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ROTARY ENCODER interfaced to LED UP / DOWN count display

Discussion in 'General Electronics Discussion' started by John_vk5po, Sep 21, 2014.

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  1. John_vk5po

    John_vk5po

    2
    0
    Sep 21, 2014
    Hi from southern Australia guys!

    Here is my "hopeful application"
    A Chinese made rotary encoder ( open collector A/B o/puts) attached to a rotating shaft (on a roller inductor in an antenna tuning unit) then interfaced via a LS 7183 QUADRATURE CLOCK CONVERTER IC that in turn ( I was hoping!!!) pulses a "Chinese" LED up / down counter module. (0-9999). The LED counter module "saves" the last known number when powered down, so very handy!
    This circuit will not work. RBias was set at 10 Mohms, but the pulses appear to be TOO SHORT to register. Another friend suggested sourcing a leading edge type decoder.

    The counter works a treat when I hit the u/d inputs with a pulse gen.
    The 7183 must not be suitable for what I was told it would do.



    The encoder is a 360 pulses per rev. So many applications I could use it on, aside from the one listed above. for instance, a VERY ACCURATE angle indicator as 1 pulse can be seen on a led counter as 1 degree. (for adjusting the elevation of my 50Mhz antennas to point accurately at the moon for bouncing radio waves back to earth.)

    I have been pulling my hair out for a year or more now, so I would appreciate ANY ADVICE... even another way to achieve what I wish to do.
    Over to some advice please.

    Thanks.
    John
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,491
    2,833
    Jan 21, 2010
    Do you have an oscilloscope to see the output of the LS7183?

    Do you have specs on the rotary encoder, and what are you using as pull-up resistors on its outputs?
     
  3. John_vk5po

    John_vk5po

    2
    0
    Sep 21, 2014
    Hi Steve, I do not have a 'scope now, my lad hijacked it for his projects. A friend has lots of high spec test equipment at his disposal, and has tested the o/puts for me he said. He is a busy fellow, so hopefully he finds the time to help me out a little more.!. BELOW are his observations so far.
    I did not try pull up values on the output of the a/b phases of the decoder. The "specs" claim the encoder has open collector o/puts, that is all I can tell you.

    This is the outcome so far: (snipped from my friends emails)

    The chip ( LS7183) outputs a negative going pulse when turning the encoder. I have set the Rbias to 10M so I have the max pulse width.
    I will try and take a screen cap off the cro tomorrow.
    The shaft decoder works when monitored on an oscilloscope, but the pulses even with the maximum bias resistor are too short to trigger the counter.
    I have tried a few ways to remedy this with the the last being to increase the decoder mode to x4 then dividing the output pulse by 4 to try and lengthen the pulse, this also failed. The clock logic also needed to be inverted, this is another issue but easy to fix.
    The counter that you have requires long positive pulses and may not be that suitable for use with that decoder. Try and get a counter that has an "edge triggered" input rather than a level triggered.


    Thanks Steve,

    John
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,491
    2,833
    Jan 21, 2010
    This is the key aspect. (Assuming that it is true -- and it would have been the way I would have gone if we could confirm the pulses were being generated) then the LS7183 isn't going to work for you.

    As an experiment you could try connecting the two outputs (with pull-ups) to the clock and direction input of your counter and then turning it *slowly*. The counter *may* operate correctly, however it's pretty certain to not do so if you turn the encoder rapidly (also you'll get -- at best -- 1/4 of the maximum resolution of the encoder)
     
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