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- เผยแพร่เมื่อ 26 ต.ค. 2011
- Dave feels a tad nostalgic, so takes apart his 25+ year old DIY decade resistance substitution box. And some info on how you can build your own.
DIY thumbwheel box:
www.eevblog.com/forum/index.ph... - วิทยาศาสตร์และเทคโนโลยี
Back in the mid-70s as a teenager I once did something broadly similar: a friend who was into photography wanted a timer for his negative/print copy enlarger. It was to set time up to about one minute, with one-second resolution all the way. So I built a 555-based timer with two different trimpot banks in series, one set to 0, 10, 20, ... 50 seconds and the other to 0, 1, 2, 3... 9 seconds. Rotary knobs labeled at tens and unit seconds would add the selected trimpot values resulting in surprisingly precise timed intervals from 0 to 59 seconds, with 1-second resolution.
i love all the crazy analogies you use for different sizes of things
Knee high to a grasshopper, going all over the shop, dodgy. I ❤this dude. Keep it up bro.
What model stove did you get those knobs from? :)
A plastic box MADE IN AUSTRALIA?
Wow, when is the last time you ever saw that? Amazing.
Great video, I want to build one and you answered many of my question.
I was wanting to make one with jumpers.
Loving your lessons.
@CampKohler Yeah, I agree. The open air ones you can at least clean. The sealed ones in my unit would not be easy to clean and repair.
Gonna make one when i get a sildering iron for christmas! Awesome!
I can't believe you saved all of this "crap". Awesome.
I wish I had done the same with some of my old projects. **sigh**
Makes me want to make a decade box so much. It's pitty I don't have a use for it yet..
@laharl2k Pots are useful in some instances, but a decade box has a ton of uses.
@hitachi088 Suppose you know that you will need some 1% resistor to trim a circuit, but don't know what the value will be (can't calculate it due to unknowns, lack of knowledge, etc.) . You substitute the box for the resistor, dial it until the ckt works and replace the box with the dialed value.
A box made with cheap 5% resistors (called a resistor substitution box) can be used in the same way when you don't need the accuracy and don't want to risk damaging your expensive decade box.
I was looking up decade resistors on eBay, and now there's a couple of different boards for 7-decade ones, where they used IDE headers and jumpers on the board, and you simply put the jumper on the value you want to use. Guess it could be easily adapted to use thumbwheel or rotary switches by using a compatible connector for these headers. And they're like 5 to 15 bucks a pop, depending on the model you get, so I'd say it's worth a try at least!
neat idea, i might also make one myself.
I usualy use some of the 25 turns presets (the tiny blue ones with the golden screw), calibrate them with the multimeter and then use them. but yeah, it's way better to just dial the value in instead of having to turn everything off to change it.
plus even though they have 25 turns of precision, the low edge isn't that good so a 1KOhm pot will jump go from 24 to 0 ohm, and that can fry some stuff, the rest of the range will do 1ohm precision just fine.
Any ideas for heatsinking resistors? It might be nice to build one of these in an aluminum box and mount the resistors on the box so it can heatsink them, but how to get good thermal contact without shorting the resistors?
@hitachi088 Another use for a decade box is to act as the precision adjustable part of some measuring instrument. Many of these old-school (pre solid-state) instruments (Wheatstone bridges, etc.) had a built-in decade box, making them expensive. By moving an external box between different instruments, the instruments can be made cheaply and still have the desired accuracy.
@Deckardsvr Whenever you interpose a solid-state device between the resistors and the binding posts, the output resistance is affected by the on-resistance of the device and the device's ratings. Unless you can design some really whiz-bang circuitry that incorporates the device's characteristics with the desired accuracy, you will just be asking for problems. Using the MCU to switch some husky relays with well-maintained (cleaned) contacts could work, but that's a lot of trouble.
@zigmaex Yeah, I think I'll permanently drop the intro and music for normal videos.
The exact same bad penny screwdriver…. You crack me up man!
@aleeks831 Sure - enjoy what you do, and find time to work on your own stuff that has meaning to you.
cool, I've never seen one of these before :P. I'm an EE undergrad kind of becoming disillusioned with all the seemingly pointless work I have to do. It's gotten to the point that I'm not learning much as I'm just struggling to cram the next homework or test in.
Your videos are a great! Got any advice for a young EE in the making?
These boxes are used for systems or circuits you need to tell from on what resistance something switches, or gives a signal...
Dave, is it possible to use a rotary encoder(s)+microcontroller(arduino) to switch the restistors?because the way i think it it would be a lot cheaper and same reliability as using high quality rotary switches.
Determining resistor values experimentally and serving as oddball value resistors are some common uses.
Does it matter about temperature much if your gonna use the decade box for circuit design then install a 5% carbon film when your done?
@aparlett Digikey/Mouser/Farnell C&K and Omron would be two quality known brands.
The screwdrive has white in the bit grooves. Poking holes in dry wall?
If you are going to use inexpensive rotary switches (while not ideal as the heavy-duty monsters used in a traditional precision decade box, though still useable for bench work), it would be better to use switches with an open-air design so that you can periodically spray contact cleaner to deal with oxidation and prevent wearing of any contact plating.
@CampKohler you're right, the adding Ron would be a catastrophe especially in the lower decades, that's a shame, i thought 'why there's no digital decade box anyway ?' and the 'relays' approach as you said would be a terrible hassle, thanks for the answer.
Dick Smith! Oh wow, I started out on those kits as a kid.
I thought it over and realized that you are really using the percentage key in that calculation...never mind then. You remembered, but used a method different than I'm accustomed to.
What exactly is the purpose that the diodes serve in the projector? I ask because it sounds like the projector needs the diodes in order to work.
so if you run audio through that is it then become a equalizer?
I wonder if I can use my normally opened 5 pin binary encoded switches
There we go. My first project.
"Knee high to a grasshopper"
"Knee high to a grasshopper" is also a saying in the USA where I live, although not used much.
Same in the UK. I immediately recognised the expression, but can't remember when I last heard it used.
That's a cool decade box! Reminds me of one I made as a teen. If you need hand made Resistors, shunts, or sensors, PM me and I will send you some on the house to use in future videos. Cheers.
I have a question :
what about analog switches (like the old 4066) some modern smd models are cheap these days, i thought i could built a decade resistance controlled by an MCU with enough I/Os using 4 AN/switchs per decade using your second schematic.
it would be great to dial the desired value on a keypad :)
is there anything wrong about this approach ?
by the way, you built that one at 12 ?, very impressive!
Is that screwdriver a Turner Australia screwdriver?
wow 12 years old, nice!
actually the tolerance % will go down, because they average out, it's like taking more sample of something
Those 10 position rotary switches are a bit hard to find and also kind of expensive...
I'll build the 2nd option since I have some 4 Position DIP Switches and they're also dirt cheap.
I can also get some metal film Resistors, 0.5W and probably 1% accuracy.
I'll probably put all this together on a perfo-board / strip-board and 3D Print a case.
>MrMistery (I do not get a reply button for you for some reason)
Worst case is what tolerance is. At worst, a 1% 100 Ohms resistance will be 99 or 101 ohms. What you are talking about is what you might measure which is what the calibration sheets showed for the IET substitution box.
+SlyPearTree I still don't understand. Forgive me if I'm being thick here, but by adding uncertainties in quadrature the overall percentage that it might be off from ideal value will decrease from the original value per resistor, won't it?
In this case [ 09:50 ], uncertainties for each resistor is 100 ± 1% but when in series as drawn, it would be
[math] 100Ω + 100Ω + 100Ω +100Ω ± \sqrt{1^2 + 1^2 + 1^2} = 400Ω ± 2Ω = 400Ω ± 0.5% [/math]
am I wrong in treating them as random values?
that is some damn luck that I came back here almost half a year later.
grr, now I have to build one of these
@CampKohler Correct. "Dicky" is a slang word for something that's "a bit broken" or "playing up" etc. Dick Smith was commonly referred to as "Tricky Dick" and the store as "Tricky Dick's"
"These go to eleven."
(4:25) - The knobs on my homemade resistor box go up to eleven.
One better, right ?
>
Iam impressed that you where 12 when you built it...
I may be mistaken here; but when calculating the tolerances, isn't he taking it as worst case scenario? Wouldn't uncertainties add up as independent uncertainties in quadrature and therefore go down?
Hey dave
Could you recommended where I can get some good quality Thumb wheel Switch's from .
thanks
I found some on Adafruit and on DigiKey.
@09:30 abouts, so 4 of 1% resistors equals 1%, ok get that, but..... if you have 2 1% and 2 of 5%, then how do you work out the effective % ? is it 5%+5%+1%+1% = 12% / 4 (for 4 resistors) so 3%.... or is it more complicated ....
Nothing was said about the ratings of the resistors. Fuses could protect the Rs, but will introduce inaccurate/unstable variables. Has anyone devised a circuit that will open if the rating is exceeded, but introduce a known and stable resistance (that can be mentally subtracted while using the box)? Solid state with a reset button would be best. Maybe with a set of n.c. clean relay contacts gobbed with air-excluding silicone grease.
Wouldn't a better name for these things be "Quantized Variable Resistor" boxes, QVR boxes for short?
We have those boxes in the US too. We just don't call them jiffy boxes.
Huh, never thought of having a bunch of equal value resistors be in series like that. Shame there’s no simple shortcut like that for capacitance boxes.
You could switch each capacitor into a parallel set; very similar concept.
What exactly are the kind of switches at 7:53 called?
Thumb nail switches
But what are they for??
9:37 error resistance not found
@zigmaex I kinda liked the "drawing in" intro.
how about a long carbon rod with slider as a variable resistor
That doesn't achieve the functionality of pre-selecting a fairly precise resistance value.
Sir how to make this box
no Digital Read-Out? Shocking
Ha, "half a bee's dick". Never heard that before. Definitely using that at the first chance possible.
" Bob's your uncle" ... LOL
Actually, it is VERY unlikely for all of series resistances to be high or for all to be low; it is much more likely for some to be high and others to be low. Because of this the tolerances add in quadrature,
dR = sqrt( sum(dRi^2)) = sqrt(N) dRi
if Ri=Rj for all i, j. Or expressed as percent
dR/R = sqrt(N) dRi / (N Ri) = (dRi/Ri) (1/sqrt(N)).
The %Tolerance is lower by 1/sqrt(N).
You’d have a point if the resistors were like a random sample from some unimodal continuous distribution. But they aren’t.
Resistances in resistors you buy aren’t Gaussian distributed (not even truncated Gaussian) because they don’t come straight from the production line. They are preselected. They likely come from the same batch and the resistors are usually not centered on the nominal resistance, they are more like higher precision rejects (you’re getting say 0.5% rejects as 1%). Say an entire 1% tape may be like 0.4% high - and be matched much better, say 0.05%, within a consecutive run on the tape. It’s much worse with 5% resistors. They are the 1% discards/overruns, almost always (at least the ones I usually buy). You measure them and they measure much better than 1% between each other - because they are manufactured to 1% tolerance but were slightly out of the acceptance range. Or even maybe not rejects but 1% overstock marked and sold as 5%. Sometimes there’s not enough demand for “less popular” values so the manufacturer is free to sell them for a bit less as lower tolerance parts. Or sometimes the production line has to make runs too long for the market, so they know ahead of time that only a small part of the batch will be sold at highest tolerance. Basically the tolerance range doesn’t imply anything about distribution. If you get enough 5% of one value from a manufacturer don’t be surprised if you get a multimodal distribution, with modes around better tolerance series nominal values :)
@@absurdengineering Actually, I DO have a point; no ifs, ands, or buts. The central limit theorem from statistics supports my point. As more resistors are added in series, the resulting total resistance distribution DOES become more and more Gaussian regardless of the individual resistance value distribution.
The vast majority of commercially available resistors are manufactured to specification; this is no longer 1930. The materials are specifically designed and molded to yield the specified values and to remain within those specifications over all temperature, humidity, pressure, etc. variations typically expected from their environment.
th-cam.com/video/gFEYuaY35Vo/w-d-xo.html
In that toggle switch config... maybe using binary values is better
the only problem with that will be getting resistors of that value
It's since yesterday I'm trying to figure out what are those black and red connectors on the box called: can anybody help me out? I'm trying to find some for my own box but I don't know what they're called.
The screw terminals? They are Banana Jacks mate.
I have Brain Farts myself mate, All good.
Jesus
Those are actually called 5 way terminals. They take banana plugs, and unscrew to take bare wire, fork terminals, eye terminals, and I forget what else.
I am still using my Crescent Blade driver I bought at Sears in 1955.
What? It doesn't go to 11?
:)
+lnpilot You could build one that does.
It's possible to dial it to 11 ohms though.
+IsbjörnXII Or even 11 THOUSAND OHMS
Dekastat DS1463
Why are electronic caps polarized?
you probably meant "electrolytic" caps.
oops! your right (stupid auto-correct)
+seth altobelli
Google says "Some caps -- such as nearly all electrolytic capacitors and tantalum capacitors -- are polarized.
Such caps use some sort of chemical reaction between an anode and a
cathode made of two different kinds of materials to form a thin
insulating layer."
So basically it's polarized for the same reason batteteries are polarized, different metals reacting with an electrolyte between them. :)
+IsbjörnXII Cool!
lol "half a bee's dick". I love being Australian :)
These go to 11.
OmG you were young some time ago!? 🤔😂😂😂
That could be made in Austria :P.
That would be- made in AUT
Make one that goes to 11.
:)
Dick Smith is still around?
the store dick himself
*or dick smith*
Resistance not found anyone?
(404 R = 404 page not found)
Anyone making a box with 10% or 20% resistors for repair work should realize that a resistor maker may pull out all the 5% resisters from the 10% or 20% you might buy. So if you want 5%, buy 5%, rather hoping the other tolerances might be that close by accident.
Note that "Dick Smith" is an electronics parts shop and has nothing to do (I think) with Dave's use of the word "dicky."
Dave 0.0025% x 60% does not equal 0.15%.
The formula you want is: (R nominal/10E6) x (PPM) x (Delta Temp) which will give you the 0.15%. Just thought I would remind you, in case you have forgot how to calculate a resistor PPM/Centigrade change.
what is " bob's your uncle"???
From what I got of wikipedia, it's a British and Brit colony(Australia in this case) term, usually said after something simple is explained.
Alperen Akküncü It means 'easy as that'.
***** That would only be funny if Data said it.
@ 11:10 did you say "half a bees dick?" :)
Aussies.
Wafer would have been able to be repaired I salvage all switches from vintage equipment
The battery must be dead by now...
You made this when you were around 12 years old. And you don't know if it's 20 or 30 years old?
So you're in doubt being around 32 or 42 years old?
That sounds like you're at least 50 years old 😂😂😂
Nice piece of equipment....you too are a vermiculite!
it's a bit dicky...... ha ha ha
voice
Horrible audio