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  1. BobK

    spring/plate reverb

    That is not how an LM386 is used. Did you look at the application circuits? You simply ground the - input and put the signal to the +. That will give you a gain of 20. A 10uF across pins 1 and 8 will up the gain to 200, which is probably more like what you want. Building an audio amp out...
  2. BobK

    2 LED's circuit (not so simple as it sounds)

    Yep, I see that now. KrisBlueNZ solution does look right though. Bob
  3. BobK

    2 LED's circuit (not so simple as it sounds)

    No, when the probe (which is called In in my circuit) is high impedance, neither LED lights since both LEDs are connected ot the probe on one side. Edited: Never mind, you are correct!. Bob
  4. BobK

    2 LED's circuit (not so simple as it sounds)

    That is the same as my circuit except the resistors are on the other side of the LEDs. Bob
  5. BobK

    spring/plate reverb

    An audio amplifier is more complicated than that. Use an LM386 chip. Bob
  6. BobK

    2 LED's circuit (not so simple as it sounds)

    If you have a ground available, there is no problem at all! The solution is totally obvious:
  7. BobK

    2 LED's circuit (not so simple as it sounds)

    Here is the solution, assuming a red LED with 2.0V and 20ma and a green LED at 2.5V and 20ma. +!4 is the node that is at 14V and In is the node that is at one of 3 states.
  8. BobK

    2 LED's circuit (not so simple as it sounds)

    Green Giant's solution requires a ground. If you have a ground, it is much easier that that. You simply connect the red LED between the node 1 and node 2 and the green one between node 2 and ground. But I am guessing that you have no ground available, only the two nodes, is that correct? Bob
  9. BobK

    Help needed for simple problem

    He said that it rises like a ramp from 1V to 3V over time and then returns to 1V. I am only questioning what the return from 3V to 1V looks like. Is it a triangle or a sawtooth. Bob
  10. BobK

    Help needed for simple problem

    Basically, you would want to duplicate the function of a 555 timer, with some enhancements. You could use a constant current source to charge a capacitor and a schmitt trigger with a 3V threshold and 2V hysteresis. You didn't say how the discharge should go, it you want it to be (nearly)...
  11. BobK

    Capacitor help

    Laplace's calculation is actually a bit exaggerated. You can allow the capacitor voltage to sink as it is discharged by using a boost converter to bring it back up to the level needed to light an LED. The best way to look at is in terms of energy and efficiency. First, you need to know how...
  12. BobK

    Help: need to find PCB design + assembly companies

    Isn't there someone at your school who can help you design and make your own? Bob
  13. BobK

    Chat_Ghosty's PSU

    Correct, except the rectified 120V will be more like 170V. The peak voltage of a sine wave is sqrt(2) times the RMS voltage, and a bridge rectifier with smoothing capacitors will produce something close to the peak voltage when not loaded. Bob
  14. BobK

    Correct way of converting 12v down to 3.3 for a pin input?

    Great explanation Steve! I have now learned something: be careful using a zener to clamp a voltage when the current through it will be low. Bob
  15. BobK

    How to connect POT and how this regiulator based charger behaves?

    The circuit is a constant voltage source with current limit. This means it will maintain the 4.2V output as long as the current stays below the 600ma current limit. If the current were to exceed 600ma, the voltage is reduced to keep the current from going any higher. As the voltage on the...
  16. BobK

    Chat_Ghosty's PSU

    The metal frame is being used as a heat sink. Bob
  17. BobK

    LED Buck Driver

    When you parallel the LEDs they are sharing the 350ma current (possibly not equally). When they are in series each is seeing 350ma, so yes, they should be quite a bit brighter. This is the preferred way to wire multiple LEDs to a constant current source. Of course the input voltage must be...
  18. BobK

    Need to make a circuit to power flourescent lamps?

    A Tesla coil, build a Tesla coil and any floursescent lamp nearby will light up! Bob
  19. BobK

    Correct way of converting 12v down to 3.3 for a pin input?

    Sounds like it is actaully a 1.8V zener diode then. Bob
  20. BobK

    Correct way of converting 12v down to 3.3 for a pin input?

    Check the polarity on the diode. Most likely you have it reversed. The Anode should be at ground. Bob
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