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  1. duke37

    Programmable Interval Power Timer for Bubble Machine

    Kris, Yes, its for you, I looked at the end of the thread, I did not realise that you had hi-jacked it. You do not need to modify the toaster, you will need to put the thermostat in a properly insulated box but that will be no more difficult than making a box for your circuit. Duke
  2. duke37

    Clap clap switch

    It is up to you to define what a double clap is, I would suggest that it is a double clap if the second clap arrives within a second of the first clap. I do not have the time to design a circuit, you need to generate a block diagram to define what you want to do and then design circuitry to...
  3. duke37

    Clap clap switch

    That circuit looks to me to be one clap for on and the next clap for off. If you want it to respond to a double clap then a considerable amount of extra circuitry will be required and you will have to define what a double clap is.
  4. duke37

    How to calculate the value of Zin and Zout???

    Zin consists of 47k in parallel with 1n. Below about 4kHz the resistor will predominate and above this frequency, the capacitor will predominate. In addition there will be loading due to the transistor, since this is swtching, I would not know how to calculate its input impedance. In a...
  5. duke37

    Programmable Interval Power Timer for Bubble Machine

    A standard thermostat control as used for hot plates will do what you want and go from 0% to 100%.
  6. duke37

    Diode when wet

    I do not think it possible to answer your question. The rate of corrosion will depend on many factors. The wires may last minutes or months. I suggest that you change any components which have corroded leads. I have seen the leads breaking off transistors close to the can. I use Waxoil which...
  7. duke37

    How this ps unit works??

    It will be gradual to give proportional control.
  8. duke37

    Increasing motor's RPM + Torque with stronger magnetic fields?

    If there is no change of speed, there will be no effect of inertia. Force = Mass * Acceleration Torque = Inertia * Rotary acceleration If the speed is constant the torque depends on the load and the motor current depends on the torque.
  9. duke37

    Additional pass through transistor or bigger reg?

    The bridge rectifiers must be connected correctly. It would be better to rotate the diode symbol a quarter turn to the left.
  10. duke37

    amplifier question

    Power is proportional to the square of the voltage. W = V*V/R
  11. duke37

    transistor circuit for counting wheel rotations

    Won't you need a lot more than 3V to fully turn on the mosfet?
  12. duke37

    30vDC to power 3 12Vfans

    If the fans are the same, just try the three in series. Each will then have 10V.
  13. duke37

    How does a satellite transmit data?

    No, sound is a pressure wave not an electromagnetic wave. Electromagnetic waves can have a very wide range of frequencies. Transformers use low frequency waves but need a magnetic core for efficiency. As frequency rises we go from long wave, medium wave and short waves and eventually get to...
  14. duke37

    How this ps unit works??

    The transformer and D1,D2 provide a rough DC across C1. Q2 and Q4 are emitter followers so the voltage at Q4 emitter will be 1.2V (two diode drops) less than the collector of Q1. R2 pulls this voltage high. Output voltage comes through R5 and a proportion of this, set by P2, feeds the base of...
  15. duke37

    Diode when wet

    Water will conduct at any voltage if it is not pure. Pigeon poo does not help! If conduction occurs it may upset the operation of the gubbins but will also give electrolytic corrosion which can give all sorts of problems. Transistors do not work very well with only two legs, so keep it dry.
  16. duke37

    What value of resistors do I need and a sanity check

    This seems to be a constant current power supply with switched output range. The leds will need a voltage to work which will completely ruin the supply. If you want an indication of what you are doing, use a switch with another pole to select a led independent of the control circuit. Are...
  17. duke37

    Phase Shift Oscillator Design Help

    Phase jump. It is just to fit on the graph. Once round the circle is the same as starting again.
  18. duke37

    Help! High current DC welding bridge rectifier

    The arc is struck by shorting the output of the welder, developing a high current and then opening the contact and with the internal inductance gives a high voltage. Your diodes must withstand both of these conditions. Overvoltage could kill the diodes quickly but diodes can take an over current...
  19. duke37

    Repair Wharfedale speakers

    Did they click when the meter was connected, if so, they look good. Have you checked the inductors for continuity? The most likely fault is the capacitors. these are unusual, they are non-polarised electrolytics. They should be replaced with the correct values. I have a pair of Wharfdale...
  20. duke37

    Repair Wharfedale speakers

    I am not familiar with the various Wharfdale models. What is the model? How many drivers in each speaker? I would suggest that you take a photo of the connections, then disconnect one wire to each driver and measure the resistance of each driver. If you use a low resistance range on an...
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