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Re: Moving Charge Sensor

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  • Sorynzar
    Yes I think a simple on/off switch would work for the circuit, just put it across the power supply to the 555. The 4011 would be unaffected. I don t currently
    Message 1 of 71 , Dec 2, 2009
      Yes I think a simple on/off switch would work for the circuit, just put it across the power supply to the 555. The 4011 would be unaffected. I don't currently have the ability to work with microcontroller's, I'm afraid I'm stuck in the analogue age.

      Adam

      --- In Electronics_101@yahoogroups.com, "rtstofer" <rstofer@...> wrote:
      >
      >
      >
      > --- 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
      >
      >
      > I might try a couple of capacitors arranged as differentiators to be combined in an OR gate to trigger a one-shot. In fact, a couple of diodes (1N914) could be used instead of an OR gate.
      >
      > Richard
      >
    • 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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