts: 1867
  • Country: us
    • netstuff
Re: Yet another resistance decade box
« Reply #7 on: May 16, 2016, 11:35:07 PM »
cool idea.

I see a group-buy coming (perhaps)?

I'd grab some if there is a GB.
 

Offline Photon939

  • Regular Contributor
  • *
  • Posts: 72
  • Country: us
Re: Yet another resistance decade box
« Reply #8 on: May 16, 2016, 11:50:44 PM »
Seconded on the group buy motion  :-+
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #9 on: May 17, 2016, 12:02:16 AM »
Guys, hold on, new version in the works.
Another possible issue: do all of these switches have the same layout for mechanical holes? Probably not. First we'd had to find the source for exactly this type. Of course, if you don't want to redesign the board.
I don't think i will be ordering the new version, but will do the design/post the gerbers for you.
 

Offline Dave

  • Super Contributor
  • ***
  • Posts: 1058
  • Country: si
  • I like to measure things.
Re: Yet another resistance decade box
« Reply #10 on: May 17, 2016, 12:43:55 AM »
I see these being useful for experimenting with values for something like loop feedback adjustment and whatnot, but there is one major problem that these have. They go open circuit while you are switching a value, which could leave the loop momentarily without feedback, making it go crazy. The solution to this problem would really be quite simple, you'd just have to make sure one of the wipers hits the next contact before the other one leaves the first contact.

I sketched up something in altium that I think might work.
<fellbuendel> it's arduino, you're not supposed to know anything about what you're doing
<fellbuendel> if you knew, you wouldn't be using it
 

Offline Macbeth

  • Super Contributor
  • ***
  • Posts: 2268
  • Country: gb
Re: Yet another resistance decade box
« Reply #11 on: May 17, 2016, 12:57:58 AM »
Genius idea! I much prefer the original compact design than the longer one. Perhaps some of that spare PCB could be used to make L shaped shims for stacking them without gaps?

@Dave - Another great idea!  :-+
 

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #12 on: May 17, 2016, 01:22:42 AM »
@Peter - Well you could always post a drawing of the mechanical layout of your switches.
Anyone who has one that matches could post where they got it.

I have no problems with ordering enough of them to be able to sell for around 1USD each, with ENIG. (Board only)
Plus 2-3USD per order for shipping anywhere in the world.

Dave has an excellent point.
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #13 on: May 17, 2016, 01:52:03 AM »
@Dave - great idea! I don't have any access to altium, but i tried to "draw" something similar in Sprint Layout.
I will try to etch a test board, only one layer to see if it works.

@Fortran - i added one extra layer to the gerber files (board outline + npth holes). You can import it to your PCB software and use as a template.

 
The following users thanked this post: Priestblood

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #14 on: May 17, 2016, 03:03:06 AM »
I made a quick drawing from the gerbers, as one would measure with calipers.
 

Offline Dave

  • Super Contributor
  • ***
  • Posts: 1058
  • Country: si
  • I like to measure things.
Re: Yet another resistance decade box
« Reply #15 on: May 17, 2016, 03:06:06 AM »
I forgot to mention that the similarity to the Aperture Laboratories logo is strictly coincidental. ;D

You could remove those direction selection jumpers on the bottom and reduce the size of the board slightly. It doesn't matter which way the current flows through a resistor.
<fellbuendel> it's arduino, you're not supposed to know anything about what you're doing
<fellbuendel> if you knew, you wouldn't be using it
 

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #16 on: May 17, 2016, 03:20:58 AM »
@Dave - In order to avoid lawsuits, this too was strictly coincidental  ;D
Made it for my nephew.  It's a "lights and sound thingamajig(tm)".
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #17 on: May 17, 2016, 08:27:40 PM »
I etched a small test pcb today to check if the make-before-break operation of the switch. I used the continuity tester to check if there is a short beep when the switch passes from one setting to another.
Result: yes, it does work.
I think i will make two versions of the board: one as in original: break-before-make and the new make-before-brake, maybe a few versions of a small 5x5cm panel (sort of), consisting MBB only, BBM only and MBB+BMM versions.
 

Online BravoV

  • Super Contributor
  • ***
  • Posts: 4218
  • Country: id
  • An EEE (Eternal Electronics Enthusiast)
Re: Yet another resistance decade box
« Reply #18 on: May 17, 2016, 10:41:11 PM »
Subbed, just in case there is a group buy, count me in.

Offline nuno

  • Frequent Contributor
  • **
  • Posts: 477
Re: Yet another resistance decade box
« Reply #19 on: May 18, 2016, 02:45:37 AM »
 :-+  :-+
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #20 on: May 18, 2016, 06:02:56 AM »
Meanwhile, i've built one decade R box using the PCBs i have and set of 1% resistors (1M, 100k, 10k, 1k, 100R, 10R):



The total resistance when all switches are set to 0 is about 370mOhm.



You could remove those direction selection jumpers on the bottom and reduce the size of the board slightly. It doesn't matter which way the current flows through a resistor.
I used these jumpers only to make the wiring easier, like this:



Removed them in the final version. The PCB size is 46.5x46mm (filled up the remaining space with an SOP/SOIC adapter, adapters are always handy).


 

Offline Dave

  • Super Contributor
  • ***
  • Posts: 1058
  • Country: si
  • I like to measure things.
Re: Yet another resistance decade box
« Reply #21 on: May 18, 2016, 08:04:20 AM »
You can still wire them the exact same way even without those jumpers. Again, they are resistors, it makes no difference which direction the current flows through them.
<fellbuendel> it's arduino, you're not supposed to know anything about what you're doing
<fellbuendel> if you knew, you wouldn't be using it
 

Offline Fortran

  • Regular Contributor
  • *
  • Posts: 183
  • Country: fi
Re: Yet another resistance decade box
« Reply #22 on: May 18, 2016, 02:56:08 PM »
Nice!  :-+
If you're making both BBM and MBB it might be a good idea to put that somewhere on the silkscreen so you don't have to take it apart to know which type it is.

For a group buy, it would be more economical to arrange them 1x6 or 2x6.
The 50x50 format is great for those who want to order themselves though.
 

Offline linux-works

  • Super Contributor
  • ***
  • Posts: 1867
  • Country: us
    • netstuff
Re: Yet another resistance decade box
« Reply #23 on: May 19, 2016, 07:42:05 AM »
even more, to differentiate, put ribbed edge or something on one but different style on the other.  something physical that you can use as a cue.  I always like seeing stuff like that.

(OT: pet peeve of mine: when you have a thruhole electrolytic and your silk symbol has the index (plus or dot or whatever) INSIDE the inscribe circle, so that once the cap is installed, you can't visually tell, easily, if its in right or reversed.  just another plus symbol added outside the cap circle would do wonders to allow desk checking.)
 

Offline PeterZ

  • Contributor
  • Posts: 47
  • Country: de
Re: Yet another resistance decade box
« Reply #24 on: May 21, 2016, 10:22:09 PM »
Okay, the github repo is updated with multiple versions of the board:
LINK
including:
  • single boards - if you'd panelize them yourself
  • about 50x50mm format - 4xMBB, 4xBMM and mixed 2xMBB+2xBMM versions and an SOP/SOIC to breadboard adapter to fill up the space
  • 1x6 MBB
  • 2x6 MBB
I made only the MBB version of the last 1x6 and 2x6 formats. I think this one will be better suited for R decade boxes.

The MBB version is not 100% verified yet. I am going to order a small set of ENIG ones and build another, more precise box with 0.1% tolerance resistors.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf