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  1. duke37

    Multi Resonant Circuit

    I do not think that this can be done. A series resonant circuit with a capacitor across it will have a parallel and series resonant frequency but this will give maximumm gain in one case and minimum gain in the other. Intermediate transformers in superhet radios use two tuned circuits...
  2. duke37

    Amplitude Modulation using Op Amp.

    This is where mathematics comes into it. Modulation involves multiplying two sine waves. Sin(A) * sin(B) = sin(A+B) + sin(A-B) In othe words sidebands will be produced above and below the carrier.For normal AM, the carrier is transmitted along with the sidebands. The original low audio...
  3. duke37

    Amplitude Modulation using Op Amp.

    The diagram you show (#23) is just the addition of the radio frequency signal and the audio signal. If this is sent through a transmitter, the audio signal will not be sent and the result will be a constant amplitude carrier. You can make a modulator with a switching transistor for the radio...
  4. duke37

    Loading a Generator.

    This is not my area of expertise either. My impression is that a brushless DC motor is a stepper motor with internal circuitry to keep it going. It may be simpler to use a stepper motor. What is an out-runner? What is 235Kv, surely not 235kV?
  5. duke37

    Amplifer help!

    You could get rid of R8, R9 and R10 and connect the pot directly to the op-amp. Putting R10 between the pot and the junction of R8 and R9 would reduce the sensitivity of the pot setting.
  6. duke37

    No juice through bridge rectifier

    A bridge rectifier passes current through two diodes so you need 1.4V before it works. You could try just a single diode, preferably a Schottky (low voltage drop) instead of the bridge. Shake, rattle ond roll!:)
  7. duke37

    Rectifier circuit fails when capped.

    A transformer is rated for a certain voltage, you can use it at a lower voltage but can overstress it at a higher voltage. There are two limitations. 1.The insulation between turns and the case. This restriction will be important in high voltage equipment. 2.The limitation of the magnetic...
  8. duke37

    Rectifier circuit fails when capped.

    You must have decided on a circuit, you did not just throw components on to a board. If you have connected diodes in parallel, that is not a good thing since the hottest diode will take the most current and become even hotter. Running a transformer above its rated voltage is not good, you...
  9. duke37

    Rectifier circuit fails when capped.

    Show us the circuit, I cannot think how 9 diodes can be involved.
  10. duke37

    Impedance matching using lm324

    Your diagram shows the signal input going to - input which is connected to the output of the op-amp. There will be some fighting going on here. It is no wonder the op-amp takes excessive current. The input should go to the + terminal and this should be biased to about half the supply voltage...
  11. duke37

    Wireless RF Remote Control Kits

    They do interfere with one another. You are unlikely to have thousands of units in close proximity so the chances of interference are less. Different frequencies are used, different modulation methods and different coding. Don't operate your ham 70cm transmitter in a supermarket car park or...
  12. duke37

    Bike trainer concept I've been messing with in my head

    Yes, opening up an alternator should be fairly easy to someone who wants to build a machine. The diodes do not need to be removed but you will need a connect a wire before a diode. The cycles will need to be counted to get the distance just as they will need to be counted if you use a reed...
  13. duke37

    Bike trainer concept I've been messing with in my head

    A car alternator produces AC which is rectified to DC on its output. You could get at the AC directly to count the revolutions to get distance.
  14. duke37

    Question about antenna lengh

    The OA91 rectifies the incoming signal but there is nowhere for the current to go so, if it works at all, it will be due to leakage in the diode. The transistor can be used as a detector so the OA91 can be eliminated together with some capacitors. The antenna will damp the tuned circuit...
  15. duke37

    Can I Use A Motor From a Fan For Electricity

    There are many kinds of motors. Some will generate, others will not. If a motor is to generate, it will need to contain a permanent magnet. This can be discoverd by holding a needle on a thread and see if it is pulled towards the motor. Also, most permanent magnet motors when turned will seem...
  16. duke37

    Help with time delay relay circuit

    I have mended electric fence energisers and they seem to last better if they are in a box with a small ventilation hole in the bottom. I have coated boards with Waxoyl which is intended for car undersealing. It gives a wax coating which can be removed with paraffin or white spirit, the problem...
  17. duke37

    What Gauge Copper Wire Should I Use?

    You cannot use bare wire in a coil since conduction between turns will short out the coil. Enamelled wire (magnet wire) is the way to go. A few turns of thick wire will give a low voltage and a high current, a lot of turns of thin wire will give a high voltage but a low current. The power...
  18. duke37

    AC to DC converter (using envelope detector)

    This is a circuit of a simple diode detector and an amplified version. This could be made into a scaling amplifier by tapping down the resistor to provide the feedback. I am not into the latest amplifiers but you will need one which is fairly agile and, if you only have a single polarity...
  19. duke37

    I (a newb) would like to design a small & simple GPS tracking system for my 2 cats

    I would not know how to do this, however, GPS is a one way system, there is no way of sending requests or data to the satellites. You could perhaps get a transmitter working in the 400MHz region to send the data to a receiver. If the transmitter was activated for a second every minute, the...
  20. duke37

    AC to DC converter (using envelope detector)

    It does not look as if you need anything special. With a voltage input of a volt or so, a simple diode detector will not be adequate but an "amplified diode" will do the job. This will need to feed a capacitor which should have a resistor across it to discharge it when the signal stops. The time...
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