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  1. BobK

    Simple transistor circuit problem

    I don't think he is using that circuit anyway. Bob
  2. BobK

    Audio Signal ADC

    Did you connect the output of the op-amp to the - input? This is how you make a voltage follower. Bob
  3. BobK

    Band-Pass Filter Help

    It is pretty much impossible to do an active filter design by hand. Did you try the design software I linked to? It will give you a working design based on the parameters you input for center freq and bandwith. Bob
  4. BobK

    Simple transistor circuit problem

    Another reason in favor of using microcontrollers is this: You could connect them all together to a master and insert your own patterns onto the display, which might make for some interesting, perhaps even dazzling effects. Kris's answer for controlling the discharge rate is a good one...
  5. BobK

    Audio Signal ADC

    Your envelope detector has a 1M resistor to provide an RC time constant to drain the capacitor. Connecting this to a voltage divider drastically changes this resistance. You need to put a high impedance buffer (op amp voltage follower) between the envelope detector and the ADC. Bob
  6. BobK

    Simple transistor circuit problem

    I would use a 64-pin micro to control 7x7 LEDs with an individual driver for each one, no multiplexing. Cost of the micro is < 1 pound, and you would need 7 ULN2003 driver chips (nice how that works out 7 drivers per chip). And you are at 3-4p per LED for those components. I would use a...
  7. BobK

    PIC Programmer using USB Keyboard

    Interesting idea. Basically, using the LEDs on your keyboard as a SPI port. Bob
  8. BobK

    camera is crystal radio when placed on top of oscillator in broken tube radio?

    I was thinking the same thing as I read your post. Bob
  9. BobK

    Current Surge

    As I said before, the inductor is way to small as well. At 48V stepping down to 12V, there will be 36V across the inductor. The formula for current in an inductor is: dI/dt = V / L For a 1 uH inductor with 36V across it dI/dt = 36,000,000 A / sec Or 360A / PWM period. You want to...
  10. BobK

    Current Surge

    The capacitor is way too high for 100KHz. I assume the plot is the voltage acorss R1. If that is correct we are talking about 2A. A 2200uF cap would only lose 0.009 V in the PWM period. There is no reason to control the ripple to that level. I stick to my reccomenation of 1 to 10uF. And...
  11. BobK

    Simple transistor circuit problem

    80000? I hope your budget it large. In answer to your question. Yes, but with help. It would not be practical to control them all with 1. I would make a standard panel with maybe 4 x 4 and have each panel have it's own microcontroller. My question is how many components do you think it...
  12. BobK

    Current Surge

    1uH is way too low unless the PWM freq is int the 10s of MegaHertz. And the 2200uF cap is way too high, try about 10uF. What is the PWM freq? Try something like 100uH to 1mH. Since the duty cycle is 100%, you are simply turning the MOSFET on. The surge is the battery trying to charge...
  13. BobK

    Controlling Twelve Steppers

    Steve, I can do even worse: 12 steppers can only be controlled by a higher power. Bob
  14. BobK

    Current Surge

    Show us the circuit. Bob
  15. BobK

    Audio Signal ADC

    Running the audio signal through an envelope detector will not sample the audio signal, only it's peak value over a time period. Is that what you want? Show us the circuit. It seems to me that the voltage divider is overwhelming the 1M resistance across the capacitor. Bob
  16. BobK

    Simple transistor circuit problem

    You would be far better off using microcontrollers for this. One microcontroller could control many LEDs and having a single reset and fade control would be trivial. Bob
  17. BobK

    Band-Pass Filter Help

    Active filters are the only way to go. You get 12db / octave for each stage, and need only resistors and capacitors (and op amps) to implement. Here is free software to design active filters. http://www.ti.com/lsds/ti/analog/webench/webench-filters.page Bob
  18. BobK

    New Programming Language Anyone?

    When I said C was not well suited for programming micros, I was not thinking about Basic as the alternative, I was thinking about Ada. Ada was designed for embedded programming and does support fixed point numbers and multi-tasking. And it does these in a way that they can be implemented very...
  19. BobK

    Looking for transmitter

    Yes, figure out a different way to do this. Signal strength is not a reliable measure of distance. Bob
  20. BobK

    Battery Charging Problems

    If you must charge from 48V and use PWM, use an inductor after the PWM signal and you will have a buck converter. Bob
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