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Old 20th Jun 2020, 12:16 pm   #1
daviddeakin
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Default Resistance Decade Box

I only recently realised my old Cropico resistance box only goes up to 10k ohms, and I really need 1Meg or more. Then I saw the prices of new resistance boxes..! Luckily I had a few high quality 20-way ELMA switches, so I made this for myself. I did try to etch the front panel, but that turned out to be a massive failure, so I used printed vinyl.
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Old 20th Jun 2020, 12:49 pm   #2
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Default Re: Resistance Decade Box

Top job, very neat and tidy!
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Old 20th Jun 2020, 1:12 pm   #3
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Default Re: Resistance Decade Box

Very good I am also impressed with the front operating panel
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Old 20th Jun 2020, 6:00 pm   #4
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Default Re: Resistance Decade Box

That looks very professional to me, I love the enclosure. Well done, Dave.
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Old 21st Jun 2020, 5:57 am   #5
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Default Re: Resistance Decade Box

What a cracking job, smaller too than the other one. Big, clunking decade boxes are a pain in the bum when bench space is optimum.

"I am also impressed with the front operating panel" me too, I'm always amazed that folk have mastered PC software enough to be able to produce front panels. Labelling and front panels detail is one thing that is sadly lacking in my builds. Oh for the patience to master software and a decent printer.

Andy.
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Old 21st Jun 2020, 9:22 am   #6
Kevin Hoyland
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Default Re: Resistance Decade Box

Hello
Outstanding work and it looks the part

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Old 21st Jun 2020, 10:51 am   #7
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Default Re: Resistance Decade Box

very nice, it always annoys me slightly though when I see people who have mastered the computer to be able to make such a nice front panel.I can repair cars, I can wire up complex machinery in all sorts of places, but could I make a computer turn out something like that, could I eck as like. Some people have wonderful skills.
I'm going to make one, but it won't be as fancy as that, now where's my Dymo labeller? lol
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Old 21st Jun 2020, 5:29 pm   #8
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Default Re: Resistance Decade Box

Is that large manufactured a Cropico decade box, we had several of their products where I once worked, they oozed quality. I'm just the same as Phil above on using a computer. Ted
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Old 21st Jun 2020, 7:06 pm   #9
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Default Re: Resistance Decade Box

OK, so I'm going to buck the trend of congratulation, here. I would have thought that the Cropico (Croydon Precision Instrument Company - note "precision") decade box was probably precision resistances (0.5% or tighter) and probably non-inductive at that. I would venture that the switches were high-quality, too. If what you wanted was a resistance substitution-box, then you've made a nice job of it, but as a precision instrument, I have my doubts, unless you can inform us of the quality of the switches and resistors (none of those are cheap!).

Colin.
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Old 21st Jun 2020, 8:20 pm   #10
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Default Re: Resistance Decade Box

Nice job. What is clever, in my opinion, is using 3 switches to get 6 decades in a compact box. After all, if 1% resistors are used, there is no need for more than 3 switches. I have not seen another decade box with more than one decade on each switch.

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Old 22nd Jun 2020, 8:43 am   #11
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Default Re: Resistance Decade Box

Quote:
Originally Posted by ColinTheAmpMan1 View Post
If what you wanted was a resistance substitution-box, then you've made a nice job of it, but as a precision instrument, I have my doubts, unless you can inform us of the quality of the switches and resistors (none of those are cheap!).
The switches are ELMA type-04, gold plated, high torque. They cost about £20 each but these were removed from some old equipment. The resistors are ordinary 1% metal film. I have no need for better precision than that, since I wouldn't be using resistors that are any better in the final appliance!
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Old 22nd Jun 2020, 8:46 am   #12
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Default Re: Resistance Decade Box

Quote:
Originally Posted by Diabolical Artificer View Post
Oh for the patience to master software and a decent printer.
It's pretty easy with Inkscape (free). I get the vinyl printed by a service I found on the popular auction site.
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Old 24th Jun 2020, 12:46 pm   #13
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Default Re: Resistance Decade Box

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Originally Posted by Neutrino View Post
I have not seen another decade box with more than one decade on each switch.

David
That's probably because you might want to use more than one decade at the same time. For instance 9,999,000 ohms on a decade-box that goes up to 10 M? Ok if you only want a substitution-box and to be able to select a preferred value, but a bit of a problem if you really want to make advantage of the 1-in-1000 (0.1%) accuracy of a precision decade-box. The original manufacturers were no fools and that is why the original decade-boxes were (are?) expensive items.
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Old 24th Jun 2020, 2:19 pm   #14
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Default Re: Resistance Decade Box

The way it's done has three decades available at any one time, and as it's been built with 1% resistors, having more decades available would not just be pointless, it could also be confusing due to non-monotonicity. A nice piece of appropriate design.

David
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Old 25th Jun 2020, 8:33 am   #15
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Default Re: Resistance Decade Box

You might also notice the high-resistance ranges come first, i.e. to access the 10-ohms range I have to turn the switch through the 10k range first. That stops me from burning out the smaller resistances with excessive current. Luckily I spotted this failure mode before I printed the front panel! (quick redesign)
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Old 25th Jun 2020, 1:26 pm   #16
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Default Re: Resistance Decade Box

Quote:
Originally Posted by ColinTheAmpMan1 View Post
OK, so I'm going to buck the trend of congratulation, here. I would have thought that the Cropico (Croydon Precision Instrument Company - note "precision") decade box was probably precision resistances (0.5% or tighter) and probably non-inductive at that. I would venture that the switches were high-quality, too. If what you wanted was a resistance substitution-box, then you've made a nice job of it, but as a precision instrument, I have my doubts, unless you can inform us of the quality of the switches and resistors (none of those are cheap!).

Colin.
I'll stand up in defence. OK in the days of older boxes with precision resistors, then the value could be taken as read As all we had to check the value was an analogue meter with the accuracy as close as eyeball MK1 could get. But thse days with DVM of high accuracy, we don't really need such tolerance. Stick the box into a circuit ,twidle to get a value, and thn check the value on a DVM.
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Old 25th Jun 2020, 1:36 pm   #17
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Default Re: Resistance Decade Box

Outstanding work well done .
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Old 25th Jun 2020, 3:51 pm   #18
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Default Re: Resistance Decade Box

I might have printed the 'alternate range' upside-down so you turn the box round when you need to use the other range. Very clever design in any case!

dc
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Old 25th Jun 2020, 4:38 pm   #19
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Default Re: Resistance Decade Box

But it's not really an 'alternative range', the design is cleverer than that. You can have any 3 consecutive decades, for example the 100k (switch 2), 10k (switch 1) and 1k (switch 3), in use. So I think it makes sense to have them all reading the same way up.
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Old 26th Jun 2020, 4:32 pm   #20
ColinTheAmpMan1
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Default Re: Resistance Decade Box

Quote:
Originally Posted by daviddeakin View Post
You might also notice the high-resistance ranges come first, i.e. to access the 10-ohms range I have to turn the switch through the 10k range first. That stops me from burning out the smaller resistances with excessive current. Luckily I spotted this failure mode before I printed the front panel! (quick redesign)
OK, I can see the idea of only using 1% resistors if that is all you are interested in and the logic in arranging the orders of magnitude, but in point of fact, the higher-value resistors are the ones that get burnt-out first, because they tolerate less current than the low-resistance ranges. It sounds counter-intuitive, but if you take a look at any old decade boxes, you should notice that the current-rating of the higher resistances is much lower than the lower ones. Also, as I have already said, its the higher resistances that get burnt-out first, because users can be rather ham-fisted at times (if they had to pay for the decade-boxes, they might be a bit more careful).
I know what uses I put decade-boxes to and what I put substitution-boxes to and I have both. The OP might have some purpose for this device that he has made, but am I really the only person to think that using three high-quality, expensive switches with resistors that cost a penny or less is a bit uneconomic?

OK, yes, I probably am the only one.

Colin.
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