Open/Close switch LED Bargraph LM3914

Discussion in 'The Projects Forum' started by dwight_talley, Oct 13, 2010.

  1. dwight_talley

    Thread Starter New Member

    Oct 13, 2010
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    I am looking for a simple bargraph circuit that will indicate how long a button is pressed. Full bargraph when button is held for 2 seconds. (adjustable down to 1 second) The leds will ramp up and down during the time the switch is closed and open.

    The circuit should run from 12volts.

    As simple as possible. I assume a 555 timer with a LM3914 ic will be needed.

    The switch will be a standard TLP621 optoisolator connected to a computer.

    This circuit will be used to indicate when corrections are sent to my telescope mount when it is tracking stars.

    Thanks for any info you can provide.


    Dwight
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hey welcome

    This will be a good project.
    Give us more info from ur side.

    This can be done quite nicely
     
  3. dwight_talley

    Thread Starter New Member

    Oct 13, 2010
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    When guiding a telescope, the computer makes small corrections which it sends to the mount. I want a visual indicator that shows the amount (time) of corrections and any trends. With 4 of the bargraphs setup to indicate the four directions, I will be able to see what the computer is telling the telescope. The optoisolator will prevent ground loops and interface issues.

    Simple circuit is best since you cant just drop into Rshack anymore and get parts.
    The powersupply should be 12 volts but I guess a voltage regulator to reduce it would work.

    Thanks

    Dwight
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Some sort of position Indicator. Like tracking, right?
     
  5. dwight_talley

    Thread Starter New Member

    Oct 13, 2010
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    No, just a switch activation indicator with the amount of time the switch is open indicated by the amount of led lights turned on. If setup to where a 1 second switch activation gives all leds lit. A half second activation gives 5 bars lit and so forth. It would give a visual trend on what direction is being activated the most and for how long.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    OK.. So input is from LPT to an Opto?
     
  7. dwight_talley

    Thread Starter New Member

    Oct 13, 2010
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    I can use a pc lpt port or the two autoguider devices I have that have the signal current to run the optocouplier.

    I have learned that I can just have a voltage on the LM3914 to activate all of the bar graph. LM3914 chip as is goes from none to all 10 LED's lit when an input at pin 5 (18 pin DIL packake) goes from 0 to 1.2 V.

    That may be the best option. Just put the voltage on the optocouplier and if the switch is on, it will lite all of the leds.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Don't sell yourself short, I like the orifginal idea even if it would take a few extra components to do it right.

    Can't use a simple RC curve due to the non-linearity but a 555 set to operate at 10 (or 5) Hz into a 74491 10-bit Binary Up/Down Counter (or an 8 bit + part of another) with a resistor divider network would put out "steps" of voltage to the 3914.
     
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