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Decade Substitution Boxes-Do you actually use them?

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FenderBender:
I have a full pallet of stuff to do this summer, electronics and non-electronics stuff...one of those things was to make resistance and capacitance substitution boxes.

Do you guys find yourselves actually using your boxes? Or perhaps the better question would be, is it worth spending the ~$50 on parts for one of these boxes, in terms of actual use?

I could see where they might be useful. Tweaking a value up or down and see how the circuit behaves, perhaps while you view some sort of meter or scope. I'm not sure if the whole 'precision' box is necessary. Since these are most likely used while prototyping, there's already a lot of uncertainties and variables in prototyping. Stray capacitance, inductance or resistance in the breadboard or your wiring. That's not to say that you should use 10% resistors, but you don't have to go mad buying 0.01% Caddocks for your box.

Sorry bit of a tangent there...But anyway. What's your opinions on actual use. I think they are 'cool to have', just not sure if its worth my time and money.

Post away...if you want.

vk6zgo:
These "precision" boxes are really only useful with DC & quite low frequency circuits.
The connecting leads add stray capacitance & inductance,even when the internal circuitry is designed to minimise strays.
Most substitution boxes sit in the corner of the shelf gathering dust.because of these considerations.

Re your "tangent":It has always been my understanding that the essence of good design is to make things which will operate within specifications using normally available standard tolerance components.
Neither active devices,or other passive components are specified to such close tolerances as resistors are.

Another point to consider,is that "close tolerance" resistors are not necessarily "high stability"components.
In many,probably most,cases they are,but not universally,so it may sometimes be better to choose,say,a 1 % tolerance "high stab",which still maintains that degree of tolerance in 10 years,than a 0.1% tolerance resistor which changes value with age.

FenderBender:
Right. Well I put 'Caddocks' as I am fairly sure they are very stable with temperature and over time. Just an example.

I wonder if you made a few substitution boxes if you could avoid having to stocking resistors at home! :P Just dial it in.

Well as I said, I think they are interesting, but I'm not sure how useful.If I was to use one, I don't think I would be using it to tweak a circuit. Like instead of using a standard 470Ohm resistor, I dial in 471.7Ohms. In the real world, a resistor with such a resistance would be hard to find and probably expensive. Rather just changing resistor values to see how a circuit responds. Not for actual "tuning".

Yeah I probably not making sense.

vk6zgo:
One way of looking at it is,if you make or buy some,use them for investigating the effects of changes,as you suggested,then put them on the shelf,& use them once or twice in the next few years,you have had the learning experience,& they will have been handy to have from time to time.

One use which comes to mind,is selecting series resistors for a maybe unknown analog milliammeter to read voltage,though that is less likely these days.
Even discovering the limitations of these devices could be a learning experience!
If you can build or buy fairly cheap,they won't owe you much,& if you find they just sit on the shelf,you can sell them on eBay.

Short Circuit:

--- Quote from: FenderBender on July 05, 2012, 03:39:13 am ---Do you guys find yourselves actually using your boxes? Or perhaps the better question would be, is it worth spending the ~$50 on parts for one of these boxes, in terms of actual use?

--- End quote ---
I have been in electronics for some 25 years, 12 of which making a living out of it.
Don't recall ever having wanted to have one of these at hand. So waste of time and money imho.

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