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  1. duke37

    Radio transmitter, options for reducing harmonic emissions

    I do not see any DC path to provide power to the fet. There are NO harmonics in a sine wave. The fet drain should go to a parallel tuned circuit connected to the positive supply. It should be designed to give a Q of between 10 and 15. Then make a matching circuit to drive the aerial The audio...
  2. duke37

    Where to buy EPROM window stickers?

    Any garden centre will sell sticky copper slug tape.
  3. duke37

    120VAC --> 12V LED chip

    The led's current is the applied voltage divided by the impedance of the capacitor. The resistor is there to limit the high current which could obtained on switch on. The capacitor should be special which can withstand 120V 60Hz continuously. (X type?)
  4. duke37

    Pairing a guitar pedal with new AC/DC adapter

    The pedal's input, not ouput is 9V. Stuffing 19V into this would soon loose the smoke out. Get a 9V DC power supply and make sure it is connected the right way round. You could also get a buck convertor to go from 19V to 9V but this just gives complication for little advantage.
  5. duke37

    Most inexpensive method for detecting if some current is flowing in 120VAC or 240VAC PCB Trace

    A current transformer could be used if the wire can be broken. You will need a little transformer with a large turns ratio and a load resistor to give a voltage output. There will be galvanic isolation. The transformer may cost more than than the Hall effect device.
  6. duke37

    Board repair help

    I do not know what the strips are but I would try to repair the broken connections with wire enhancement. I would also replace the relay in case the excess heating was produced by faulty contacts. Check that the relay load is reasonable.
  7. duke37

    Do common grounds lead to current flow?

    Draw a loop for each supply, You will see that D2 takes its corrent from the Molex and the only current in the ground wire will be the data control current. Likewise for D3. This current will be very small going to the common ground point. Each loop may have a high current but most of it is...
  8. duke37

    Need help building a speaker.

    If the speaker is to work at a decent depth, then the container will need to be made from strong, heavy material. This will need a high power to vibrate it and the water which it is coupled to.
  9. duke37

    Home theater subwoofer power supply fault

    What do you mean by shorted? If it has 240V on input and output, it is not shorted and is working. Mains power is contaminated by high frequency signals. These are generated by switch mode power supplies, motors with brushes and power supplies with rectifiers. The common mode choke may be there...
  10. duke37

    Induction Heater Diy, How To Improve Performance?

    T1 and T2 will have their bases driven to -12V or so. The limit of base/emitter voltage will be 6V or so. To stop the bases being driven too far negative, put a diode in series with the base or emitter.
  11. duke37

    Connecting wires on two sides (connectors)

    An electronic circuit in a vacuum will overheat unless special measures are taken to transfer the heat to the chamber.
  12. duke37

    Generac generator output

    But several clocks all did the same thing so likely to be synchronous clocks.
  13. duke37

    Voltage divider capacitive dimmers

    If you wish to use capacitors, then the only reasonable sort are those with solid dielectric. These are big and expensive and you will need one for each output level. See motor capacitors, 3μF would be typical for motors in the UK.
  14. duke37

    Generac generator output

    I have a meter which will measure voltage, current and power also frequency. This was obtained from a cheap supermarket, about £8. Testing a friend's small generator showed a frequency of 51Hz unloaded and 49Hz fully loaded. Running with a low frequency can give problems with inductive loads...
  15. duke37

    DC motor brush question

    Make sure that the brushes are free to move in their holders. If the brushes do not fit properly, then the commutator will be damaged. If you remove the brushes, then put them back where they came from to maintain the bed-in. The comm should be chocolate coloured and there should be no sign of...
  16. duke37

    Long range rc circuit

    The locations appear to be fixed. A clear line of sight with high gain aerials at each end should do the job.
  17. duke37

    Need help with buzzer in LED automotive turn signal circuit

    There will be a reservoir capacitor which retains some voltage. This could be reduced in value. A bodge could be added to drop the buzzer voltage when the input power is removed.
  18. duke37

    Low voltage cut in/cut out

    Just leave the fans on maximum and use PWM. Have you worked out how many expensive relays and driver circuits you will need and compared with a cheap PWM module?
  19. duke37

    Low voltage cut in/cut out

    Depending on the way of dropping the fan speed by half, it may need four relays with drivers and some logic. If the fans just use resistors to drop the voltage and so the speed, then I would favour putting both fans on full speed and controlling the speed with a pulse width modulator to drop the...
  20. duke37

    I'm trying to rig a bike horn to an alarm clock

    Thanks CDRIVE, it may be advantageous to put a capacitor across R4 to keep Q3 on between input pulses. Try 100nF.
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