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  1. duke37

    Quick transformer question

    If you want DC, connect the two windings in series and place a bridge rectifier across the total 18V. The 18V is available from the bridge rectifier and 9V from the winding centre tap.
  2. duke37

    find the answer

    You are right. When no current flows through the resistor, what is the voltage across it?
  3. duke37

    MOSFET Help

    The FET does not need current other than to turn on and off. It behaves as a capacitor. A gate resistor is used to stop high frequency oscillation during the transition time, 100 ohm is often used. Too high a resistance will slow the transistion to an unacceptable level. To drive a light...
  4. duke37

    IGBT ignition coil driver

    You are looking at the right thing, the threshold voltage is where the device just starts to conduct. There will be enough current to drive a voltmeter but not to do any useful work. The data sheet shows a graph giving the gate votage necessary for the required output current.
  5. duke37

    IGBT ignition coil driver

    It looks as if you do not have enough drive voltage, at least 6V, better 8V, 10V good.
  6. duke37

    MOSFET Help

    The load is on the drain of the FET. The rectifier will give 170V rectified. This is a bit much for the gate of the FET!!! If you have a common negative line, there is no need for an optical isolator. You could drive the FET directly from the 555 which would limit the gate voltage to 12V...
  7. duke37

    comparator as a switch to 8051

    Try disconnecting the 8051 and see if the output goes high. Harald is probably right. Split the problem, get one piece working at a time.
  8. duke37

    comparator as a switch to 8051

    You could try dropping R100 to 1k, the 339 will be able to manage this and will provide stronger pull-up.
  9. duke37

    find voltage across diode

    :) Where did the smoke come from? :):)
  10. duke37

    Notifier for diff locker off

    Harald, I think he needs it the other way round, i.e. the circuits should activate when the light is out. I think a changeover relay with the coil connected across the bulb would do, using the back contact. Duke
  11. duke37

    find the answer

    1. There are two answers since you have two resistors. Find the total resistance. Calculate the current using Ohms law. Calculate the voltage across each resistance using Ohms law. 2. How much resistance will an ideal inductor have? (It is all at DC) 3. How much current will...
  12. duke37

    Microphone doesn't work but standard output audio works

    I am too old to know abbout all this modern tackle, however, audio signals are normally sent from one instrument to another with about 0.5V (500mV). Magnetic microphones give out about 5mV, so are your levels right. What is the output level of the iPad and what is the output level of the...
  13. duke37

    A few quick questions

    47 ohm in a signal circuit seems very low to me. Would 47k be better?
  14. duke37

    Connecting a power supply and battery in paralell

    I was under the impresion that a 12V battery should be charged at 13.8 to 14.4V. Your big charger will do this and will not overcharge. If you leave the battery charger connected when driving the invertor, the battery voltage will fall and the charger will try to maintain it. The invertor...
  15. duke37

    DOORBELL circuit / project

    I doubt if it is the speaker. What circuit are you using to drive it?
  16. duke37

    lottery wheel

    The 555 variable frequency oscillator looks good. Describe what you mean by a shooting star and a falling star.
  17. duke37

    battery as mic preamp?

    A carbon microphone cosists of a pack of carbon granules which are conductive. Sound vibrations alters the connections between the particles so altering the current. The output electrical power is therefore higher than the sound input power. This is the system used in early telephones.
  18. duke37

    dc-dc voltage multiplier

    I have an old Maplin catalogue which shows Aimtec convertors which look like the ones you want
  19. duke37

    lottery wheel

    The 4017 Johnson counter will give one of ten outputs in sequence. You will need some means of slowing and stopping the clock. Perhaps a voltage to frequency chip (LM331N)? Just charge a capacitor on switch on and let it discharge through a resistance?
  20. duke37

    dc-dc voltage multiplier

    Jaycar have a UK output but I have never used them.
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