Bill Marsden's Test probe?

Discussion in 'The Projects Forum' started by bundick, Oct 16, 2009.

  1. bundick

    Thread Starter Active Member

    Dec 19, 2007
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    Bill put up this test probe on another thread. If the frequency we are looking at is so high it makes the LED glow as if your looking at a steady state, is there a little discrimination circuit we could adapt so the Cmos input would see only every 4th or 100th pulse?
    Cmos test probe.gif
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Yes, a divider. But why not add a speaker instead, you can hear to 20khz more or less.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Here's a logic probe that shows the logic state:

    [​IMG]

    If the green LED is lit, the input is high; if the red LED is lit, the input is low or disconnected. If they are both lit, the input is constantly changing states.

    If you wanted to improve on it, you could use a 40106 which is a hex Schmitt-trigger inverting buffer. You could also use a 4093 quad Schmitt-trigger NAND, and just tie each two inputs together to change them into inverters.

    As shown, R2 is selected for operation at 5v. If you wish to use it at up to 15v, you will need to increase the value of R2.
     
    Last edited: Oct 16, 2009
  4. Wendy

    Moderator

    Mar 24, 2008
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    I liked this idea, it could be easily modified to CMOS by changing the chips out on the front end.

    Project: TTL Logic probe.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Yep; a CD4047 and a 4093 or 40106 would do it.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    My probe can be converted to Cmos.
    Keep in mind that Cmos has a lower current output for the leds.
    Perhaps add some buffers for the leds.

    Greetings,
    Bertus
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    I was figuring on CMOS on the front end, the existing schematic on the back. Basically matching logic to logic.
     
  8. bundick

    Thread Starter Active Member

    Dec 19, 2007
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    I aplogize for not getting back. I didn't get any notifications of reply's.
    Too late in the day to think now.
    Dick
     
  9. bundick

    Thread Starter Active Member

    Dec 19, 2007
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    OK, looking at both the probes, it seems like that's a Digital sensing device.
    What if I'm looking at a wide range of AC, such as a Sound amp?
    Or the output of a Coil or transformer coil that is sensing a Rotating magnet?
    Will those spikes kill the Cmos Logic probe?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    They are.
    Most likely, yes.
    Neither TTL nor CMOS IC's should be subjected to voltages outside of their "rails", or they may be destroyed.

    TTL uses power rails of ground and Vcc (+5v); the +5v can range from 4.5v to 5.5v
    CMOS uses power rails of Vss (ground) and Vdd; Vdd's normal range is between 3v and 16v. Some 4000-series CMOS IC's will go up to 18v.
     
  11. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
    1
    thanks,
    So for my monkeying around with small generators I should use Bills probe with a current limiter in the input of a 222 Transistor, a 12V supply with a current limiter, and a parallel circuit to protect the LED.....
    The next step is to make a probe with two LED's. A positive LED and a second LED to show a negative going pulse. Below Zero Volts.

    I am thinking of making a trickle charger on a small engine. I have a large chunk of Ferrite with three legs, and some wire wrapped around its legs.

    I think the Flywheel has a large magnet oriented +- going by, then followed by a smaller magnet oriented -+.
    I think I'm going to get three large rises followed by three smaller negative going spikes.

    A volt meter is too slow for this stuff. (I have both kinds)

    When I saw Bill's schematic I thought this might be just the thing. Thanks for your inputs. I see its going to be some thing else now.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Gee, why not just get an alternator out of a junked compact car, hook it up to the gas engine with a V-belt and wire that in?
     
  13. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
    1
    Sarge I went over that last two months. It's just not feasible.
    Back in the 50's I worked on some motor cycles (Brit's) that had a small Generator up front for Six volts. It had to run faster than the engine.
    To do the same with a Lawn mower engine or small outboard the engine turning 3600, the Alt would be turning 7000 to get what the out put needs to be in order to operate a starter. Only a Briggs 5 hp and above has the torque and sturdy oiling system to do that.

    My idea is to make a trickle charger that would charge a Capacitor to operate a pair of small solenoids. The whacko inventor at work here :)
     
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