0006 - Build a Precision Substitution Resistor for under $20.
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- Опубликовано: 12 сен 2024
- We sometimes needs precision resistor values for our electronics projects, but quality resistor substitution boxes can be expensive as can be keeping a stock of .1% resistors. However, a high precision substitution box can be built small change for those that only need it once in a while.
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I had the exact same idea for a substitution box, though I have yet to build it. I did build a bench pot from the same 10K pot. I gave it a heavy, non-skid base and a 3" round circle, for a knob. I added a wide rubber band to the side of the knob. This gives traction, so that I can dial in a setting with just one finger. I used rather small alligator clips on the wires. It is one of my best bench tools. Kudos!
That solution sounds neat!
Thanks for the comment.
I have single ten turn pots in individual boxes. This is a very good idea to get any value, 0 to 100k, precisely.
Nice!
I like it. Thanks. I have a couple of old lab grade decade boxes from a physics lab that modernized. But they take up a big chunk of my bench work space. I have a handful of .01% and .005% resistors of various values, but they are seldom the values I need. I also have a box of precision wire-wound pots that I didn't have any special use for. So I have everything I need for this project, and I can compare it against the big resistor reference boxes. In fact, I think I'll build 2, since there is often a need for a pair of matched values. Again, thanks.
I use grounding strips from home circuit-breaker boxes as bus bars on my bench since they have all of the screws on them for that purpose, and junk ones from old breaker boxes are essentially free.
Good luck with the project. They are indeed handy.
I forgot to mention a DIY bus bar... Very handy for making multiple connections. I have one, but I want to improve it. Presently, I have just one, narrow, solid-core wire, on a block of wood, with attachment wires, which have alligator clips. I intended it as a ground bar (hence the alligator clip to attach it to GND/chassis) and it has been very handy for that purpose. The solid-core wire is bent in a "U" shape and the ends are glued into the block. I will improve this by 1) having multiple separate bar blocks 2) have each bar on a jumper - this will allow a DMM to be inserted to take current readings [my brother's idea = kudos to him] 3) add an output switch to each rail to be able to take that rail out of the circuit... I guess the switch could be on the input-side of the rail. Which would you suggest and why? Well, you could just turn the bar 180* to make the switch on the input, or output. But, still, the question remains as to the better side. I am sure it is contingent upon the rig's configuration. Please and thank you. Sorry that this is written poorly; I am in pain. But, you get the idea. Art Linkletter said getting old ain't for sissies.
Sounds very interesting. Maybe make a short video of it?
So do a video on it and let us know when you do. Anyway I don't entirely get it's use. What is it for?
@@cranegantry868 I am not set up for making videos, any longer. Sorry. The bus bar is for making multiple probe connections to a common test point - Ground is a very typical connection, of course. I find trying to make even a few probe connections on the same test point within the DUT case to be tedious. Using a bus bar makes things more convenient. It is little more than a strip of small gauge wire that will accept probe hooks, having a length of flexible wire and alligator clip soldered to it and a base to stabilize it. HTH. Thank you for your interest and question.
This assumes that your DMM is correct.
You're basically turning knobs until you see the number you want
if it was a precision resistor box you could set it to precision from the numbers on the POT's
Thanks for the comment Martin.
Yes, it's as precise as your DMM. The idea is, you can get in the ball park with the dials, then you put it in circuit and fine tune it for best results, then use your DMM to find out what that value is. In my case, that's within 0.0005% for a meter that cosst less than $500. You can't get a 0.0005% decade resistor box for $500. It seems weird, but it's true.
I did see a used one on ebay recently for $1000.
@@uni-byte
No... I Understand... So did i
When i was searching this i was searching for a precision resistor box
and the key component of it would be
- You could use the POT's to dial in your value
- You'd be able to select the value without needing to use a DMM
Obviously there is a time and a place for something like this
but.... It does require your DMM to be precise
or.. I suppose you could use multiple DMM's to confirm
but again, i was looking for something that would dial in the value without the need to use a DMM to check the value before it's use
Any idea's
@@martinkuliza The only thing I can think of would be a decade resistance box. What precision do you need? That will be the determining factor.
BTW, I usually just dial in the value from the knobs before attaching it. It's not until I've fine tuned it do I use the DMM.
@@uni-byte
i was actually thinking about that.... (The Knobs)
i was wondering are they accurate, then i thought to myself,
i can just turn them and mark it wherever i want to signify what value is what (irrespective of whether the markings are equally spaced or not) or whether the knobs are accurate to the pots
as for accuracy, anything from 0.1% to 1% should be fine
don't need anything as accurate as 0.01%
@@martinkuliza The knobs are pretty accurate. Once calibrated 1% should not be an issue. I recently found a used Cenco 82817-04 decade resistance box on ebay for about $30US. It has .3% resistors in it. Maybe something like that?
I like DIY projects
I agree. They are a great pass time, give you fantastic skills practice and the opportunity to learn. On top of all that you usually end up with a useful instrument/toy you can take pride in. Not much downside.
@@uni-byte My very best wishes for you channel
@@dextertech6570 Thanks!
Good idea !
Thanks!
You get less smoke by omitting the 100R pot & fit a 2w 100R resistor .
But it messes up the precision a bit …...
Yeah, agreed. A little restraint doesn't hurt either...
But that is precision smoke!
are those knob markings accurate when paired with those pots?
Sort of. The most significant is pretty close, the other two, you need to multiply by 2 as the pots are 5-turn and the knobs are 10. Keeping that in mind, you can get pretty close. 10-turn pots for all 3 would have been best though.
Very nice Channel! Good Content u produce!
Thank you very much!
@@uni-byte You are welcome! :-)
I do not understand the point of the dials??? You have 10/5 turn pots and a DMM, the dials mean nothing.
The dials let you get pretty close. Sometimes that is all I need when very high accuracy is not required. Plus, they look pretty good in a "form follows function" sort of way. I guess I could just have a bunch of pots all wired up in a pile. But...
The dials are to make it look special.
@@cranegantry868 That too.