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  1. BobK

    SPI ADC/DAC with 8051

    The difference between SPI and an ADC is like the difference between a highway and the two cities at each end of it. The highway gets you from one city to the other. SPI gets data from one device to the other. Note that all of these are analogous: There isn't necessarily a highway between the...
  2. BobK

    Charging NiMh battery pack with BQ2004

    Actually, I now remember that the voltage divider has resistance in the hundreds of K. The multimeter is probably 1Meg input resistance, so you will not get an accurate reading. The Thevenin resistance is 1.04K, So if the meter is 1Meg you are getting a reading that is about 10/11 of the...
  3. BobK

    Problems with using LM324 as an inverting amplifier

    Okay, so my post is not what you wanted. Use an opamp with dual supplies, as AK said. Change the + input to go to ground, instead of the voltage divider in my circuit, and you are done. Bob
  4. BobK

    Arduino Sound generator wanted

    The trick to getting non-square waveforms out of a microcontroller is called PWM. To get audio signals up to 20 Khz, you would need to use at least 50KHz as the PWM frequency, 100KHz would be better. The PWM period is changed over a cycle of the designed waveform to match the voltage at that...
  5. BobK

    Charging NiMh battery pack with BQ2004

    Those numbers cannot be right. If the battery voltage is 19.83 then Vbat should be 18.83 / 7.5 = 2.57. Are you sure about the resistances in your divider? Bob
  6. BobK

    Energy from the air

    Great idea. It could capture a lot of energy during a lightning strike. Bob
  7. BobK

    Problems with using LM324 as an inverting amplifier

    Assuming you mean a pulse that goes from 0 to V. You can invert a positive going pulse by using a transistor and two resistors. Same circuit can also change the level of the high portion of the signal. You can also do it with a single supply opamp. You will need to bias the + input to half...
  8. BobK

    Battery booster

    Sorry, I was asking the OP for a link. Edited to add a question mark. Bob
  9. BobK

    Battery booster

    Link? They may have a limitations on output current that make them unsuitable. Bob
  10. BobK

    Square wave signal with ADC converter

    You are far from clear. I have no Idea what “a fixed width of 0 to 5V” means. Volts is not a measure of width, and 0 to 5 is not fixed. “Variable frequency” I can understand. “Convert it to a continuous signal” again has no clear meaning. If I output a steady 5V I would meet that...
  11. BobK

    N channel Fet v npn

    Did you mean MOSFET, as everyone seems to assume or did you mean FET. They are two different things. FET usually refers to a junction FET or JFET. A typical N-channel JFET requires a negative voltage to turn it off. Bob
  12. BobK

    Square wave signal with ADC converter

    If you are trying to measure something, something ought to be varying. You have not told us what. It might be the frequency, the peak voltage, the duty cycle, or something else. So, what are you trying to measure? Bob
  13. BobK

    Measure current with strange output

    For the voltage you need a votage divider with two resistors in a ratio of 9 to 1. For the current a 0.01Ω resistor would work but it would dissapate 100W of the current is 100A. A hall effect current sensor, probably coupled with an opamp to adjust the output range. Bob
  14. BobK

    How to build a 15,000 Gauss hand-held electromagnet

    You get the strongest field with a nearly closed magnetic circuit with only a small gap, which is where the field wiill be strogest. What do expect to do with this magnet? Bob
  15. BobK

    How does a switch mode amplifier... amplify?

    Do you know how a switch mode power supply works? If so, a class D amplifier is nothing more than a switch mode power supply whose output voltage follows an audio signal. The key is switch mode. A transistor used as a switch amplifies a digital (on or off) signal. Using a MOSFET (which any...
  16. BobK

    Buck circuit to output of solar panel

    I think what you want is an MPPT (maximum power point tracking) controller. It constantly adjusts the current drawn in order to extract the maximum power from the solar panel. Bob
  17. BobK

    Arduino restarting while controlling a mosfet with PWM.

    In the case of the motor, do you have a reverse biased diode across the terminals the suppress the voltage spike whenever the motor is turned off? Also, the physical wiring can have an effect. The wiring from the supply to the the microcontroller should be separate from that to the load. If...
  18. BobK

    Adding a timer somehow to a 12v solenoid

    More likely you wired it incorrectly. The relay's common and NO contacts should be wired across your original switch. Bob
  19. BobK

    Constant current LED drivers - faulty, flashing panels

    Let me rephrase. How did you pick this driver for the this LED panel? The way one would ordinarily do that is to know the rated current and forward voltage and then pick a driver that is compatible. How did you do this without knowing the forward voltage? Bob
  20. BobK

    Constant current LED drivers - faulty, flashing panels

    Guessing isn't good enough, it must be within the range of voltages specified by the driver. You can power it on on a working driver and measure the voltage across it with a voltmeter. You should also check the current. If the current is not the rated output current or the voltage is out of...
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