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  1. Alec_t

    Pulse circuit current control

    You can't with it wired as shown! You will also fry the micro if you put 9V on its output pin.
  2. Alec_t

    Re-wiring a 3v hand-fan to run off a USB cable, need help reducing voltage.

    What current-rating/type of diode? A 1N400x series type (1Amp rating) should be ok.
  3. Alec_t

    Mini self powered generator

    You shouldn't believe everything you see on Utube ;). There are all sorts of spoof videos.
  4. Alec_t

    Re-wiring a 3v hand-fan to run off a USB cable, need help reducing voltage.

    .... or use 3 diodes to drop about 2.1V.
  5. Alec_t

    Pulse circuit current control

    Your pot seems to be "back-to-front". The + input of the op-amp is at a fixed 9V, so the opamp output will be fixed at a bit less than 9V.
  6. Alec_t

    Limit input voltage for constant A/C supply?

    Does your guitar amp really need as much as 100V DC?
  7. Alec_t

    4xLCD torches in series without using 4 lots of 3xAAA's

    Welcome to EP, Joel! Do you know the LED wattage? I would be concerned about the health hazard of using 4 UV sources.
  8. Alec_t

    Re-wiring a 3v hand-fan to run off a USB cable, need help reducing voltage.

    Without knowing how much current the fan draws (a) when running at normal speed and (b) when stalled it is difficult to specify a suitable resistor value. Using a series resistor (fixed or variable) is not a good way of controlling motor speed. The problem is that (counter-intuitively) on...
  9. Alec_t

    Change a microwave dial into a keypad?

    Welcome to EP, Nathan! The dial is just a rotary mechanical time-switch (Google should be able to find you some examples). This isn't what you want to hear, but I would caution against messing with a microwave oven. It produces enough microwave energy to KILL you, or cause a fire if the control...
  10. Alec_t

    Need Help With My Flying Motor Project!

    Be aware that long thin wires may have such a high reistance that they will drop several volts, leaving few volts to drive the motor. That may account for the lack of lift. Even if you could generate enough lift, have you considered how to cope with the counter-torque which will try to spin the...
  11. Alec_t

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    One way to increase a pendulum's period without changing the pendulum length is to make the plane of rotation non-vertical (Google "horizontal pendulum"). Unfortunately the mechanism you show doesn't allow that principle to be applied without drastic modification :(.
  12. Alec_t

    Help getting my circuit to work - sound card osciloscope calibrator

    Good result!
  13. Alec_t

    frequency range too small on 555 timer circuit?

    You're probably thinking of my 'Simple PWM' article over at ETO ;).
  14. Alec_t

    frequency range too small on 555 timer circuit?

    Here's what's going on :- R1/R2/U1a/U1b form a large-hysteresis Schmitt trigger circuit with an inverting node at U1a output. C1 and the SetFreq pot then turn this into a square-wave oscillator. The waveform across C1 is approximately triangular and is summed (via R3/R4) with a voltage set by...
  15. Alec_t

    Help getting my circuit to work - sound card osciloscope calibrator

    Because of variation of the Vbe of Tr1 with temperature, the circuit is far from ideal as a calibrator. A TL431 adjustable reference voltage source could be used in a more accurate/stable supply for, say, an oscillator based on a CD40106 Schmitt inverter.
  16. Alec_t

    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    I agree with duke 37 (post #2). That circuit does not control frequency; only whether or not the pendulum oscillation keeps going.
  17. Alec_t

    electronic tube

    Do a bit of googling and see if any are for sale.
  18. Alec_t

    simple control a dc motor via arduino uno ?

    So that the high back-emf voltage is clamped to the supply voltage and to provide a re-circulating current path to enable energy stored in the inductor to be dissipated.
  19. Alec_t

    simple control a dc motor via arduino uno ?

    Without that diode the transistor will die.
  20. Alec_t

    Mic detection circuit

    1) Whether or not the current will change when you flip the mic switch will depend on how/where the switch is wired (which we still haven't established). 2) Passing ~2mA DC through the mic coil, or through its impedance transformer if fitted, may result in distorted sound. 3) The 10uF cap will...
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