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  1. BobK

    Beginner pull up resistor question

    Ach! I wasn't expecting you to use an old analog voltmeter. If you had used a digital voltmeter, it would have read very close to 5V, probably 4.99. That is because the typical modern digital voltmeter has an input resistance of 1M. It looks like your analog VM had an input resistance of...
  2. BobK

    Coulomb's Law in practical life!

    No net charge outside the capacitor, but the plates will have equal and opposite charges, so they will attract each other. Remember though, the for large capacitors, the kind that might hold a Coulomb of charge, this is distributed over a huge area. Bob
  3. BobK

    Quick Question About a Transistor

    Well, you have just invented the diode! Actually the Zener diode with about a 6V reverse breakdown. Bob
  4. BobK

    Need to switch an ATX power supply every 20 min...

    Presumably, there is a switch connected to the motherboard via a header that is used to start it up. This is where you should connect. No need to cut any wires at all. The transistor can even be wired in parallel to the switch and either one will start it up. Bob
  5. BobK

    LED Push Button Dimmer

    You could get this programmer and demo board from Microchip: http://www.microchip.com/Developmenttools/ProductDetails.aspx?PartNO=DV164130 Get that, and a 10F320 in PDIP, which will plug into that board, and you will have everything you need to write the code. It comes with tutorials to help...
  6. BobK

    Slow down this circuit's oscillation

    As Gryd3 said, like this: (excuse my amateurish painting)
  7. BobK

    Coulomb's Law in practical life!

    The wires have no net charge. The force between them comes from magnetic force which is a different formula. Bob
  8. BobK

    Slow down this circuit's oscillation

    Instead of the lines going from the two Outputs to the inputs of the ANDs, try putting a resistor between them, then a capacitor from the input to ground. That should slow it to something on the order of RC seconds of on / off time. Bob
  9. BobK

    LED Push Button Dimmer

    Sounds to me like you are bipolar. Perhaps some Lithium would help. Bob
  10. BobK

    Beginner pull up resistor question

    Think of the microcontroller input having a 5 Meg resistor connected to ground. This would cause 1 uA to flow when connected to a source of 5V. This is not actually the case, but it should help you visualize what is going on. Let's look at it another way. Connect 1 end of a 10K resistor to...
  11. BobK

    LED Push Button Dimmer

    Do not fear. We still need discrete transistors when currents of > 20mA are required. Until they come out with a uC with power MOSFET outputs... Bob
  12. BobK

    stepper motor is missing the steps

    I don't understand. Why are you using PWM with a stepper motor? What is the PWM supposed to control? Bob
  13. BobK

    Beginner pull up resistor question

    Here is what I think you are missing. There can only be a voltage across a resistor if there is current flowing through it, according to Ohm's law. With a 10K resistor connected to 5V, the other end will read 5V as long as there is no current flowing. If there is current flowing it will...
  14. BobK

    LED Push Button Dimmer

    The Microchiop PIC10F320 could easily do what you want and costs 42 cents qty 100. It comes in a SOT23 package, which is about as small as you could want. Or, if you don't want to deal with surface mount you can get it in a DIP-8 for 50 cents. There are even cheaper ones that would also...
  15. BobK

    LED Push Button Dimmer

    In that case, you would save a lot of money by using a microcontroller. The entire circuit would be the micro (about $.50), the switch, one transistor, one resistor, and one capacitor. Smaller board area and less component cost. And far more flexible. Simple changes in programming could...
  16. BobK

    Decreasing voltage to motor

    Only if the motor needs to be reversible. A single MOSFET will work otherwise. Bob
  17. BobK

    LED Push Button Dimmer

    Simplest way is to use a microcontroller. Bob
  18. BobK

    Ultrasonics

    Well, he was a member of the Rat Pack. Bob
  19. BobK

    DipTrace PCB software

    Can it produce Gerber files? Bob
  20. BobK

    Where to Put Ground on PCB

    It looks to me like the - is ground, and the resistors are already configured as a voltage divider which is variable depending on which switches are on. What would you do with the "ground" you want to add? Bob
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