using thumbwheel switches with plc's

I would like to know how thumbwheel switches work in plc's.How the ladder logic is written?

Is this the last assignment of the Autumn term,

Or the first of the Spring term?

What is and isn't allowed in this assignment?

as starter
not a and not b and not c and not d equals pos 0
a and not b and not c and not d equals pos 1
not a and b and not c and not d equals pos 2
etc
however you will need some diodes if you have more then one wheel
better to have every output of the wheel to an input of the plc

you may take this code however you must insert the source if in school even better your grade will rise when you use code from several sources it means you are thinking instead of just typing code.

Most thumbwheels I have ever worked with were BCD coded, so all you need to do is read the DIns Byte-wise or Word-wise and use the BCD commands (if available on your PLC) directly, couldn't be easier.

The BCD thumbwheel apps I've seen use a "Write" momentary button. When the button is depressed, in AB plcs, using a one shot, you can move the input word to a holding register and convert it in one step.

Greetings rickakins,

if you're looking for basic "thumbwheel" information maybe this post will help ...

if you really want detailed information on how the "ladder logic is written" then you need to tell us what type of PLC hardware you're using ... different brands have different methods of doing the same job ...

and welcome to the forum ...

Usually they are BCD coded, therefore:

Assume we have a thumbwheel 0-9.

4 inputs from it - 1,2,4,8 (BCD) and we connect these inputs to Input word 3 and it represents 1 group of 4 in the word like...

input word 3 = 0000 1111 0000 0000 so the second set of 4 from the left is where we have our inputs connected. These are I 3.8, I 3.9, I 3.10 and I 3.11.

LOAD Input word 3 //scan our inputs
LOAD 0f00 //need to mask the word to ignore other inputs in word 3
AND WORD //masking bits
SHIFT RIGHT WORD 8 places //to place the inputs in the 4 LSBs
TRANSFER some other place //where the result is exactly the number you see on the thumbwheel.

The result can be used then to call product specific data from different areas etc.


cheers

I used to have about a 100 machines with 4 gang BCD thumbwheel switches. I haven't seen them in over 8 years, and I don't miss them.

How did they work? Quite Well, suprisingly.

All new machine upgrades were getting Maple Displays with a touch pad for setting parameters.

Don't think I would go back to thumbwheels.

So, as an answer to the student question, they work quite well, until you decide they are probably impractical in modern equipment and get a decent (but probably very pricy) interface.

By the time you buy an extra 16 inputs, design, progam, wire, and test, it is cheaper to spend a couple hundred $$$ for a low end interface/display.

Sad thing is, what few plc books I've seen on inter-library load, at Borders, and at Barnes and Noble, (even with recent copyright dates) are all outdated and still tout bcd thumbwheels.

Oh well.....casey

Wait a min.

Easy touch touch screens( automation Direct) has thumb wheels on the screen, does this count.

NO!