Electronics > Projects, Designs, and Technical Stuff
Yet another resistance decade box
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linux-works:

--- Quote from: PeterZ on June 18, 2016, 07:07:37 pm ---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?

--- End quote ---

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.
linux-works:
I have to ask....

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

LOL

(half serious, though)
bitseeker:
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)?
linux-works:
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.

PeterZ:
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.
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