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Tap Tempo w/ LED Circuit

Discussion in 'Burnt Fingers DIY Effects' started by theorymatt, Jul 15, 2010.

  1. theorymatt

    theorymatt TDPRI Member

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    Attached is a circuit for a tap tempo pedal with LED which lights when the DPDT is depressed. The tap seems to work with my delay. My question is two-fold:

    1) as you can tell from my diagram, I am new at this and am wondering if I am missing something. The resistor I am using with the LED is 470 ohm to keep the LED really bright. Is that too low a value? Do I need a stereo jack for shorting out the DC jack? (the diagram shows a battery, but I will be using a DC jack.) Any other problems you all see with the circuit?

    2) when I plug this into my delay pedal, it seems to work, but I haven't used it for any length of time as I am worried that this circuit might be feeding voltage into my delay pedal (the Fishman Aura Delay - I play a lot of acoustic). Is this the case, and or is this a problem?

    Thank you all for your help!
     

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  2. FenderLover

    FenderLover Friend of Leo's

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    No Good. Remove the "X" wiring on the switch. Use half the switch to turn the LED on. Use the other half to short the tip and ring of your jack. No battery connection to the jack, other than grounding the shield/ring to the (-) battery.
    The 470 resistor should be fine. Depending on your LED, you may want to go to 1K.
     
  3. theorymatt

    theorymatt TDPRI Member

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    Here is the switch I have, which is a DPDT momentary on-on switch:

    http://www.pedalpartsplus.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PPP&Product_Code=9004&Category_Code=SWI

    As you can see from the picture, the lugs run diagonal along the bottom of the switch. Hence, my diagram does not have X-wiring, I was just drawing what I was seeing on the bottom of the switch. I should have drawn it as a traditional switch. That said, I still have a problem, as you stated, I have the batter connected to the jack via the positive lug. I have found a lot of wiring diagrams for reversing polarity with the switch, but none for a 'both-on' at the same time diagram. Is my understanding of the switch as one side Normally-open and one side Normally-closed entirely wrong? Depends on wiring? Lastly, if a switch is designated "Normally Open", does that mean that the switch is open, or the circuit is open-meaning that juice is flowing through the circuit because the switch is connected?

    So attached is a second attempt.... perhaps closer?

    By the way, thank you for your help!

    Oh, lastly, am I totally mistaken that
     
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  5. theorymatt

    theorymatt TDPRI Member

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    Screwed that reply up... attached is diagram two.
     

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  6. theorymatt

    theorymatt TDPRI Member

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  7. frakenstrat

    frakenstrat Tele-Holic

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    gonna build it later and see if it works.
     
  8. theorymatt

    theorymatt TDPRI Member

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    me too. I will post when I find something.
     
  9. theorymatt

    theorymatt TDPRI Member

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    built it. the second circuit works with one change. The tip of jack should be one lug lower than shown on the diagram, so that the tip of the jack is connected on the negative side of the DPDT switch.

    So if you are looking on the diagram the bottom three lugs from left to right would be
    a) tip of jack b) negative battery + jack ground c) LED

    If you are looking on the diagram the top three lugs from left to right would be
    a) nothing b) battery positive c) resistor

    I also changed the 470ohm resistor to a 1.2K resistor just to ensure a decent life for the LED, although it seemed to handle the 470ohms just fine for the limited time I had it that way.

    Thank you fenderlover for putting me on the right track. Let me know if you see anything wrong with this circuit. I can upload a parts list and corrected diagram when I am back at work if anyone is interested, although I get the feeling most of you could have built this in your sleep...
     
  10. theorymatt

    theorymatt TDPRI Member

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    Ok. So everything works, but there is one problem. When the power is not hooked up (I used a DC jack) the tap tempo works as it should. When the power is hooked up to light the LED, the tap tempo works just fine, however, there is an audible 'pop' or 'snap' with each tap made, which is heard through the amp, and which is then heard again at whatever tempo you just set, for however many repeats the delay is set for. This occurs whether the delay is engaged or not.

    Any ideas or solutions?
     
  11. theorymatt

    theorymatt TDPRI Member

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    And another problem.... I have created a short circuit by connecting the battery the way I have. The adaptor powering this small abomination gets extremely hot. So, I guess I will need to rethink this whole thing. Anyone with a better approach?
     
  12. frakenstrat

    frakenstrat Tele-Holic

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    maybe we need a diode or electrolytic to use as a blocker on the DC? i haven't built one yet, been painting my green ringer!
     
  13. theorymatt

    theorymatt TDPRI Member

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    i got it correct now. i will use it tomorrow and see if there are any other problems.

    i will post the corrected circuit on monday, and we'll see if anyone has any suggestions finalizing it.
     
  14. lukerao

    lukerao NEW MEMBER!

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    Would it be possible to see the final diagram?
     
  15. theorymatt

    theorymatt TDPRI Member

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    yeah, sorry to fall off the map, been busy putting new pickups (joe bardens) in my tele. I will dig it up and post it.

    If anyone has any ideas, there is still an audible 'pop' when the tap is first engaged, and a smaller 'pop' on each tap. not loud enough to worry about live, but still annoying. how can i get rid of this power discharge? can i dump the power to ground or something after the LED?
     
  16. radu

    radu TDPRI Member

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    Hi Matt, i am also interested in the final diagram...

    Here's some info for pop elimination from geofex:

    Circuit Cleanups

    There are a couple of minor things that I thought needed cleaned up in the circuit as published. These are not really mistakes, more in the class of polishing. I have changed the original circuit to:

    add an output "pull down" resistor to prevent pops if someone uses this as a switchable stomp box effect

    http://www.geofex.com/Article_Folders/minitub.htm


    and this is the schem:
    http://www.geofex.com/PCB_layouts/Layouts/minitub2.pdf
     
  17. theorymatt

    theorymatt TDPRI Member

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    Attached is the wiring diagram. I am going to make another one and test the 'pull-down' resistor.

    Here are parts:

    1. Switch -No 'click' (I think this is the one I used....)

    2. LED

    3. Jack

    4. DC Jack

    5. LED Resistor

    6. Box. I used this one, but you can put it in here if you really try.
     

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  18. JoshB

    JoshB NEW MEMBER!

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    Thanks man! Going to be integrating this into my true bypass looper!
     
  19. supertele630

    supertele630 NEW MEMBER!

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    Hey folks, I just recently tried to put this together with the most recent diagram and I've run into an issue. The tempo only holds when I hold down the switch. From what I understand, this shouldn't be happening. Can anyone explain what I did wrong, or is this how the DPDT momentary switch works?
     
  20. mac7ry

    mac7ry NEW MEMBER!

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    So, I too am looking to build a tap tempo with LED. Did this one work or are there still issues? Is it silent? Does the tempo stay in after you've quit pressing the pedal? Any and all help is appreciated. Thanks.
     
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