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Re: Moving Charge Sensor

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  • Sorynzar
    off to on, and on to off would be great, but as you say it would be complicated. The idea for the circuit is so it can be left unattended and give an audible
    Message 1 of 71 , Dec 2, 2009
      off to on, and on to off would be great, but as you say it would be complicated. The idea for the circuit is so it can be left unattended and give an audible signal when there is a change in the reading, so while good to have both options it is not necessary. So a 555 set up it is. basic poke sent me some good info, can you help me integrate it into the circuit?

      thanks,

      Adam

      --- In Electronics_101@yahoogroups.com, jong kung <jongkung01@...> wrote:
      >
      > Sorynzar,
      >
      >
      > > What I would like to do is have the circuit trigger a buzzer for
      > 1-2
      > > seconds every time the led changes (which for the circuit is every
      >
      > > time a charge approaches or recedes).
      >
      > If you mean a buzzer from off to on state AND buzzer from on to off state, then the logic gets a little complicated (state machines or memory, etc.).  The best and the easiest way is to just use a microcontroller (uC).
      >
      > Few months ago we (here) had a long discussion about something like this.  Some of us recommended using a nand gate (so on to OFF would look like a ON switching), and diodes & caps to keep on signal from canceling out NOT(ed) signal.  But in the end it was kind of agreed, it would be much easier to just use a uC.
      >
      > If you mean just when the LED light (from off to ON state) or vice-versa, then a simple 555 can be used.
      >
      > ====
      >
      > > I also need to be able to switch
      > the audible function on and off. I think a 555 circuit would > be able to
      > achieve this, but I am not sure how to go about doing this.
      >
      > Would a simple ON / OFF switch work for this?
      >
      > If you were to use a uC, this can be done all in software and a momentary switch like a snooze alarm (and it would be trivial).
      >
      >
      > Jong
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    • bobhuish2003
      The drawing at http://www.ece.rochester.edu/~jones/demos/ahern.html showed a 270ohm resistor for the LED. With that value I only get a 4 volt swing from pins 4
      Message 71 of 71 , Dec 13, 2009
        The drawing at http://www.ece.rochester.edu/~jones/demos/ahern.html
        showed a 270ohm resistor for the LED. With that value I only get a 4 volt swing from pins 4 and 10. If I change the resistors to 1k then I get a 8 volt swing. WE have to remember we are using the 4011 as a FET input opamp and will not get a OFF/ON like a gate. You can see it as the LEDs fade in and out.

        Now with the 1ks for the LEDs, and they still light up OK, I have a voltage swing I can work with. I put a 4049 gates on on pin 4 and 10 and now get a clean OFF/ON. I will try a schmitt 74C14 next for the gates. Now with logic outputs you can use the 555 or other ways to sound the buzzer.

        Bob

        --- In Electronics_101@yahoogroups.com, "basicpoke" <basicpoke@...> wrote:
        >
        > Sorynzar,
        > This because pin 10 can only rise to the forward voltage of the LED (a diode). You need a resistor in series with the LED to fix this problem, even if it is a small value, say 10 ohms, you may have to try different values. Also I'm sure you could find an LED that is brighter given the same current.
        >
        > I am finding this thread very difficult to navigate. Maybe you could start a new one, call it "Moving Charge Sensor 2.0" or something.
        >
        > BasicPoke
        >
        >
        > --- In Electronics_101@yahoogroups.com, "Sorynzar" <y2ktachyon@> wrote:
        > >
        > > There is a rise from 0V - 2.10V at pin 10 when the negative charge is present, this is with pins 12 & 13 disconnected. I will rebuild the circuit, maybe even order some brand new bread boards. I will let you know how it turns out.
        > >
        > > Thanks for your help.
        > >
        > > Adam
        >
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