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  1. hevans1944

    Assistance with Transistor Theory

    <sigh>
  2. hevans1944

    Cool circuit plotter with conductive ink

    Folks have been trying for years to lay down conductive traces on an insulating substrate... paper, card board, thin and thick plastic, fiberglass, etc. The only "tried and true" method so far, suitable for both prototypes and manufacturing, is either chemical etching or laser ablation of a...
  3. hevans1944

    Cool circuit plotter with conductive ink

    There are problems with sintering plastic... you need the right kind of plastic. Fortunately progress is being made and a German company has stepped up to address this emerging market. The maker community is not going to give up their plastic string and jump on plastic sintering... the design...
  4. hevans1944

    Cool circuit plotter with conductive ink

    I would like to build a 3D printer that fuses successive layers of plastic powder (instead of melting plastic string) with a high-powered pulsed laser diode. Not real sure how to go about laying down an even thicknesses of powder for each layer though... maybe "dump powder and scrape to a...
  5. hevans1944

    Assistance with Transistor Theory

    Quoting @BobK "Specifically, the Vbe and Ib are related by an equation, so you can think of either as controlling the other." Well, since I did RESET THREAD here, let's talk about relations versus functions...
  6. hevans1944

    Why is relay latching? :(

    It doesn't make any sense to me either. Here is another suggestion: replace the bell and buzzer with an inexpensive 76 dB piezoelectric buzzer, like this one from Radio Shack, rated to operate from 6 V to 18 V DC. Or this 90 dB piezo pulse, rated to operate from 3 V to 28 V DC. There are others...
  7. hevans1944

    Why is relay latching? :(

    Try removing the buzzer and connecting it directly to your five volt supply. Do the same thing with the bell. If both the buzzer and the bell work fine when directly connected to the power supply (no relay contacts, no fifty feet of wire in between) then there may be something wrong with either...
  8. hevans1944

    power supply design help

    Well, the load is constant (100 mA) and the output voltage is constant (5 V), so that looks like a constant-current load on the input filter capacitor and results in a linear discharge rate between power-line peaks. You just have to make sure that linear discharge doesn't go below the minimum...
  9. hevans1944

    simple tone generator

    If you are "testing" woofers, you probably want a nice sinusoidal output with almost zero harmonic distortion and good amplitude stability as a function of frequency. What you need is a Wien bridge oscillator, said bridge having been developed by Max Wien in 1891. If you can find one, the...
  10. hevans1944

    Assistance with Transistor Theory

    Well, it seemed to me we were going way beyond what @Laywah originally requested,,, and there have been no recent posts by the OP, so I hope we haven't overwhelmed or alienated him. Youngsters are more sensitive than old codgers.
  11. hevans1944

    Saturation in transistors (BJTs) - why and how

    Yeah, the transition from linear operation to "saturation" is not abrupt. Brute force is the way to go as long as you don't fry the base-emitter junction.
  12. hevans1944

    Cool circuit plotter with conductive ink

    It brought back some memories from the 20th Century. Glad to see that kids today are willing to re-purpose "obsolete" stuff. It's an excellent way to learn.
  13. hevans1944

    Assistance with Transistor Theory

    RESET THREAD. I can sympathize with that, to some extent. Theory is an integral part of The Scientific Method (TSM), which has been a popular way to try to understand physical reality for several years now. There are other approaches to understanding physical reality, some more successful...
  14. hevans1944

    Saturation in transistors (BJTs) - why and how

    At least one reference defines saturation occurring when the base-emitter junction is forward biased and the base-collector junction also becomes forward biased, as a result of the decrease in collector voltage. I think it does no harm to have a little "too much" base current, just to guarantee...
  15. hevans1944

    2-10v or 4-20 dimming of 120v light bulb

    Do you want to build something from components, or buy off-the-shelf? This company offers a wide variety of solutions, one example at this link. Please provide more specifications: Is this a 115 V AC 100 watt incandescent lamp you are using as a heater? How will you sense the temperature you...
  16. hevans1944

    Cool circuit plotter with conductive ink

    I have a similar plotter in my basement waiting for an application. AFAIK it still works, but the interface is serial RS-232... slow but accurate. I would trade it in an instant for a comparably sized laser printer with the same plotting accuracy and paper size, but I don't see that happening...
  17. hevans1944

    Christmas Gift for my 15 year old electronics enthusiast

    It is natural for a gifted 15 year old to be interested in laser diodes, but these devices are dangerous. I have been working with lasers since the 1970s and shudder to remember the "accidents" that have occurred over the years by people who should have known better, but failed to take even...
  18. hevans1944

    Advice on finding a part?

    Yep. And they won't talk to you because they are playing the CYA game. They want to eliminate the possibility of lawsuits resulting when an unauthorized "repair" goes wrong... for whatever reason. I imagine most users don't torque those potentiometers to destruction. It would help if you can...
  19. hevans1944

    Assistance with Transistor Theory

    The Wikipedia article (almost cited by @KJ6EAD) provides a "beginners" explanation of bipolar junction transistors, or BJTs. The starting equation for BJT design is the Shockley Diode Equation which led to the Ebers-Moll model. As @Merlin3189 implies in his post #9 above, this is only an...
  20. hevans1944

    Assistance with Transistor Theory

    Actually, many of us here love theory. Sure beats trial-and-error, most of the time, if you know what is supposed to happen.
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