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  1. duke37

    Multiple Sliding Doors - Hobby

    I think the cmos 4192 (40192) up/down counter should be able to do the job. I do not have the time to consider further. A 4017 will count 0 to 10 to open the doors with perhaps another to shut them. A microprocessor will do what you want with simpler circuitry but it is not in my area of...
  2. duke37

    Can someone explain me how a BJT works?

    You brought in the term power, presumably this was power delivered to the output or in other words the load. This may be a resistor to generate a voltage or a motor or a speaker. A heat sink is a component to take away heat from a hot component and spread it around. The most common is a block...
  3. duke37

    Can someone explain me how a BJT works?

    A BJT needs base current to raise the base voltage a little. It can be used as an amplifier or turn it on hard enough to act like a switch. Even so, the voltage drop can be up to 1V so may need a heat sink. The power will depend on the load. The common n-channel FET needs voltage at the gate...
  4. duke37

    need help with a relay

    Welcome to the forum. Please tell us what your knowledge is. You could use a CMOS 4017 decade Johnson counter. It will need input and output circuitry to debounce the input and driver circuitry depending on what you wish to do.
  5. duke37

    Buck operation using IR2117 gate driver

    How can a buck convertor produce 40V from 20V?
  6. duke37

    2 transistor oscillator

    This is a multivibrator, collector to base, collector to base. With two similar transistors, one will be on when the other is off. In this case, Q1 is npn and Q2 is pnp and both transistors go on and off together. Assuming the oscillator is running, when Q2 is on, the collector is pulled high...
  7. duke37

    Appropriate Oscillator

    1. A fet needs negligible drive current but does need a fair amount of voltage. The fet when turned on has a very low resistance so will dissipate very little heat. A npn/pnp transistor needs considerable current drive and will drop about a volt so may need a heat sink. 2. A cmos 4060...
  8. duke37

    Radio waves question.

    But it is not the frequencies that you multiply, it is the instantaneous voltages of the two inputs to generate a new waveform. The traditional high level anode modulation varies the output voltage due to the change in HT voltage. Interestingly,a similar process occurs during demodulation...
  9. duke37

    Appropriate Oscillator

    To get accurate frequency, you need a crystal oscillator followed by a divider. To get more consistency than a 555 you could use a ceramic resonator (dirt cheap). A 455kHz resonator divided by 8 may be near enough. There should be no problem getting a more powerful square wave output using a...
  10. duke37

    Radio waves question.

    If I remember right, sin A * sin B = sin (A+B) + sin (A -B) In other words this form of mixing is done by multiplying. Audio mixing in a mixer is done by adding.
  11. duke37

    Radio waves question.

    To make things a little more complicated, as @dorke said, the carrier and audio are multiplied together. The result is the carrier plus an upper sideband and a lower sideband. The sound information is in the sidebands and it is possible use only one of these and dispense with the carrier, saving...
  12. duke37

    Obscure high power electronic device,what is it?

    The scanning electron microscope I used to play with was energised with EL34 valves so this one is new.:) The circuit is almost certainly a voltage multiplier so the red blocks could be capacitors or rectifiers. If they are rectifiers, they will have several diodes in series and will need a...
  13. duke37

    Radio waves question.

    To generate a high frequency wave was very difficult and various designs of alternator were developed. To get a frequency of say 200kHz, the alternator had to have many poles and run as if the devil was after it. To send information, they used Morse code initially by switching the alternator on...
  14. duke37

    Need advise - Screwed up on my PCB - Need replacement part

    You need R1 or R8, not both. That would make things a bit simpler. If you have populated only one board, you could turn the leds round. Cut the track from Vcc to the leds and connect them to GND.
  15. duke37

    Would like some advice about my motor speed control circuit.

    Gate resistor. I have never used a gate resistor and had no trouble. I understand that the purpose is the same as the reason for a grid stopper. The fet can act as an oscillator with the gate capacitance as part of the oscillating circuit and the resistor will damp this. There will be no current...
  16. duke37

    DC Motor drive

    An AC dimmer is triggered with a diac. Some are more symmetrical than others. You do not need to smooth any output to drive a motor.
  17. duke37

    Would like some advice about my motor speed control circuit.

    A cmos 555 will use little power and will be able to drive a fet which needs negligible gate current.
  18. duke37

    DC Motor drive

    I am not going to learn a lot of programming. I last programmed a 3502 in an Apple ][ to drive a 250kW DC motor about 50 years ago, not starting again now. I did learn that correct spelling was mandatory. A dimmer needs to be symmetrical if driving a transformer. My previous trial of a SCR...
  19. duke37

    Would like some advice about my motor speed control circuit.

    A npn transistor will need up to 1V to pass the current required, this means that several watts will be dissipated. A mosfet can be turned on to give a very low resistance so that the dissipation is very low and I doubt if you will need a heat sink. You have 12V which is plenty to turn the fet...
  20. duke37

    Single led vumeter using LM311 comparator at the output amplifier?

    Why won't it work? If the LM311 is set to give a low output when there is no signal, the fet will be off and there will be no light. If there is sufficient signal, then the LM311 output will be high for part of the time and the led will be on for part of the time. In other words it is a peak...
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