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  1. duke37

    Use LED to denote current flow in AC circuit

    I think you could get away with two leds connected in inverse parallel, then putting a 300 ohm in series. The forward voltage for the led must be less than the reverse breakdown voltage of the other led.
  2. duke37

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

    A class C amplifier can have bias, either positive or negative. The drive has to be high enough to cut off the device over part of the cycle. Normally no bias is used as this is the simplest. An oscillator is an amplifier with the output fed back to the input. The loop gain must be more than...
  3. duke37

    Motor control diy

    Small very high speed motors will take a lot of work to fit up. They will need a gearbox. I suggested in #5 that a car window winder would be suitable. It is quite powerful, about the right speed, has distance limits and runs on 12V for safety. An alternative motor can be obtained from a car...
  4. duke37

    Bicycle Turn Signal Electronics needed.

    Here is an alternative using a 4093 CMOS chip. Note that neether of the light connections go to the frame. If you pot the circuit in resin, put tails on the wires where they enter the resin so that they do not break there.
  5. duke37

    Motor control diy

    Running components above their specfication is not good. How are you going to reverse an AC fan motor?
  6. duke37

    Bicycle Turn Signal Electronics needed.

    If you are hard wiring the lights, this will be very simple. You could use a 555 or a 4093 to make an astable. Then you will need an amplifier to pass the light current. A power fet would do this. Two circuits, each activated by a button or a centre off switch would do. The main problem...
  7. duke37

    Transistor Astable Oscillator Help Please

    If you have a resistor in series with another resistor, the total resistance will be higher and the current will be lower. If you have a rsistor in parallel with onother, then extra current will flow through the additional resistor. A led needs a certain voltage to turn it on, depending on...
  8. duke37

    Lightning damage to Denon receiver--advice?

    Using your meter, measure the resistance across the power input pins. If it is open circuit, then you may, with luck, have a blown fuse and with no luck have a blown transformer. Take one logical step at a time.
  9. duke37

    12VDC Sp rocker can I use it on 24v circuit.

    If it is a standard fitting bulb, it can be changed for a 24V one. A 28V bulb would last longer.
  10. duke37

    faulty car blinker relay

    It could be a faulty connection to the bulb or a faulty ground. If the housing is broken, then the connections are likely to be corroded and so faulty. A bit of prodding and poking should be able to find the problem.
  11. duke37

    Transistor Astable Oscillator Help Please

    The multivibrator consists of two amplifiers, crossed coupled with a pair of capacitors. The base current is supplied by the 5k resistors and the collector current would normally be supplied by the 1k resistors. In your case, you have placed a LED in the collector circuit which will do the...
  12. duke37

    Transistor Astable Oscillator Help Please

    The 1k resistors in the collector circuit do nothing but increase battery drain and heat the transistors. Do as *steve* says and put a resisitor in series with the LED, 220 ohm would be about right.
  13. duke37

    Transistor Astable Oscillator Help Please

    Have you got the capacitors and transistors connected the right way?
  14. duke37

    problem with resonant frequency

    A 15MHz half wave folded dipole in free space would be about 10m long. Are you sure this was constructed on a PCB? 15% low seems a bit much but is feasible, there will be some dielectric between the parallel lines of the dipole which will drop the wave velocity. Concrete blocks are...
  15. duke37

    how to find the rpm of a motor shaft using the change in the geometry of the shaft?

    It depends on the shaft size. You can use a reflective detector with the shaft painted white/black.
  16. duke37

    Programmable Interval Power Timer for Bubble Machine

    Kris, You may be thinking of oven thermostats which have a temperature sensor. The thermostatic controls for hot plates do not have feedback, they rely on a small internal heater bending a bi-metallic strip. Harald's solution is good if you can find a dimmer with sufficient current...
  17. duke37

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

    Perhaps he did, but I doubt it. He has taken an output from Q2 emitter which will be low inpedance and coupled it to Q3 base with a small capacitor. This was probably sized to give sufficient drive to Q3.
  18. duke37

    Programmable Interval Power Timer for Bubble Machine

    Kris, That is not the specification of the original requirement. The circuit you show uses a 555 to alter the on/off times which a standard thermostat can do. The toaster will get hotter if you turn the control up and will get cooler if you turn the control down. Duke
  19. duke37

    Trying to use a Morse Key as a lamp switch

    .... .. If you use a 12V wall wart, you can use the key to switch a suitable bulb or led with no risk to life. .-.-.-
  20. duke37

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

    The 27MHz transmitter will suffer the same problem as the earlier circuit. If you load the circuit to get higher power out, then you may stop oscillation. To avoid this, add a second transistor and adjust the loading to get the output power required. The loading should be resistive equivalent...
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