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OT - Rotary Position Sensor / "Address Switch"

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  • OT - Rotary Position Sensor / "Address Switch"

    I need to make a control panel with some rotary switches to select a number. For instance, the first rotary switch would be 0-9 for the 10s place and the second rotary switch would be 0-9 for the 1s place to allow a selection of 00 through 99.

    The tricky part is that I'd like a digital output, preferably 8 bit. Now I've got some ideas how I can do this piece-meal, but I got to wondering if there wasn't a pre-made unit that does this. I was thinking about similar devices I know there are both analog and digital rotary encoders; something that my CNC machinist friends are very familiar with.

    So ... my question is: do they make a " 8-bit rotary encoder" that has well defined positions, instead of a continuously variable shaft? As a special bonus, I'd like this to be reasonably priced. I don't need to measure any precise rotation measurement, just an 8 bit output from 00000000 to 01100011. Other possibly acceptable alternatives would be something that reads out data on "two wire" communication like an I2C bus.

    Thanks!

  • #2
    Thumbwheel switches - available in binary, binary-coded-decimal and others. Usually only 4 bits out per digit. I have seen 10-position rotaries with BCD output, but they are not common.
    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
    ~Practitioner of the Electromechanical Arts~

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    • #3
      I used to get my rotary switches from Grayhill, they will supply coded wafer type, or simply get one with a 2 or 3 wafer stack, or however many you need to give you a binary or BCD.
      Most of the commercial CNC's use this Binary coded method for Feedrate etc.
      DigiKey sell Grayhill. Also a bunch on ebay.
      For 100 position indented switch, you can use the standard PWG or handwheel, this has 100p/rev output.
      Max.
      Last edited by MaxHeadRoom; 04-03-2013, 02:08 PM.

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      • #4
        Yes, they make a 8 bit absolute rotary encoder. The only thing it is 256 positions.

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        • #5
          As Weston said, rotary BCD switches are available. They tend to be rather expensive though. This would be an example of a nicer panel mounted one, this one is somewhat cheaper but it's PC board mount

          How are your soldering skills? You can combine a nice panel mount rotary switch (you'd have to add the numeric legends of course) like this one and a 10 to 1 priority encoder chip such as the HC147 for each channel to provide a BCD encoded output.

          The easiest way I can think of to get 8-bit binary (as opposed to BCD) for two switches is to use a small microcontroller to read the switches and output binary. Simple if you already have the tools, a steep learning curve if you don't.

          -Lyndon
          Last edited by lwalker; 04-03-2013, 02:27 PM. Reason: Fixed link

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          • #6
            Thanks, guys. Think I've found some promising leads. Much cheaper and simpler to buy one then have to cobble anything together.



            Lyndon - BCD or 8 bit absolute is fine. The output is read by a microcontroller through a shift register, so I figured the easiest thing was absolute binary. It doesn't really matter what the coding is, as long as I've got a data sheet to explain it Seems like two of these would get the job done and, at ~$6 a pop, they won't break the bank: http://www.mouser.com/ProductDetail/...ihNtuEUnflc%3d
            Last edited by Fasttrack; 04-03-2013, 02:37 PM.

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            • #7
              The problem with your original request is you wanted a 0-99 binary output from two BCD (Binary Coded Decimal) switches. I have seen a lot of switches, but nothing that would allow you to do that. If it exists, it would probably be expensive.

              But your latest response seems to indicate that strict binary coding is not a necessity. If that is true, then any ten position coding switch with four output lines would work. The units digit switch would give you the four right most or least significant binary digits. Then the tens switch would give you an additional four higher order, binary digits. You get eight digits that consist of two four bit groups. The processor that you apparently intend to use can easily translate these to whatever format you want from there. Almost any of these thumbwheel types would do:

              http://www.digikey.com/scripts/dksea...tity=0&PV447=1

              Or there are rotary types.

              http://www.digikey.com/scripts/dksea...88=10&PV837=12
              Paul A.

              Make it fit.
              You can't win and there is a penalty for trying!

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              • #8
                Not sure about buying a product that would fit the specific task, but chucking one together isnt difficult and can done using simple TTL or CMOS logic (Decimal to BCD encoders). This way you could get two standard 10 position rotary switches and have a true BCD or BIN output generated from them. Would require a perfboard or PCB, but the chip cost is low (< $1.00 each). Display is easy with 7 seg decoder/drivers, with some being multi digit units in a single chip.

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                • #9
                  If the output is read by a microcontroller.. Why do you care?
                  Just reprogram the microcontroller to read two seperate switchs and combine the result.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    How often will they be used, the ones the OP pasted only have a 625 rotary life.

                    Peter
                    I have tools I don't know how to use!!

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                    • #11
                      This is an important point. Some of the PC board mounted switches are intended for an initial set up and OCCASIONAL changes only, not continuous use. Do look at switches that were intended for front panel mounting. They should have longer operational life. And do look at the data sheet for that life estimate.

                      Originally posted by ptjw7uk View Post
                      How often will they be used, the ones the OP pasted only have a 625 rotary life.

                      Peter
                      Paul A.

                      Make it fit.
                      You can't win and there is a penalty for trying!

                      Comment


                      • #12
                        OT Reply

                        Originally posted by ptjw7uk View Post
                        I have tools I don't know how to use!!
                        And I have uses I do not know how to tool.
                        Paul A.

                        Make it fit.
                        You can't win and there is a penalty for trying!

                        Comment


                        • #13
                          As already mentioned, A three BCD thumb wheel switch bank multiplexed will give you:
                          1/Operator Panel mount
                          2/ 0-999 selection and readout
                          3/ Four input - three output = one 8bit Micro port for all three TWS.
                          You can buy them with multiplexing diodes or fit e.g. 1N914's externally if needed.
                          Also a 4x4 keypad would give you data entry and use an 8 bit port.
                          Max.
                          Last edited by MaxHeadRoom; 04-05-2013, 11:49 AM.

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