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giving a toggle switch memory?...

Discussion in 'General Electronics' started by adder, Apr 5, 2004.

  1. adder

    adder Guest

    I've got a radio with a bass boost toggle switch on it but it always
    resets to "off" when the power is reset. I assume its some kind of
    standard electronic toogle switch arrangement. An LED comes on when
    the switch is "on".

    I thought about simply wiring the switch permanently closed (would be
    like someone holding the switch down all the time) but would this have
    an adverse effect on the rest of the electronics?

    What can I do to make this switch have power independent memory? Can
    I wire up a latching relay in parallel with a kind of feeback so that
    when the switch is pressed it closes the circuit? Then when the radio
    is powered up again the circuit would already be closed. Pressing the
    switch again would (hopefully) open the latching relay.

    Would one of these
    http://www.maplin.co.uk/products/module.asp?CartID=040405132749521&moduleno=20476

    do the job or do I also need to circuit to figure out the toggling??

    Thanks I'm a bit of a novice when it comes to things like this!!

    Steve
     
  2. soundman

    soundman Guest

    the switch you are using is a pushbutton that is only closed when you have
    your finger on it. The whole of its function is controlled by an controller
    inside the radio and therefore, the ideas you mention probably won't work.

    You can try:

    shorting the contacts on the switch so that when the radio turns on if will
    set the bass boost on - this will work as long as the controller doesn't
    look for the switch being open crcuit first.. It may work, it may not.

    Or, if that doesn't work, you will need to make a small circuit that will
    pause after power up, close a relay contact for a second and then open
    again. This will simulate the manual action. If you are able to use PICs,
    one of these will do the job for you with just a few minutes of programming
    and will cost under £ / $ plus the relay

    In both cases, you will find the LED will come on if the bass boost is set -
    as this is also controlled by the microprocessor chip inside the radio and
    is not linked to the button in any direct way.
     
  3. adder

    adder Guest


    Yes this is actually the case. Guess I have to do some learning (or
    just press the button!)
     
  4. Rich Grise

    Rich Grise Guest

    Plus about $100.00 for the development system.
     
  5. soundman

    soundman Guest

    You are quite right if he decides to go to a Microchip development system
    but there are less expensive solutions. The cheap and cheerful hobby
    programmers limit the user to certain types of PIC, but that won't be a
    problem in this case. Any PIC will do the job and as this is such a simple
    application, it is quite possible that a new PIC user can gain the skills to
    do this very quickly. Perhaps as an alternative, someone might be able to
    knock out a PIC for him. That relieves him of the investment and still
    provides a quick solution for him with a minimum of components.

    In fact, as Steve, the original poster, is UK based, I could probably help
    out and send him a PIC if he wants to use it. I happen to have small
    circuit boards that will support a PIC and a relay driver, so Steve, if you
    want one, contact me by email and I'll post one to you.


    The cost of a programmer is often mentioned as a barrier to the use of
    microcontrollers, but most people who ask questions here are willing to
    invest some time and money to get a solution to their problem or to develop
    skills. Whatever technology is selected for a project, there is normally a
    need for a set of hand tools, soldering iron and a meter which can very
    quickly reach the same cost as a programmer. While many people will already
    have at least some of those tools, it isn't unreasonable to consider
    investing in a programmer if they are planning to take on more projects in
    the future.

    Having said that, I also understand that for a one off project, the
    financial investment and the initial learning may prove to be a real
    barrier. There are normally other solutions and I would never suggest that
    microcontrollers are the only way to go or that they provide a better
    solution in every case. Personally, I use them frequently because the
    range of work I do means that I can use them as timers, drivers, logic
    replacements, serial drivers and analogue comparators among other things.
    Using these means that PCB layouts are often identical for different
    applications and new PCBs will normally be variations on existing layouts.
    Despite my preferences, I am concious that even if they suit me, that is no
    indication that they will suit others or their design methods. I am always
    fascinated to see alternative methods and I never fail to be surprised at
    the range of solutions to a simple problem.

    Peter
     
  6. adder

    adder Guest

    Hi Peter, thanks! I'll get in touch by email once I've figured out a
    few things.

    This is a car radio. I was thinking about hooking up a couple of 555
    timers to the power feed so that when the thing is switched on there's
    a momentary delay then a pulse to a relay which would mimick the
    button being pressed. This would give me "on by default" but doesn't
    address the "memory" problem. It'd be nice to have the switch
    remember the last state it was in. I was thinking about using a
    latching relay to enable/disable the pulse on power up. This is what I
    have to think about a bit more. I have a basic understanding of
    electronics but haven't really done any since school days!

    I know this isn't a bit deal but it's quite an interesting problem,
    for me at least.

    Steve
     
  7. Seth Koster

    Seth Koster Guest

    Since the base boost light is a handy reference, why dont you use it
    as an inverted trigger for the 555? That way if the light is off,
    the 555 triggers. If you AND the radio on reference with the NOT
    bass boost light you should get usable logic which waits until the
    radio is on and the bass boost is off before attempting to trigger.
    You might want to clock the logic so you dont have to worry about the
    circuit oscillating from delays in the radio circuit (IE the 555
    triggers, but before the radio processes the request and turns on the
    bass boost light the logic triggers the 555 again, turning off the
    bass boost, etc.).
    If you really want memory, you could use a couple flip flops,
    feeding them with logic from your references/inputs and then run your
    logic from them to the 555, but I'm not sure exactly what you want the
    memory to do. Either way, I'd tend to go with discrete components
    instead of a processor, but thats probably because I'm more familiar
    with them. This doesnt seem like a problem which would need that
    much logic (two bits would tell you everything you need to know,
    regardless of what you need to do with that information).
     
  8. adder

    adder Guest

    Problem is this..
    The bass boost is off by default and is reset by power off/on.
    I want
    * At least boost on by default (at power up)
    * but preferably the last state before power off/on to be memorised
    i.e. if the boost was off before power off it'll be off next time it's
    powered on & if the boost was on it'll be on next time.
     
  9. Seth Koster

    Seth Koster Guest

    Problem is this..
    Bass boost on = A
    Power on = B
    New switch on = C

    My last posting on this subject should handle your first possible
    solution (bass boost at power up). To save the state you could use a
    flip flop which is powered all the time. An easier way, if you dont
    mind adding a switch to your radio, would be to input, into a three
    input AND gate A' B C, and B C' into another AND gate, resulting in
    this logic: A'BC = on, BC' = off. Now the switch should control the
    bass boost directly, with it coming on anytime the radio is on and the
    switch is on and going off if the switch is off and the radio is off.
    The positive aspect of this over the flip flops is that the state is
    saved in the switch and therefore requires no constant power (I
    believe you said this was in a car?).
     
  10. Seth Koster

    Seth Koster Guest

    My previous post should read:

    Bass boost on if power and switch are both on and bass boost off if
    power is on and switch is off.
     
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