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  1. BobK

    Profitable circuits

    Profitable circuits for hobbyists are ones that are not mass produced in China. If you can buy it at Walmart, it is unlikely you can build it for less money without skimping in some way. Bob
  2. BobK

    Stepper Motors. Any Experts?

    I give up. Bob
  3. BobK

    Does this Circuit make sense?

    That is becuase you are using the hydraulic metaphor incorrectly. There are no leaks in the system (a better plumber than I must have put it together!). The flow of water in a series of connections is always the same, the pressure can change as it goes through different devices, but not the...
  4. BobK

    Different soldering techniques

    I was thinking about another kind of joint, the kind where one might wet one's whistle. And no, crystalline solder is not one of my favorite beverages! Bob
  5. BobK

    IR activated switch

    You are a little ahead of yourself. Generic Electronics Project Plan 1. Specification. 2. Design. 3, Parts selection. 4. ... You are at 3 without having completed 1 or 2. Bob
  6. BobK

    Different soldering techniques

    Yeah, like what would be the point of a dry joint? Bob
  7. BobK

    Question about using a micro-motor and voltages

    If you want 35ma at 0.8V, all the rest of the voltage goes to the drop in the resistor. Use Ohm's law: E = I R (8.4-0.8) = 0.035 R 217 = R So probably start with a 220 Ohm resistor. Then calculate the power requirement for the resistor: P = V I = (8.4-0.8) * 0.035 = 0.266...
  8. BobK

    Question about using a micro-motor and voltages

    Actually more than that. At 60ma the forward voltage is only about 0.7V, so more like 9 or 10 to drop the voltage to 1.6. A single resistor of about 120 Ohms, 1 Watt should work. Bob
  9. BobK

    simple circuit won't work..

    Yep, I got twenty turns without overlap. Bob
  10. BobK

    IMU pins help

    Yes, it will. Look at the schematic and it shows what each of the pins is connected to. RAW is the input power. The other pins are all connected to pins on one of the two chips with the same designation. Bob
  11. BobK

    Does this Circuit make sense?

    The "forward voltage" across an LED is called that because it refers to the voltage at a specific current in the forward direction, i.e. with the anode at a higher potential than the cathode. A diode would also have a "reverse voltage" which would be different at a given current, and would...
  12. BobK

    Stepper Motors. Any Experts?

    So now you link to a video where a motor is being used as a generator. Don't you think it would have been helpful if you had mentioned before that you wanted to use this as a generator, not as a motor? Bob
  13. BobK

    simple circuit won't work..

    That looks like too few turns to me. My joule thief has about 20 turns of enameled wire on a similar sized toroid.
  14. BobK

    Two divided by zero (superconductors)

    There cannot be a 2V potential drop across a superconductor, it is always 0. As you surmised any current will be limited by the external circuit. Bob
  15. BobK

    Small pre-amplifier K8084

    Well, the transformer was already marginal, having exactly the same current capability as the amplifier's requirement. But, if you are not going to be using the amp at full volume you should be fine. Bob
  16. BobK

    difference in parameters when circuit switched on and when switched off

    A resistor drops the voltage only when current is flowing though it. This is explained by Ohm's law: E = I R When E is the voltage across the resistor, I is the current, and R is the resistance. If you make I = 0, you can see that E is zero, which is why your meter reads 12V when a...
  17. BobK

    Quick Easy Circuit Question (LED)

    If you are using a coin cell, even the large CR2032, you will not have to worry about taking it out after 2 Hours, it will already be dead! Bob
  18. BobK

    Controlling large motor with MOSFETS

    Some microcontrollers have a fault input that shuts down the PWM immediately without any program intervention. This would be a good way to shut down on over-current. Some also have built in comparators, so you might save a lot of circuitry by using those two features. Bob
  19. BobK

    Ohm's Law or not Ohm's Law... That is the question

    If you can show me how Ohm's Law: E = I R, where R is a constant, does not give the relationship of the voltage across and inductor and the current through it. Period. If you can show me otherwise, please do. Laplace demonstrated that a whole family of equations involving mathematical...
  20. BobK

    Stepper Motors. Any Experts?

    No, I don't think you do understand. The RPM will depend only on the frequency of the pulses. If you don't apply pulses the RPM is zero. Each pulse (actually sequence of pulses to the different phases) rotates the shaft 1.8 degrees. If you apply 200 pulses per minute the RPM is 1, because the...
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