Resistor substitution box project - rotary switch / knob

[the offset voltage]

Hi,

Following  https://www.eevblog.com/forum/beginners/resistor-substitution-box-project-power-calculation/


I want to use this rotary switch from Mouser: https://www.mouser.at/ProductDetail/706-56B36-01-1-09N

But i have no idea how to select the knob for this rotary switch, i don't know how to interpret the datasheet to select the correct knob from Mouser.

Can someone please help me,

Thank you,

[Analog Kid]

Since that switch has a standard 1/4" diameter shaft with a flat, any 1/4" ID knob that has a setscrew will work with it.

See posts below for correction.

[benj38]

The part number you chose has a short slotted shaft meant for turning by a screwdriver. The Mouser image is misleading!
If you want a standard 1/8" shaft you need part number 56A36-01-1-09N. Also note that you chose solder lug connections which are what you need if you want to connect wires to the switch, If, instead, you plan to solder the switch directly to a PCB you will need part number 56P36-01-1-09N (again, this will give you a standard 1/8" shaft).

 @Analog Kid, looking at the data sheet it looks like this series only offers 1/8", not 1/4" shafts.

[Analog Kid]

Oops, my bad. I misread the diagram.

OP, find a switch that has a standard 1/4" shaft, not 1/8". Any 1/4" knob with a setscrew will work, whether the shaft is round or has a flat on it.

[WattsThat]

Nothing to do with the knob… but you should have another look at the switch ratings.

What’s the maximum current you’ll pass through the resistors? 500 ma? 5V 10 ohms from the other post?

What’s the current rating of the switch?

Think that’s a good choice?

[the offset voltage]

Hi,

Yes, thank you for noticing. My mistake 

In this case, i have this option also, but i have the same problem. Can please someone help me, where do i see in the datasheet what knob do i need for this switch, it's not clear to me: https://www.mouser.at/ProductDetail/706-44A30-02-1-09N

Thank you,

[Analog Kid]

I was going to point you to the datasheet for that switch--the link to it is right there on the Mouser page--but for some reason this one doesn't show the shaft diameter. Weird.

But more importantly, why would you choose this very expen$ive, specialized switch?
It's complete overkill for your application.
They have a security feature, similar to the fuel cutoff switches on a Boeing we've heard so much about lately, where you have to push (or pull) the knob in order to change the position. Totally unnecessary for your application.
Did you see the price? $69.84 for quantity one? That's ridiculous.

Just pick an ordinary switch that meets your requirements (# of poles, current capacity). Chances are it'll have a standard 1/4" shaft, so you can use any knob with a 1/4" ID insert with a setscrew. Easy peasy.

[the offset voltage]

Hi,

I am very lost on the selection of this rotary switch. In my case, what will you choose? rotary switch and knob (from Mouser)?

Thank you,

[BeBuLamar]

https://grayhill.com/wp-content/uploads/media/42-44-drawing-01.jpg

I found this drawing for the series 44 and it's 1/4" inch.

[Analog Kid]

This one will work.

Much cheaper ($5.88).
If you look at the datasheet linked there, you see there are two possible shaft sizes: "A" = 6mm, "B" = 6.35mm.
Since this part is a "B" (part # = SR2511F-0109-19R0B-E9-S-W-159), the shaft is exactly 1/4" diameter.
Find any standard knob with a 1/4" insert and a setscrew and it'll work.

Question: why are you even bothering with a resistor decade box? Why not just try individual resistors for your tests?

[Analog Kid]

https://grayhill.com/wp-content/uploads/media/42-44-drawing-01.jpg

I found this drawing for the series 44 and it's 1/4" inch.

But that's for those super-expen$ive, totally unnecessary for the OP's project switches.

[the offset voltage]

Hi, based on the 1/4" inch value, i have a look on Mouser: https://www.mouser.at/c/electromechanical/hardware/knobs-dials/?q=knob%201%2F4%22%20inch
but I still have no idea what to select, will you be king to select the 1/4" inch knob from this Mouser filter link, i am very lost on this 

Thank you,

[Analog Kid]

Hi, based on the 1/4" inch value, i have a look on Mouser: https://www.mouser.at/c/electromechanical/hardware/knobs-dials/?q=knob%201%2F4%22%20inch
but I still have no idea what to select, will you be king to select the 1/4" inch knob from this Mouser filter link, i am very lost on this 

Thank you,

Oh, for chrissakes. That's too much hand-holding for me.
Look: they have a really nice parametric search thingie there. Meaning that you can choose the things you want (knob style, color, size, etc.), click "Apply filters" and it'll only show knobs that fit those criteria.
And the knobs are shown right there below, so you can browse through them.
You start with 626 knobs, which is too many to scroll through.
So set one of the filters--say, black knobs only--to reduce the number. If that doesn't work, try different filters.

[the offset voltage]

Thank you, now i find it

[BeBuLamar]

But any way the switch can only handle 1A which is less than what you need for 5V at 10Ohms. Also the price is high for a device that you are really not going to use. Do you really have to build the unit?

[Analog Kid]

But any way the switch can only handle 1A which is less than what you need for 5V at 10Ohms.

What are you talking about? 5 volts through 10Ω yields 0.5A.

Also the price is high for a device that you are really not going to use. Do you really have to build the unit?

That's my question as well. I seem to remember the original deal was trying to figure out how to control a DC motor, or calculate its voltage/current or some such.
Building a decade box is waaaay overkill for such a project.
Sure, it's a nice thing to have, but it's a bit expensive to build. Maybe wait until you really need one.

[tggzzz]

But any way the switch can only handle 1A which is less than what you need for 5V at 10Ohms. Also the price is high for a device that you are really not going to use. Do you really have to build the unit?

He is learning a lot, fast. That's what he wants and needs at the moment.

[the offset voltage]

Hi,

I am self learning as much as i can from the book Principals of Electric Circuits by Floyd, and this is the application project for Energy and Power section, where i have to design a resistor substitution box.

I like to build it because i also learn PCB design in parallel and i combine the theory from the book with real life PCB design, even if the project it's not 100% real life necessity i learn a lot from it. Thank you

[themadhippy]

Id just buy an elcheapo switch, going by the first you linked to  something likes  https://www.switchelectronics.co.uk/products/ck1029-12-position-1-pole-bbm-rotary-switch-150ma-250v

and move the adjustable stop to suite .And no need for a pcb,just hang the resistors off the back of the switch

[TimFox]

I love Grayhill rotary switches, made near Chicago, but they are expensive.  Here is their complete catalog:  https://grayhill.com/products/rotational-controls/rotary-switches/
That mechanical drawing is not confusing to those who are familiar with mechanical dimensioning, but it is in inches / (mm).
Understanding drawings in that format is an excellent learning exercise for your PCB layout and box construction.
The center drawing shows the shaft diameter clearly (0.125 +/- 0.002 inch = 3,18 +/- 0,06 mm), while the left drawing shows the flat section that keeps the knob from rotating on the shaft.
This switch is designed for nominal 1/8 inch diameter knobs:  in my experience with Grayhill, it is good to use a knob with two set-screws, one of which contacts the flat section, and the other is at 90^o.
Knobs with a single set-screw sometimes get hung up on the transition from round to flat with their shafts.
In my retirement, I use Grayhill switches for projects, but I buy them from eBay, since the new prices are very high, even in US.
Note that they have electrical variations:  for a given set of pins and "throw" angles, they have different part numbers with different numbers of positions.
Some have variable stops that limit the number of positions to less than the maximum.

[Analog Kid]

I am self learning as much as i can from the book Principals of Electric Circuits by Floyd, and this is the application project for Energy and Power section, where i have to design a resistor substitution box.

I like to build it because i also learn PCB design in parallel and i combine the theory from the book with real life PCB design, even if the project it's not 100% real life necessity i learn a lot from it. Thank you

I misunderstood your needs then. A resistor box will be a nice thing for you to have.
One suggestion: if you're going to the trouble to build one, select switches that will handle enough current. My guess™© would be 1A minumum. You should be able to find something not too expansive in that range.
And select resistors that can handle the power: 1/2 watt or 1 watt minimum. You don't want to be letting the magic smoke out of those resistors you so carefully selected and soldered in there.

Also, unless one of your course requirements is also making a PCB, don't bother: just hang the resistors on the backs of the switches, like we did in the olden days.

[tggzzz]

Also, unless one of your course requirements is also making a PCB, don't bother: just hang the resistors on the backs of the switches, like we did in the olden days.

As noted here: https://www.eevblog.com/forum/beginners/resistor-substitution-box-project-power-calculation/msg6011349/#msg6011349

One thing to note is that they are 11 way, for 0 to 10. That's convenient for regular use, but may not be necessary for a learning exercise.

Some N way switches can be installed in such a way that they only rotate through N-1 positions - i.e. a 12-way switch could be set to only have 11 ways. Again, that might not be necessary for this exercise.

[CatalinaWOW]

While decade boxes are rarely necessary, they have their uses.  Easier than fumbling through bins of resistors to find the value you need for a quick breadboard, and cheaper and easier than building the huge compartment trays and sort the resistors into them.

In addition to current capacity it is worth looking at the contact resistance.  It will make a noticeable difference for the resistances that are worrying you about current.

Another less critical, but again possibly important characteristic for your application is "Are the contacts make before break, or break before make configured."  Think about what happens in your application if two resistors are connected at the same time, or if none.

It is questions like these that result in the enormous number of choices that you find for these switches. 

Sorting by price and selecting the in-stock only options will help reduce the number of options you need to look more closely at.

This seemingly simple exercise actually has quite a bit of meat for learning in it.

[BeBuLamar]

But any way the switch can only handle 1A which is less than what you need for 5V at 10Ohms.

What are you talking about? 5 volts through 10Ω yields 0.5A.

Also the price is high for a device that you are really not going to use. Do you really have to build the unit?

That's my question as well. I seem to remember the original deal was trying to figure out how to control a DC motor, or calculate its voltage/current or some such.
Building a decade box is waaaay overkill for such a project.
Sure, it's a nice thing to have, but it's a bit expensive to build. Maybe wait until you really need one.

Yeah bad calculation on my part. Now I think the motor control project and this one are 2 separate projects. He ordered all the part for the motor but I doubt that it will work. I wonder what happened to that project.
He so far works on 2 projects that really don't do much but do take a lot of work and money.

[the offset voltage]

Hi, for the motor speed controller i am now waiting for the PCB from JLC PCB. I will come back with a final update once i receive- soldier components and test the PCB.

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.