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  1. duke37

    clamping circuits.......mechansim

    The output voltage on the first negative half cycle will be attenuated but once the circuit is running, the output is as shown in my little diagram. Duke
  2. duke37

    How to pick a potenciometer or resister?

    You have not said whether you have a resistor across the sense terminals. If not, it is not surprising that you have had little effect. The idea is to divide the sense voltage with the two resistors. With 100R (!) and 1k you drop the voltage by about 10%, so raising the output by about 10% i.e...
  3. duke37

    Help make this Circuit from Schematic

    jacoroko is right. In the diagram, the transistor emitter is the arrow. The base is the vertical line The collector is the third connection. You need to look up the data sheet to see what the 'pin out' is. Be careful that you get the right pin out diagram, the BC184 and BC184L are the...
  4. duke37

    using car relay for wall outlet power

    The relay can probably stand the voltage but it has a very large current capability. 5A should be plenty. Auto relays are quite massive and consume a considerable amount of power in the coil which has to be supplied by the control circuit. Remember that you have to make an earthed box to...
  5. duke37

    clamping circuits.......mechansim

    The AC signal on the input varies around the reference point. The capacitor passes this waveform but it cannot go below 0V because of the diode, therefore the capacitor is charged by the diode current to raise the voltage above the reference level. The capacitor must be large enough to pass...
  6. duke37

    Ancient (school) electric bell

    If the bell has contacts it was probably run on batteries, perhaps as low as 2V. The capacitor is there to reduce the sparking of the contacts. In your reply, Go Advanced and attach the photo directly. This saves everyone time and effort. Duke
  7. duke37

    How to pick a potenciometer or resister?

    12V car batteries these days are charged between 13.8 and 14.4V and last MUCH longer than when they were overcharged with crude controls. I attach a simple voltage reducer to raise the alternator output. 100R is a way of expessing 100 ohms resistance, I and others use it because we are too...
  8. duke37

    delay circuit

    Sketch attached. The time constant is R*C but the time will depend on the voltage at which the fet turns on.
  9. duke37

    delay circuit

    A good method is to use a much higher resistance to give a longer time constant and then a transistor (FET) to switch the relay. Relays with built in transistors are available but are expensive. A few seconds is possible but to go much longer brings capacitor leakage as a significant factor...
  10. duke37

    clamping circuits.......mechansim

    Give me time to get up and open one eye. A capacitor passes AC but blocks DC so if a diode is placed between the output and ground, the waveform will be raised (or lowered) so that one extreme of the waveform is at ground potential. A high value resistor is used to keep the waveform clamped...
  11. duke37

    220 VAC to 24 VDC

    A switching power supply uses a transformer running at high frequency. Without a transformer the power loss would be horrendous. 12V plug-in power supplies are cheap, a couple of these in series would give 24V. Duke
  12. duke37

    How to pick a potenciometer or resister?

    You need to reduce the voltage that the alternator sees on the sense wires. A resistor in series with the wire of 100R and another on the alternator side to the other wire of 1k will reduce the voltage by about 10% so the alternator voltage will increase to compensate. What will overcharging...
  13. duke37

    Ancient (school) electric bell

    Possible but unlikely that it is a telephone bell. The telephone system puts out an AC signal through a capacitor to ring the bell. If it is a DC bell, then there will be a contact to interrupt the current as the bell vibrates. What tripped the supply? I doubt if it could trip the entire...
  14. duke37

    LM337 circuit

    The wall supply has a transformer in it so you are using one already. I note from the picture that the supply has several plugs that can be connected either way round. Make sure that you get the polarity right before connecting to your circuit. The wall supply will be isolated from ground so...
  15. duke37

    small Magnetic motor repair (this shoudl be simple!!)

    The smallest motors have shaded poles and these produce very little torque at rest, check that the bearings are not stiff. Bigger motors have a capacitor to set the phase in one winding, these capacitors can fail. Bigger yet motors have a capacitor which is switched in during the start and...
  16. duke37

    Beginner Circuit question

    If a circuit does not work, then an understanding of what it shoud do is necessary and then an investigation of what it does do may find the problem. I have not used a 'breadboard' but I did nail some valve holders to a plank about 60 years ago to make a radio. Voltage measurements on the...
  17. duke37

    removing 120 hz from ac line

    I presume that you have AC mains at a frequency of 60Hz. This has a voltage peak 120 times/second and fast acting lights will give flashes at this frequency and I do not see how these can be removed. Small flourescent lights rectify the mains, smooth it slightly, and chop it up at high...
  18. duke37

    Adding digital voltage meter to cicuit

    I should have said regulator! I attach a diagram of how it should be connected. You say that it is vital that you have a 9V supply. You may have one of these but many small unregulated supplies vary quite a lot, they are high with a low load. I would not be surprised at 12V unloaded. Check...
  19. duke37

    Adding digital voltage meter to cicuit

    The voltage drop with a resistor will vary with the current taken by the meter which is not good. The best way would be to use a 5V voltage stabiliser, these are very common as many computer circuits run on 5V. 1A voltage stabitiser 7805, this is protected against short circuit and over...
  20. duke37

    Voltage Signal Circuit Zener

    This is unlikely to work since you are dividing down voltage difference with the voltage. You could try seven 33V zeners (BZX79 0.5W) in series to drop most of the voltage without reducing the voltage difference greatly. The details I have seen is that they have a tolerance of 5% so it may be...
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