LED on/off using momentary switch help please

Discussion in 'The Projects Forum' started by dickmcjohnson, Jan 1, 2011.

  1. dickmcjohnson

    Thread Starter New Member

    Jan 1, 2011
    3
    0
    Hi folks. I am working on a project that I cannot seem to find a consitent answer for, and I would greatly appreciate any help that anyone can provide. I have a footswitch for a guitar amplifier which changes channels using a SPDT momentary switch. I want to add an LED indicator so that I can tell when the amplifier has changed state. SO, I have ordered a DPDT momentary switch, to allow for the addition of an LED, but I need help with getting the momentary pulse to somehow keep the LED lit until the switch is pressed again. I hope that is clear. I have been looking around, and found many different answers on how to do this, but my knowledge of circuits, and gates is very basic, so I am hoping that someone who knows what they are talking about can take me by the hand and tell me what I need. I have a limited amount of space, so something like a cmos IC that is small would be ideal. Trouble is I don't know how I would need to hook it all up. I will be using a 9v batter for the power source....so basically I want to figure this out using the 9v battery, momentary switch, and LED, plus whatever else is needed to make the light go on with one push of the switch, and off with the next...etc..
    THANKS to anyone who might be able to hlep!
     
  2. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    There is much to know here. Is the spdt switch pushed one way to change channels and the other way to revert to the original channel? Do you want the indicator on the foot switch or on the amp? How is the foot switch wired? Does it have a useful power supply brought in on one of the wires? If you have to use a cable with more wires, why not just bring the power for the LED from the latched circuit in the amplifier?

    Keep talking.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Welcome to AAC!

    You could have an independent circuit, but I would not recommend it. Basically you can make a circuit that will keep track of odd/even when the foot switch is press.

    A little story before I go on. The Three Mile Island disaster had several things go wrong. One of them was an indicator for a critical valve. The indicator would flip states with the valve was open or closes, but it was not directly connected to the valve. So when the valve got stuck once, the indicator was out of sequence. This lead to other bad decisions that escalated.

    You use isn't that critical, but it illustrates what can happen. You are much better off finding where the circuit switches, and put an indicator on that instead, which will give a true reading.

    Which leads us to post #2. We need more information.

    If you want a simple circuit that will keep track of foot switches I can help you. It isn't the route I would go though.

    555 Bistable Multivibrator
     
  4. dickmcjohnson

    Thread Starter New Member

    Jan 1, 2011
    3
    0
    First off, thank you guys so much for your willingness to help. I wasn't sure if I would get a response or not.

    So the SPDT switch which is in there now is NC, and when switch is depressed it opens (at that point, the channel on the amplifier changes), then when it is released the switch returns to its NC state (amplifier doesn't respond). So each time the switch is depressed the channel on the amplifier switches back and forth between its 2 possible channels. I have not received the DPDT switch that I want to replace it with yet, but it should look just like the picture of the DPDT (latching) switch that I have attached here. What I don't know for sure about that switch is whether it will switch back and forth between the throws on the switch when depressed and released, or if it will be a NC, and then break when depressed like the SPST switch that is in there now.

    I am going to try to attach a gut shot of the footswitch here which I hope will serve to clarify how things are laid out. The footswitch originally had a hard-wired cable that was only about 3' long leading to the amp. I was able to replace this using a standard 1/4" jack so that I can use whatever length of cable is most convenient.

    I put my multimeter to the 1/4" cable and got a reading of -18.5 DCV...I hope I am doing that right as I don't use a multimeter very often.

    If this is a useful source of power to light the LED I would LOVE to be able to go that route. I hadn't really considered this as an option, but I like the way you guys think. If it is not useful for lighting the LED I would like to use a standard 9v battery.

    As far as keeping the state of the LED in sync with the state of the channels on the amp, the idea had occurred to me that when the amp is switched off, and then back on it will default to the clean channel (LED off on amplifier), but that the footswitch may still be in the LED on position. This is not anything to worry about really since the fix would be a simple push of a button on the amp to put the 2 back in sync.

    I think it would be great to do as Bill M says and track the state of the amp's switching logic, but I don't want to void the warranty on the amp itself. The footswitch is easily replaced, but I'm not quite ready to begin tinkering with the amp's guts yet.

    I hope this offers some clarification, and thanks again for being willing to help out a noob! You guys rock!
     
  5. dickmcjohnson

    Thread Starter New Member

    Jan 1, 2011
    3
    0
    First off, thank you guys so much for your willingness to help. I wasn't sure if I would get a response or not.

    So the SPDT switch which is in there now is NC, and when switch is depressed it opens (at that point, the channel on the amplifier changes), then when it is released the switch returns to its NC state (amplifier doesn't respond). So each time the switch is depressed the channel on the amplifier switches back and forth between its 2 possible channels. I have not received the DPDT switch that I want to replace it with yet, but it should look just like the picture of the DPDT (latching) switch that I have attached here. What I don't know for sure about that switch is whether it will switch back and forth between the throws on the switch when depressed and released, or if it will be a NC, and then break when depressed like the SPST switch that is in there now.

    I am going to try to attach a gut shot of the footswitch here which I hope will serve to clarify how things are laid out. The footswitch originally had a hard-wired cable that was only about 3' long leading to the amp. I was able to replace this using a standard 1/4" jack so that I can use whatever length of cable is most convenient.

    I put my multimeter to the 1/4" cable and got a reading of -18.5 DCV...I hope I am doing that right as I don't use a multimeter very often.

    If this is a useful source of power to light the LED I would LOVE to be able to go that route. I hadn't really considered this as an option, but I like the way you guys think. If it is not useful for lighting the LED I would like to use a standard 9v battery.

    As far as keeping the state of the LED in sync with the state of the channels on the amp, the idea had occurred to me that when the amp is switched off, and then back on it will default to the clean channel (LED off on amplifier), but that the footswitch may still be in the LED on position. This is not anything to worry about really since the fix would be a simple push of a button on the amp to put the 2 back in sync.

    I think it would be great to do as Bill M says and track the state of the amp's switching logic, but I don't want to void the warranty on the amp itself. The footswitch is easily replaced, but I'm not quite ready to begin tinkering with the amp's guts yet.

    I hope this offers some clarification, and thanks again for being willing to help out a noob! You guys rock!
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    18VDC? Try a 3300Ω (3.3KΩ) ¼W resistor with the LED, see what it does. It will draw approximately 5ma, so it shouldn't be too heavy a load. 18V is a bit high for most logic, but you might be able to get by with it.

    Look for a voltage that switches. If such exist it would help the cause.
     
  7. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    Minor spooky: If the LED uses too much current, it will trigger the amp to change channels. If that happens, you are stuck with using a battery.

    I have not used momentary stomp box switches. If yours is truly momentary, and you have to use a battery, you will need a latching circuit to keeep the LED on.
     
  8. GroundZero

    New Member

    Jul 30, 2011
    4
    0
    Hello Dick.

    I have a circuit board just for your application.
    If you are still interested reply to this post and
    we can exchange contact info from there.

    GroundZero
     
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