Replace Push On/Off Switch

Discussion in 'General Electronics Chat' started by abdulk79, Jan 8, 2016.

  1. abdulk79

    Thread Starter New Member

    Jan 8, 2016
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    1
    Hi,

    I have a car amp which is turned on using push On/Off Switch (gives gnd signal to IC), so every time I start the car I have to turn on this amp separately. My car stereo gives out 12v +ve on a wire when turned on.

    Can I use this 12v to build a circuit which will trigger my amp and eliminate push On/Off Switch?

    Thanks
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Sure..
    NEVER seen an automotive amp that didn't feature a turn on wire though...

    I assume by push on/off you a mean momentary switch.
    A 555 monostable circuit could do it..
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
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    You may want to put a delay on it to avoid the additional load when you're trying to start the engine. Unless your stereo is already on a start cutout circuit.
     
  4. abdulk79

    Thread Starter New Member

    Jan 8, 2016
    10
    1
    Yes momentary switch. (press once and leave).

    Please help me with circuit diagram.. circuits I have seen still have switch which gives -ve signal on pin 2 to trigger. I have a continuous +12v once stereo is ON.

    What is the output of the circuit? i need -ve
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Have you tried holding the switch closed when power is applied to see if the system powers up automatically? Could save a lot of effort. If that doesn't work...

    1. Are you sure the current switch gives a GND signal to the amp when pressed?

    2. What is the open circuit voltage on the switch terminals?

    3. What is your skill set and what components do you have or have access to?

    This can be done with two transistors, or two sections of a CMOS gate chip plus one transistor, or two 555's, or only 1 555 if you're tricky, etc. Or, a PicAxe, an Arduino...

    ak
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    If there is no need for a short delay between when power comes on and when the switch input is activated, then this can be done with 1 capacitor (and an optional diode for a faster reset). No active devices, and no LM741 opamps. Connect a capacitor from the switch input to GND. That's it. The cap will hold the switch low enough to start the amp, and the internal pull up impedance will charge up the cap to release the input after a short time. Since we don't know what the pullup current is, the cap size is determined by trial. Start with something like 10 uF to 100 uF, negative end to GND, positive end to the switch input.

    The amp input might not discharge the cap very quickly when power is removed. You can speed this up by adding a small signal diode (1N914, 1N4148, etc.). Anode to the switch input, cathode to +12V power.

    ak
     
    Last edited: Jan 8, 2016
  8. abdulk79

    Thread Starter New Member

    Jan 8, 2016
    10
    1
    Circuit.png
    This is what my circuit looks like.. single press activates the AMP, if i keep the button pressed it goes into safe mode.
    I want to trigger that single press with a circuit which in turn will be driven by +12v from my stereo. +12v will always be on so I want a circuit which just triggers for 1 sec and then goes in to sleep mode until +12v is removed and reapplied.
     
  9. abdulk79

    Thread Starter New Member

    Jan 8, 2016
    10
    1
    Dodgydave likes this.
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