Resistor substitution box project - rotary switch / knob

[kripton2035]

just for the records, are you aware of this ?
http://kripton2035.free.fr/LabTools/lbt-resistordeca.html

[Analog Kid]

just for the records, are you aware of this ?
http://kripton2035.free.fr/LabTools/lbt-resistordeca.html

Now that is definitely cool. (Decade box using cheap thumbwheel switches.)

[tggzzz]

And to be honest, i don’t think that this projects are a waste of money and time, as i learn how to calculate components values, order the components, design the pcb, and i will also test the projects. As for the money, there are not many components that i have bought for this projects.

Just so. Listen to others, but do what is right for you.

As for choosing switches, yes there is a bewildering choice - and it leads to a phenomenon known as "paralysis by analysis". That's true of many components and even everyday life, e.g. supermarkets where there my local supermarket has 42 line items of something basic like baked beans[1]. More generally it leads designers to use components they are already familiar with, just so they don't have to spend so much time searching and evaluating.

When I started the catalogue for RS components was about 15mm thick, and it was possible to look at every page to see the kinds of things available. Now it would be the best part of 1m, and they don't even print it.

Some strategies that might help...

Look at small web stores to see the kinds of things available. The choice will be limited, but you might even find what you want.

Look at similar projects, which might have clues at to components you do (and don't) want to use.

Learn how to use the search facilities, especially the terminology and filters. Each website is slightly different, but "in stock" and "price ascending" are useful. Some don't have the in stock filter, which means I look at such sites site last (yes RS, I'm looking at you). It takes time to learn the search terms, and you continually have to suck-it-and-see.

For example, Farnell > Rotary switch > in stock > 12 position (near enough 11 ) leads to 29 items including
£4.44 https://uk.farnell.com/lorlin/ck1054/rotary-switch-sp12t-0-15a-250vac/dp/2797208 (not a recommendation!)

Overall... keep learning

[1] Hence I often look at the "reduced section" to (1) reduce the number of choices to make and (2) make me look at things I normally wouldn't even see.

[themadhippy]

Now that is definitely cool. (Decade box using cheap thumbwheel switches.)

as a sidenote ,the version that gives out a binary code are ideal for capacitor substitution boxes

[kripton2035]

Now that is definitely cool. (Decade box using cheap thumbwheel switches.)

as a sidenote ,the version that gives out a binary code are ideal for capacitor substitution boxes

yes see here too : http://kripton2035.free.fr/LabTools/lbt-capacitordec.html

[BeBuLamar]

just for the records, are you aware of this ?
http://kripton2035.free.fr/LabTools/lbt-resistordeca.html

I don't think the OP want a functional decade box. He wanted to make PCB and use SMD resistors much more than how the device actually functions.

[tggzzz]

just for the records, are you aware of this ?
http://kripton2035.free.fr/LabTools/lbt-resistordeca.html

I don't think the OP want a functional decade box. He wanted to make PCB and use SMD resistors much more than how the device actually functions.

He wants to learn.

He is learning, learning many things not directly related to the stated end goal. Good.

He will make mistakes. We all do, even as professionals[1]. That's why there are prototypes, then pilot plants, then production plants. One of the things he will start to learn is the various stages a projectors through, and how.to know when one stage is "good enough" and it is time to move to the next.

In some senses he is doing a "spike investigation", a standard strategy for quickly working out what the most important considerations are before committing to the laborious grind of a full project.


[1] that's assuming the next thing we create isn't a simple variation on the last thing we created. I doubt the OP will fall into the standard trap of confusing 10 years of experience with one year of experience repeated 10 times.

[Analog Kid]

I think it's safely been established that the OP does indeed want to build himself a resistance substitution box, AKA decade box.

Q.E.D.

[BeBuLamar]

I think it's safely been established that the OP does indeed want to build himself a resistance substitution box, AKA decade box.

Q.E.D.

Not! he wanted to do his project which is a rather useless resistor substitution box not a decade box. The project is much more of an excercise in finding parts, designing PCB than learning Watt Law or Ohm Law.

[Analog Kid]

I think it's safely been established that the OP does indeed want to build himself a resistance substitution box, AKA decade box.

Q.E.D.

Not! he wanted to do his project which is a rather useless resistor substitution box not a decade box. The project is much more of an excercise in finding parts, designing PCB than learning Watt Law or Ohm Law.

Well, so what if it is?
Who are we to begrudge their desire to design a PCB and build a project? Just as valid as learning how to compute power or to learn Ohm's Law.

[the offset voltage]

This is the application project from the book.. not my fault.

And to be honest, i like more the incremental increase of the complexity of the projects from the book, if it's not easy for me me to design this simple projects, i can only imagine how it is working on a very complex project with ICs and microcontrollers..

I am curios if other people have started directly with complex projects from let's say a magazine like Elektor, was the learning path much better?

[Analog Kid]

I am curios if other people have started directly with complex projects from let's say a magazine like Elektor, was the learning path much better?

Well, my magazine when I was growing up was Popular Electronics, but same difference.
I did try tackling some projects that were a bit complex and over my head back then. I learned from them, but I found that the simpler projects were much better for learning from. Plus the anxiety level while building them was lower, which helps.

[the offset voltage]

Just curios, if someone copy and paste a projects from a magazine, what does he learn? other than design the pcb, order the components, soldering and testing..

The book that i study is 95% theory and problems, many problems (some with LTspice simulations..), and only one application project at the end of the section, like this famous Resistor substitution box.

[Analog Kid]

Just curios, if someone copy and paste a projects from a magazine, what does he learn? other than design the pcb, order the components, soldering and testing..

Depends. Maybe nothing, as you implied, or maybe a lot, if you have to troubleshoot the circuit to get it to work, or modify it.

If you're curious, you can learn a lot by analyzing a circuit from a magazine or a web site. And by asking questions about it, say on a forum like this.

[the offset voltage]

Hmm, in my case, if i will design a pcb for a complex project, if i will have a problem, i will not have any idea from where to start troubleshooting, as at this moment also the circuits with transistors looks scary to me..

[tggzzz]

I think it's safely been established that the OP does indeed want to build himself a resistance substitution box, AKA decade box.

Q.E.D.

Not! he wanted to do his project which is a rather useless resistor substitution box not a decade box. The project is much more of an excercise in finding parts, designing PCB than learning Watt Law or Ohm Law.

Useless to you? Undoubtedly.

But that's completely and utterly irrelevant. You aren't the "customer", and the customer decides what constitutes "useful", not some random bystander.

[Analog Kid]

Hmm, in my case, if i will design a pcb for a complex project, if i will have a problem, i will not have any idea from where to start troubleshooting, as at this moment also the circuits with transistors looks scary to me..

I totally get that last part! Transistors are scary.

You wouldn't be designing a PCB until you've designed, tested and troubleshooted the circuit. PCB design is about the last step in that process.

To aid in the design of complex projects, you have some tools available:

• Circuit simulators, like LTSpice, which can show you how a circuit works without actually physically building it
• Solderless breadboards which let you physically build circuit and test it

And of course once you reach the breadboarding stage there are pieces of test equipment to help you: voltmeters, ammeters, oscilloscopes.

[the offset voltage]

Can wait to reach transistors i think it will be very challenging

[tggzzz]

Just curios, if someone copy and paste a projects from a magazine, what does he learn? other than design the pcb, order the components, soldering and testing..

The book that i study is 95% theory and problems, many problems (some with LTspice simulations..), and only one application project at the end of the section, like this famous Resistor substitution box.

There is no single thing to learn. There is no single way to learn, everybody uses multiple different mechanisms to learn.

Get inspiration and ideas from a magazine. Understand how and why the circuit is supposed to work.

Learn theory so that you can see limitations and extend the ideas in your own direction, and/or use part of this circuit with part of that circuit to do something new.

BTW, that's also the way to learn to cook: use recipes, understand methods, look in your stock cupboard and work something out.

Unsurprisingly that is well recognised, e.g. in books with titles like "Numerical Recipes in C".

[the offset voltage]

In the book that i have, author wants like some of the problems to be checked only in LTspice. The breadboard and PCB design is only for the end of chapter practical projects.

At this moment i have only a DMM and recently i receive a power supply. I will see for an oscilloscope when i will start AC

[Analog Kid]

Can wait to reach transistors i think it will be very challenging

Good! Keep that curiosity.
Yes, transistors are challenging. They look so simple: a 3-terminal device that amplifies or switches. (They do other things too).
Starting at the simple end, there's the simple formula for beta (the amplification factor):

β = I_C / I_B

But then there's the Ebers-Moll equation:

I_C = I_S [exp (V_BE/V_T) - 1]

which is where my head starts to hurt ...

[tggzzz]

Hmm, in my case, if i will design a pcb for a complex project, if i will have a problem, i will not have any idea from where to start troubleshooting, as at this moment also the circuits with transistors looks scary to me..

Just so.

Incremental design, fabrication and debugging is a skill you need to gain. Understand a bit, design a bit, test a bit, repeat with a different bit, connect those bits together and test.

As for solderless breadboards, some people swear by them; I swear at them. I've seen too many beginners[1] become discouraged because the limitations of solderless breadboards are causing problems which don't happen with other techniques.

Good techniques for early incremental experiments https://entertaininghacks.wordpress.com/2020/07/22/prototyping-circuits-easy-cheap-fast-reliable-techniques/

[1] even experts such as Win Hill (author of the famous "The Art of Electronics") has been caught out by solderless breadboards' has characteristics.

[the offset voltage]

I also want to buy "The Art of Electronics" after i finish with Floyd book

[Analog Kid]

Great book.[1]

Solderless breadboards have always worked for me.
I haven't dealt with any RF (radio frequency) projects, which is where you run into problems with them because of parasitic capacitance. For LF stuff they (usually) work fine.

Of course, everything has its limits and "gotchas". You'll learn them as you go.

[1] A truly fine book. However, don't be fooled when they say you don't really need that much math to use it. In fact, they say in the introduction that they "only" require a "minimum mathematical prerequisite, namely some acquaintance with trigonometric and exponential functions, and preferably a bit of differential calculus".

I find myself stumbling over the math in the text all the time.

[tggzzz]

At this moment i have only a DMM and recently i receive a power supply. I will see for an oscilloscope when i will start AC

I designed and built my first computer (a 6800 with 128 bytes(!) RAM) using only a power supply, switches, resistors plus LEDs, and a 2% analogue multimeter. See the quote in my .sig

The PCBs were just like those in this project https://entertaininghacks.wordpress.com/2015/02/21/a-40-year-old-hack-disinterred/ when I was a couple of years older than you.

I made many mistakes, and learned many things. So will you.