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  1. BobK

    Small Device for Sound

    MP3 player? Bob
  2. BobK

    Different ways to discharge circuits?

    A capacitor discharging thorugh a resistor goes to 1/e of it's original voltage in RC seconds. The 5 gives a discharge to 1/e^5 or 0.0067 times its original voltage. Throretically, the voltage never reaches zero, so the time to completely discharge a capcitor is infinite. Bob
  3. BobK

    A bunch of dead LEDs from Radio Shack?

    If you are using a 10K resistor, some of the "dead" LEDs might just not be bright enough to see at the low current you are testing them with. Try them again with a 1K and then a 100R if you haven't emptied the trash yet. A blue or white LED can take as much as 3.6V at it's rated current. Bob
  4. BobK

    Capacitors

    When a DC voltage is placed across an uncharged capacitor a current flows into the capacitor until the charge across the plates creates a voltage that matches the applied voltage, then no more current flows. So in the steady state, a capacitor "blocks" DC. When an AC voltage is applied to a...
  5. BobK

    A bunch of dead LEDs from Radio Shack?

    I would be very surprised if a pack of assorted LEDs are all bad. What are you using for power? Is it possible IT is bad? Bob
  6. BobK

    My Power Supply Black Outs

    I don't see how the PIC and a solid state relay could be taking .5 A. Something is wrong. Bob
  7. BobK

    Idiotic statements from Engineers!

    I resemble that remark! Bob
  8. BobK

    My Power Supply Black Outs

    Agreed, I thought you were measuring the 1V drop at the input to the regulator. Bob
  9. BobK

    Choosing a power supply

    Either one would do. I would not choose based on switching / linear, but I expect the linear ones will be considerably less expensive. You probably will want one that can do either constant voltage or constant current, and has meters for each. I find a couple of these for about $80 on...
  10. BobK

    My Power Supply Black Outs

    A 1V drop would not be unexpected and would not affect the output of the regulator. Is the relay really a solid-state relay as shown in your original schematic or is it an electromechanical relay? If the latter, you should have a reverse biased diode across the coil to supress the voltage...
  11. BobK

    What Is This?

    They are, with absolute certainty, some kind of surface mount electronic parts. Why does it matter whether they are LEDs or not? Would you be worried if they were reistors or capacitors? (They are not "chips" (ICs) since those would require more than 2 leads.) If you insist on testing them...
  12. BobK

    What Is This?

    Look! I got some in the mail too! Global conspiracy! Let me check where they came from. Oh, Mouser.com, never mind.
  13. BobK

    LED vs Incandescent

    If you had two incandescent bulbs in parallel, then replaces one of them with a resistor and LED, and the other incandescent bulb stopped lighting, I would say you wired something wrong. Bob
  14. BobK

    Driving a powered speaker using a microcontroller

    PWM output from a micontroller should go through a simple RC low-pass filter, then it is suitable to put into a line-level audio input. Bob
  15. BobK

    D/A converter

    What is the problem with building this exactly as shown? Bob
  16. BobK

    Sinewave (~1.5 Mhz range) switching.

    How you wouild do this depends on the voltage and current you want to switch and the frequency at which you want to switch it. Bob
  17. BobK

    LED flash lite: Max Current vs forward voltage (dropping)

    Okay, I misunderstood. Yep, acts just like a resistor, wasting power. The efficiency comes down to simply Vout / Vin. Yep, the inductor dissapates no power except for that of the series resistance. Use a really large (dimensions, not inductance) inductor and this can be reducted to near...
  18. BobK

    The best way to test cap voltage with adc?

    What is wrong with putting huge resistors in the divider? Microchip ADCs typically need an output impedance of 2500R or less, so you can use anything up to that in the lower resistor, giving you 25 times less current drawn. Or you can use and opamp and even larger resistors. Bob
  19. BobK

    Transformer question

    A transformer does act as a low-pass filter since there is a lot of inductance. So, when fed a square wave it is naturally going to smooth it out somewhat. Bob.
  20. BobK

    Inverter ... Mr. Gary Lecomte

    If you are really interested, here is a paper about the technique I described: http://ww1.microchip.com/downloads/en/AppNotes/01279B.pdf Bob
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