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  1. BobK

    Batteries and Power Adapters

    maH is a measure of capacity, i.e. how long a battery will last before it is depleted. There is no equivalent for a mains power supply. The right question what voltage and current are required by the load you are trying to power. The voltage must be the same and the current capability of the...
  2. BobK

    MCU in series with LED

    Well, that would depend on the LED and the MCU. All but the highest performance PICS draw less than a few milliamps. Bob
  3. BobK

    Newbie question

    It has circuitry that switches from charging to discharging after a set voltage is reached. Bob
  4. BobK

    need help with timing issue on an astable

    I think that is expected, because the capacitor has to charge from 0V to 2/3 Vcc instead of 1/3 Vcc to 2/3 Vcc. The output of the logic gate is probably not high enough to power the '555 reliably. Bob
  5. BobK

    Battery powered quick flashing LED

    A battery + capacitor + LED does not make a flasher. Here is a tutorial thread the covers building an LED flasher. https://www.electronicspoint.com/building-device-schematic-yet-another-work-progress-t256843.html Bob
  6. BobK

    Timer

    So you need 3 things. A timer that pulses every 3 - 12 seconds, adjustable. A method of detecting when the disc is at one of the 12 positions. And a control circuit that runs the motor. The first is easily done with an NE555 timer chip. You might even be able to find one that would be...
  7. BobK

    Timer

    Okay, so in that video, what I see is that the disc simply waits several seconds then automatically advances to the next station. Is that what you are looking for? Does the wait time need to be adjustable? Bob
  8. BobK

    Measuring High Input Voltages

    Do they share a common ground? If so, a voltage divider might be all you need. Bob
  9. BobK

    Interference into amp from LEDs

    It might be simpler to just run the ampliifer off a different power supply. A 9V battery for instance. Bob
  10. BobK

    Timer

    I don't think you are going to find a ready-made solution. Either concept is best implemented using a microcontroller which involves not only circuit design but programming as well. Not a project for a beginner. How do you envision opearting the device? Is there a rotary switch to select...
  11. BobK

    Timer

    A stepper motor moves in discrete, repeatable steps. So if you once know how the disc is poisitioned, you can calculate how many steps to advance, in which direction to get to the desired position, then perform that number of steps. You would need some method of finding one specific position...
  12. BobK

    MOSFET Switch not Working

    Take out R18 and R22 and connect the gate directly to the collector of Q5. Also, you must have some load on the drain of Q6 in order to make a measurement of it's voltage meaningful. Bob
  13. BobK

    Definitions for op amps?

    Okay, I have got it. Use the differential configuration (here) http://en.wikipedia.org/wiki/File:Op-Amp_Differential_Amplifier.svg And set all R the same. V2 is your input, V1 is set to 2V and you get your input (4-6) - 2 = (2-4)V out. Bob
  14. BobK

    Definitions for op amps?

    Actually, my solution above would not work. You cannot do it because a non-inverting amplifier cannot have a gain of 1. There should be a way to make a difference ampliifer to subtract 2 from the input, but I am failing at coming up with the right configuration. Bob
  15. BobK

    Definitions for op amps?

    removed, incorrect solution. Bob
  16. BobK

    watt

    Haven't been on all day, I still Ninja you by 1 minute. You'll get me next time, I'm sure. Bob
  17. BobK

    watt

    There is no such thing as a 3 Watt battery. Battery capacity is measured in Amp Hours or Watt Hours. Bob
  18. BobK

    help with counter

    I presume you are using a 4017. You could use a separate SR flip-flop that latches to 1 after the first clock pulse by feeding Q back to S. Then AND that signal with the 0 output of the 4017. Bob
  19. BobK

    Wireless trigger for LEDs and buzzers

    You need an additional CONFIG setting for FOSC. Bob
  20. BobK

    Wireless trigger for LEDs and buzzers

    The default configuration for the PIC16F627A is to use an external RC oscillator. You need to set the FOSC config bits to select the internal oscillator. Bob
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