Author Topic: Yet another resistance decade box  (Read 52639 times)

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Offline linux-works

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Re: Yet another resistance decade box
« Reply #75 on: June 18, 2016, 12:32:32 AM »
how are the switches going to be mounted?  I don't have mine yet (on the way in the mail) but its not obvious how they securely mount.  is there a rod that would go thru them all, side to side?  I think I've seen TW switches with holes like that before.

the neat thing about lasercut boxes is that you can make them custom to-size, and since there is probably a square corner style hole to be cut, that's not something I would want to do at home with hand tools, for example.  round holes, sure, I won't invoke a laser for that.  this isn't round holes and so I'd hate to have to machine a pre-made box; might as well just blast the whole thing out on a laser and have it be exactly what you want.
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #76 on: June 18, 2016, 03:25:13 AM »
That laser-cut box looks good. I like the way the top and bottom panels overhang with the tabs inset. I suppose there could be a group buy on such an enclosure as well.

Thanks for the link to the box designer.
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Offline linux-works

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Re: Yet another resistance decade box
« Reply #77 on: June 18, 2016, 01:34:52 PM »
if enough people like a design, I could run off a small bunch of them during some scheduled time at my hackerspace.  the design would be in .pdf format so any art tool should be able to import it and edit it for re-print (re-burn?)

I'm still wondering HOW this is going to mount!?

before boards are sent out (have they been?) - has thought been given to how to mount this, remove sections for fixing or update or replacement and so on?

would it make sense to have the pcb's terminate in a finger backplane (think: pci cards and slots, etc) or something, that would help the whole thing mount?  maybe a backplane board with sockets and the rotary switches would plug into that?

if these become 'plugins', then some plastic box around that could be made to guide the modules into a backplane.

what do you guys think?

at any rate, there has to be some thought as to how these get mounted ;)
« Last Edit: June 18, 2016, 01:36:25 PM by linux-works »
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #78 on: June 19, 2016, 04:21:14 AM »
Very good points. I haven't thought about it. However, I'm awaiting arrival of an IET decade box and will see what they did. Based on the service manual, they only use five resistors per decade (e.g., for 1 - 9 Ohm decade: 1 x 1 Ohm, 4 x 2 Ohm), having the thumb wheel route current through the appropriate combinations.

I kind of like the enclosure of the RBOX Mini. It's very much in the spirit of the method you described, but with the standoffs on the outside. Using a two-layer, white and black, acrylic would make for nice etched lettering, but I suppose you'd also see the layers along the cut edge of the panel.
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Online PeterZ

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Re: Yet another resistance decade box
« Reply #79 on: June 19, 2016, 05:07:37 AM »
Normally, if you buy these switches from any large supplier, like Digikey or Mouser, at a different prices of course, they come with two ending caps having a snap in function (see the pic). No idea if you can get them for KM2 switches.
I used a high quality hot snot in my box ;)
Wouldn't adding more finger type springy contacts significantly increase the overall residue resistance?


 
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #80 on: June 19, 2016, 01:55:08 PM »
High-quality hot snot. Infinitely configurable.
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Offline m100

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Re: Yet another resistance decade box
« Reply #81 on: June 21, 2016, 12:44:17 AM »
Normally, if you buy these switches from any large supplier, like Digikey or Mouser, at a different prices of course, they come with two ending caps having a snap in function (see the pic). No idea if you can get them for KM2 switches.

Never seen them myself, are these 'KM2' switches actually a knockoff of another manufacturers part? 
The only time I've ever used these dirt cheap far eastern sourced switches they were wrapped in black insulation tape and not even fitted to a panel.   :D

 

Offline linux-works

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Re: Yet another resistance decade box
« Reply #82 on: June 21, 2016, 01:19:50 AM »
High-quality hot snot. Infinitely configurable.

for a midnight build, if a deadline is tomorrow - yes.

for a real build, I'd prefer to find something that was clean enough so that you are proud enough of the insides that you'd build it with a clear front (or all clear) panel.

also, glue is less repairable; meaning that if I needed to pull things apart and clean contacts or fix things, I don't want to deal with a previous glue job.

btw, my set of switches from ebay is due for delivery today.  I'll give mine a look and see if there is a non-glue (lol) solution to mount this acceptably.

I don't have the boards yet, but I'll see if I can do a dry fit into some plastic lasercut box and see how it goes.  when I get laser time, I'll make something and post an update.
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #83 on: June 21, 2016, 03:38:41 AM »
Yeah, I was being facetious on the hot snot. Looking forward to your impressions on the switches you receive.
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Offline linux-works

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Re: Yet another resistance decade box
« Reply #84 on: June 21, 2016, 04:49:52 AM »
I use plenty of hotmelt glue, but only on things that I don't plan to show to anyone or things that are temporary.

perfect use-case: some diy perf board with standoffs; and I'm still working on it and need some chassis just to hold the jacks up.  I'll hotmelt the alum or nylon standoffs to the chassis (pcb is screwed to the standoffs, first) and that will let me try out a wiring config or routing.  I might change a few more things over time before I want to commit to an expensive metal chassis (that someone else makes, at high cost to me).  I can pull up hotmelted riser posts easily, yet they stay down long as I need them to, to run test wires to.  as long as I don't ship it, I can even bring temp work to demo events and shows.  you'd never have a clear cover over such things, though ;)

the procedure is quick, too; with the pcb screwed to 4 alum/etc posts, dab some hotmelt quickly on the screw areas of the bottom posts and quickly position to the plastic base/box.  it sets in under a minute.  requires just hand force to pull up when you are ready to change a config or try some other board in that place.

anyway, I'd like to see something that is held down by screws or a pressure plate that pushes something against the front panel, so that its undo-able, for future service.

if people have ideas, post them!  this is not my specialty, so if others have better ideas, lets hear them.
 

Offline linux-works

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Re: Yet another resistance decade box
« Reply #85 on: June 21, 2016, 04:54:33 AM »
Normally, if you buy these switches from any large supplier, like Digikey or Mouser, at a different prices of course, they come with two ending caps having a snap in function (see the pic). No idea if you can get them for KM2 switches.
I used a high quality hot snot in my box ;)
Wouldn't adding more finger type springy contacts significantly increase the overall residue resistance?

if those fingers are the ones I've seen before, such as on IEC inlets on those snap-in power jacks, that works great for stiff strong sheet metal that is thin.  it does not work well at all on thicker plastic that isn't so strong.  with plastic, I tend to use 1/8" (common, cheap, easy/fast to cut, strong enough for most things).  you can go thinner than that but you don't get stronger that way ;)  polycarb would be thin and strong but I don't have laser privs that cut such poisonous stuff as lexan/polycarb.

I wonder if a hybrid would even be possible; a metal front panel (simple, cheap, strong) and the rest would be plastic to save weight and mostly cost.

otoh, if you go to that much trouble, maybe going all metal is the way to go.  going all metal would be more durable and also give the chance for some level of shielding, such that it is.
 

Offline linux-works

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Re: Yet another resistance decade box
« Reply #86 on: June 21, 2016, 04:56:55 AM »
I have to ask....

so, when is the automated SCPI controlled version going to come along?

LOL

(half serious, though)
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #87 on: June 21, 2016, 07:05:25 AM »
Yeah, I was half-seriously thinking about something like that. Would you switch in the resistors electronically, electro-mechanically, or go all out and rotate the switches with servos (not too practical, but cool looking)?
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Offline linux-works

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Re: Yet another resistance decade box
« Reply #88 on: June 22, 2016, 05:19:56 AM »
these things are too small!  are you guys SURE you want to work at this size?

they make larger style thumbwheels.  I really wonder if people are going to be able to do this mod..

first, removing the pcb from the switch seems mostly destructive, in that you have to cut or unweld a few plastic posts.  it can't easily be redone, either.  how are the new pcb's going to be glued or connected to the switch again?  there is no ability to use screws or anything like that.

fwiw, the unit I got did have 2 end caps with those finger stock things but that really is not going to give a reliable mount, imho.

my gut feeling - fwiw - is that it would be better to have the switches send signals to a cpu and have that controller drive a bunch of low-R contact relays with precision resistors.

don't know; now that I see this thumbwheel unit, it does not long strong or robust or worth hacking.  maybe I'm wrong, but it seems like - once you open it - its never going back together again.

we want something that will work and be trustable, right?  I guess more people have to get this and open them and then we'll get some opinions.  right now, I'm not all that hot on this particular thumbwheel.  its just too small and fragile for anything close to metrology, even DIY level.

 

Online PeterZ

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Re: Yet another resistance decade box
« Reply #89 on: June 22, 2016, 06:22:50 AM »
I think you haven't read my very first post in this thread. The whole idea of this hack was to pimp up a cheap Chinese thumbwheel switches from ebay (i guess they are a knock off of some brand, what else?) which otherwise i would thrash and generate more e-waste, definitely it wasn't to build the worlds best piece of art resistance decade box.
Thanks to Dave, the idea evolved into making a make-before-break version, which in my opinion made this hack even mode useful.
I also mentioned the size of the switches, i don't understand how it comes as surprise to you now.

Removing the pcb from the switch requires to cut off three posts, but the new pcb, once pushed in sits tight. Definitely not going to come off due to the force generated by the spring contact. If that's not enough, a very tiny drop of gel superglue will secure the spots.

I have built two decade boxes using these modded switches now, they work ok. Maybe they won't last forever, but for the price - that's ok.

If you prefer to make a relay based, mcu controlled decade box, which you can be proud of, there is no point in modding these switches. There is no point in using them at all.
This is a quickie project using cheap parts with the intention to make the best out of them.
 

Online Fortran

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Re: Yet another resistance decade box
« Reply #90 on: June 22, 2016, 09:13:25 AM »
I second what Peter said.

It's never going to be a high-end product. But with a new board it's probably good enough for most hobbyists.
It will definitely be good enough for most beginners!
And for the price of 1USD for 6 boards, complaints isn't an option.

I've poured a few hundred bucks into this already just because I like the idea, with basically zero margin. If I don't sell enough of them I'll loose money.
If you want a professional device, spend the extra 500USD or so and get one.
This is basically putting makeup on a pig, and should be treated as such.

But for what you're paying.. it's quite an attractive pig :)

 

Offline m100

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Re: Yet another resistance decade box
« Reply #91 on: June 23, 2016, 04:36:47 AM »

they make larger style thumbwheels.

Indeed they do, but ten KM2 switches cost me about GBP 4 delivered.  Larger switches from recognised suppliers and distributed by Farnell in the UK are around GBP 20 each

http://uk.farnell.com/crouzet-automation/84210054/switch-decade/dp/143617

At GBP 120 just for switches on a six decade box such a project would be a non starter for me especially when I could buy a significantly larger form factor one fully assembled and off the shelf for GBP 100

http://uk.rs-online.com/web/p/decade-boxes/3826439/

or for those with much deeper pockets an IET Labs one for GBP 600

http://uk.farnell.com/iet-labs/rs-200w/resistance-decade-box-0-99999999/dp/9769765


or a Time Electronics one for roughly the same GBP 600

http://uk.farnell.com/time-electronics/1040/resistance-box/dp/5058284



« Last Edit: June 23, 2016, 04:59:51 AM by m100 »
 

Offline linux-works

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Re: Yet another resistance decade box
« Reply #92 on: June 23, 2016, 05:09:33 AM »
I understand the original motivation and yes, after 4 pages and talk of group buys, its gone beyond one guy who has a surplus of parts he wanted to get use out of.

that said, if people have put money in, it would not be fair to leave them; and so I would continue to support the project and buy my reserved boards so that the organizers don't lose money.

 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #93 on: June 23, 2016, 01:14:13 PM »
Yep, I like this little one because the size and cost are good for tinkering. I got a used IET box for long-term, "serious" use (and higher wattage). It's all good.
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Offline all_repair

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Re: Yet another resistance decade box
« Reply #94 on: June 23, 2016, 03:44:12 PM »
I am going to throw a few into my site-work bag, and a few in the lab when testing some process meter.  Save me finding, filing or buying loose resistors for setup need.  Yes, I do have a tank-like decade box.
 

Online Fortran

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Re: Yet another resistance decade box
« Reply #95 on: June 25, 2016, 05:33:12 PM »
The boards have been shipped and should arrive in 1-2 weeks.
And the resistors have been ordered and should arrive in about a week.

So we're getting close  :-+
 

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #96 on: June 26, 2016, 08:34:29 AM »
Thanks for the update. Looking forward to it.

My IET boxes arrived. Unfortunately, they didn't go unmolested during their former lives, so I've got another project for my queue.
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Offline ez24

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Re: Yet another resistance decade box
« Reply #97 on: June 26, 2016, 10:55:48 AM »
Just read this and at 98 posts I am not 100% sure what is going on. 

I think this is a project taking some cheap ebay thumbwheel switches, cutting the guts out and gluing in some custom boards someone is making to make a decade box.

If I am right I am also interested in buying some

Maybe helpful to summarize what is going on in the 100th post.

thanks

Offline bitseeker

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Re: Yet another resistance decade box
« Reply #98 on: June 26, 2016, 02:00:05 PM »
Unless someone beats me to it, this is only post 99 (reply 98), but here's a quick summary:

   You are correct.

And a slightly longer summary:

   6x inexpensive thumbwheel switches from China
+ 6x custom make-before-break PCBs
+ 54x 1%, 1/4 Watt SMD resistors
+ 1x enclosure of your wildest dreams
---------------------------------------------------------
= Fun little six-decade resistor box
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Offline ez24

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Re: Yet another resistance decade box
« Reply #99 on: June 26, 2016, 02:23:09 PM »
Quote
54x 1%, 1/4 Watt SMD resistors

54x  whew !   What size?

Could a learner solder them?  I finished a SMD practice board, cannot remember how many components it was.  If 0402 (metric  .1mm - smaller than a baby flea), I probably could not do them.  If 6332 (metric - 1 cm) probably can  :-DD

Just curious - what is the normal way to spec these  - metric or imperial ?

thanks


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