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  1. BobK

    Infrared Obstacle Detection

    I have no idea what you are asking. The link you give is for an obstacle detector that outputs an analog signal to be read by a microcontroller. It has nothing to do with a servo. Bob
  2. BobK

    Trying to make analogue sound to lcd?

    Yes, I do, because there are no spirit voices to tap. What else could they do? Bob
  3. BobK

    Op Amp HiFi Project

    Not really, as I haven't tried any of them. Really old as in paper cone? Those speakers do not age well. You would be better off to buy a new one. You will not get much volume out of an MP3 player without using an amp. Bob
  4. BobK

    Simple transistor circuit problem

    Another thing to consider. I know you want smooth brightness control. This becomes more difficult when combined with multiplexing and also becomes an issue when you try to drive too many LEDs from one micro, no matter how it is done. \ The micro needs be able to turn on the LEDs 100 times...
  5. BobK

    need help to understand a circuit

    This is the standard arrangement for a push-pull amplifer. As Duke said, the diodes help mitagate a problem where neither transistor is turned on. This is know as crossover distortion. Bob
  6. BobK

    Op Amp HiFi Project

    You might be just as well off to buy an completed audio amp module from Ebay. They can be quite inexpensive. Bob
  7. BobK

    disadvantages of 2.4 GHz wireless module on human body

    No, it is not harmful. Bob
  8. BobK

    Trying to make analogue sound to lcd?

    My guess is they randomly output a recorded word. Bob
  9. BobK

    Op Amp HiFi Project

    You cannot use an op amp to drive a 4 Ohm speaker. You want an audio amplifier IC instead. And you won't get much power from 3.3V at 160ma. That is a little more than 1/2 W and an amplifier (unless it is class D) will be about 50% efficient, so about 1/4 W is all you can hope for. Bob
  10. BobK

    Illogical Transistors

    Because the base to the collector is a diode, as is the base to the emitter. The base is the anode of each in a NPN transistor. In fact that is where the NPN comes from! Bob
  11. BobK

    DIODE

    That configuration is used to limit the voltage to a little below ground and a little above V+. Bob
  12. BobK

    Band-Pass Filter Help

    An opamp has a parameter called the GBW gain bandwidth product, expressed as a frequency. This is the frequency at which the gain has fallen to 1, If you want to get a gain of 750 for audio frequencies of up to 20KHz, you would need an opamp with a GBW of 15MHz. I don't know what an LM324 is...
  13. BobK

    Resistor diode arrangement

    That is the null circuit. It does nothing. Bob
  14. BobK

    Band-Pass Filter Help

    Well, why didn't you tell us that before I went off and designed one? It would really help if you would not mislead us. So, what do you want the -3db point to be? Bob
  15. BobK

    Band-Pass Filter Help

    Here is a filter design that meets your specs, designed based on the multiple feedback filter on the page I linked you to. It wasn't so hard after all. I have to wonder why the programs did not handle it. The specs I used are 20Hz center frequency 100Hz 3db point, and the graph looks like it...
  16. BobK

    Band-Pass Filter Help

    I think Laplace had the right idea. I tried another filter design tool and the problem is the large pass band you want. These 2nd order active filters fall off too fast to do that. Here is a tutorial that shows how to use a low and high pass filter together to produce a wide passband...
  17. BobK

    Increase resistance in a circuit by a percentage

    An analog way might look like this: 1. Run a fixed current through the sensor to convert to a voltage. 2. Amplify this voltage via an op amp. 3. Use this voltage to control a current source connected to the meter. I have no idea whether this is workable or not :) Bob
  18. BobK

    PIC16F877A - PWM Sine wave coding problem

    The code looks OK to me. I did not check all the bits in the register inits, but the logic looks fine. You don't need to use ints for a and di, they can both be chars and avoid the 16-bit arithmetic, but that should not cause any problems except making it slower than it could be. I don't...
  19. BobK

    Audio Signal ADC

    Well, it sounds like you have too much amplification. Have you looked at the voltage out of the op amp buffer (of course, it should be the same as the input). If it is greater than the range of the ADC, you would need a divider, or to reduce the gain of the preamp. Bob
  20. BobK

    Current Surge

    Looking good, I am glad I could help. My very first project after years neglect to my electronics hobby, was a micro controller buck converter NiCad charger. Bob
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