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  1. duke37

    Can you build your own TV aerial?

    We have aerials in the UK, I thought they have antennas in the US. Any bit of wire will pick up a signal, even a guitar, but the aim is to get as strong a signal as possible with as little noise as possible. In order to do this you will need a BIG aerial high up above surrounding obstacles...
  2. duke37

    Temperature Sensor

    I recherged my brain cell overnight. A simpler way of connecting the leads is to place them in antiparallel and put a resistor in series, then connect between 741 output and 0V. Each led will protect the other from excess voltage. You will be stuck with a similar current in each led which...
  3. duke37

    Temperature Sensor

    You will need to reconnect the op-amp as a comparator. Remove the resistors on the amp Place a potentiometer from ground to 6V with the slider connected to 741-.. This will provide a temperature set point. Put a diode (1N4148) and resistor in series with each led and connect one between the...
  4. duke37

    What determines RPM speed of Electric motor?

    The faster you spin, the more the centrifugal force. There is a limit to the stress for all materials. Perhaps a carbon fibre wound rotor would be best? A car dynamo became obsolete partly beacause its speed is limited, run them too fast and the windings fly off. The alternator has the...
  5. duke37

    What determines RPM speed of Electric motor?

    I suggest you go to Iran and get details of their centrifuges. Dynamic stabilisation is a problem. You will need air or magnetic bearings and a very strong rotor that will not explode under the centrifugal forces.
  6. duke37

    10 amp NPN Transistor switch circuit

    44V on the gate of a mosfet may be too high. You would need a resistor and a protective zener to limit the voltage to, say, 15V.
  7. duke37

    Op-Amp Filter Circuit Transfer Function

    Are the feedback components connected in parallel rather than in series?
  8. duke37

    Schmitt trigger

    Three comments The 7k and 6k resistors do NOT give negative feedback, it is positive. You may have popped off the red led. There is a limit to the reverse voltage which a led will stand. Since you have plenty of voltage available the best way of protecting them is to put a diode in series...
  9. duke37

    centre tap rectifier

    At low voltages, the 1.2V or so drop in a bridge rectifier is significant so a centre tapped transformer winding is used with only two diodes. The voltage drop is reduced to 0.7V or so at the expense of a slightly bigger and more expensive transformer At high voltages the diode voltage drop...
  10. duke37

    Micro-controller controlled Spark plug

    The coil needs to be 'charged' in between the sparks, to do this at high speed, a low inductance is required and a resistor is used to define the current and limit the dissipation in the coil if the engine is not started and left with the points closed. There were problems with 'sports' coils...
  11. duke37

    Micro-controller controlled Spark plug

    The capacitor (condenser) in the early systems was there to give a delay so that the points had a short time to open before the high voltage occurred, thus protecting them from sparking and destruction. A better system was the capacitor discharge system whereby a capacitor was charged to 300V...
  12. duke37

    How to remove hum from car cassette adapter

    To reduce common mode currents, simply take the cable which should be shielded, and pass it through the ferrite ring several times. You may be better to drive to warp number one only or even turn off the noise and concentrate on driving.:):)
  13. duke37

    Micro-controller controlled Spark plug

    Yes, go for it, you will learn a lot. A 12V source and an old 12V coil will be the way to start.
  14. duke37

    Micro-controller controlled Spark plug

    Once again, you are getting to the limit of my knowledge. I have never met a 1kV ignition coil, I played with transistor driven coils many years ago. The coils then had a ratio of 1:20 or so, thus 300V on the primary would give 6kV on the secondary. The coil should be protected by a spark...
  15. duke37

    Tube amp acting very strange-- tubes acting as speakers

    But an electric guitar pick up coil may just do the job.:):):)
  16. duke37

    How to remove hum from car cassette adapter

    The whine is possibly due to the alternator which varies in frequency with the engine speed. If the hum is due to the ignition, that should also vary with the engine speed. Shielded wires would help. Winding the connecting cable on a ferrite core may help but it is all trial and mostly error.
  17. duke37

    Micro-controller controlled Spark plug

    I know little about computers. Either circuit will work, the plug will spark when the transistor is switched off. PWM will give multiple sparks if there is enough time to attain the required primary current. There should be a high voltage (300V) zener across the transistor to limit the...
  18. duke37

    220V voltage to digital voltage

    I do not think that a diode across the zener is necessary but it will not hurt, the zener will do the job.
  19. duke37

    Variable power supply for supplying valve amp builds

    I suggested a switched potential divider instead of a sliding potentiometer since the voltage is so high. You could use a pot if you could find one fat enough. If you use a tapped resistor chain with a switch, make sure the resistors and switch are capable of the duty. If you use 10k...
  20. duke37

    Identify this component

    !974 old? What about 1924? If you can find the make and model of the radio you may be able to find a circuit diagram (schematic) and work out what inductance is missing. The next problem will be to find a substitute if you wish to repair the radio. It may be an intermediate trnsformer or...
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