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  1. duke37

    multi direction dc motor

    The 2N3904 is rated at 200mA maximum, perhaps your motor consumes more than this. I do not understand how you use four of these in an H-bridge. Post a diagram of what you have.
  2. duke37

    Microcontroller and home automation control project

    Ther was a thread here 'Automatic chicken coop door opener' here a while ago. You could have a look at that to start.
  3. duke37

    earth fault

    He is in the UK so 230V and 440W. You need to measure the resistance between the heating element and the pot, the big pin on the plug to one of the smaller pins. The resistance should be several megohms so use your meter on the highest range.
  4. duke37

    help needed

    Some combine harvesters detect grain passing over the sieves with a plate which detects the seed hitting it. A diddy microphone attached to the tube should be able to detect the seed where the tube is curved. The signal will need to be filtered to select the seed signal among the noise.
  5. duke37

    Clapp Oscillator

    Efficiency is defined as power-out divided by power-in. Power-in is voltage-in times current-in. Power-out is voltage-out (RMS) squared divided by load resistance. The easy way of finding out if the oscillations are sustained is to look at the output with an oscilloscope or an AC voltmeter...
  6. duke37

    Plz explain me behaviour of Speaker

    In your first picture, the speaker should give out a sound but I have not worked out the cut-off frequency so the output may be greatly attenuated. In your second picture, the speaker input is shorted so it cannot give any sound out even though you say it does.
  7. duke37

    Help understanding simple solar charging circuit

    Having another look at your circuit, the series resistor is much higher specified than necessary. The power in a resistor is V*V/R, i.e. 0.7*0.7/0.5 this comes down to about 1/4 W. A half watt resistor would be fine and a lot smaller and easier to fit than a bulb. duke
  8. duke37

    Help understanding simple solar charging circuit

    A 6V 7W bulb will be vey different to a 240V 7W bulb. In use the maximum voltage across the bulb will be 0.7V so a low voltage resistance measurement may be not far out. The diode is necessary to stop battery discharge when the light is low. I do not know whether a capacitor is necessary on...
  9. duke37

    AC/DC power supply

    The transformer primary will be the two connections that go into the wall. You do not need to dismantle anything to check the primary. If it is a switch mode power supply it will be weigh very little and be open circuit on the primary except for when the meter is first connected which will...
  10. duke37

    Help understanding simple solar charging circuit

    I think that a link is missing. A connection should be made from the junction of the 100R resistor and the 220nF capacitor to the battery negative. When there is more than 0.6V across the 0.5R resistor, the transistor turns on and drops the output voltage so limiting the current to about 1.2A.
  11. duke37

    Geyser 4kw to 1kw draw

    An AC supply has a voltage which varies as a sine wave, going positive and negative. It is possible to delay the connection to the load at some point in the sine wave. For instance if the load is connected at the peak voltage until the voltage crosses zero, the power will be halved. This is the...
  12. duke37

    Geyser 4kw to 1kw draw

    If the generator is AC, then putting the power through a transformer giving out half voltage, the power will be reduced to a quarter. The transformer will be quite a big lump. The power could also be reduced by a phase control circuit but the generator may object to this.
  13. duke37

    Piezo sensors/ tranducers

    The Digikey reference describes piezo buzzers, not pick-ups. The piezo effect is due to a voltage developed across a cystal when it is deformed (pick-up), or a voltage placed across a crystal will deform it (buzzer). Piezo pick-ups have no coils. Why do you want a stereo pick-up? Why...
  14. duke37

    Ancient (school) electric bell

    I thought the capacitor was across the points, then when I saw the photo, it looks as if it may be across the supply. I would try experimenting with 1nF (1000pF) and work up from there. A capacitor from a car ignition system could be tried. You will need a high voltage capacitor not a diddy...
  15. duke37

    Ancient (school) electric bell

    I assume that the metal box on the left is a capacitor. A blue wire semms to go towards the blue inout wire and the brown input wire has an extension under the blue wire presumably to another connection on the capacitor. Capacitor value and voltage rating would be interesting.
  16. duke37

    Piezo sensors/ tranducers

    Weren't ceramic record player pick-ups based on the piezo principle and were stereo?
  17. duke37

    how to charge a 12V, 44Ah car battery with trickle charger ?

    VA is a term used for AC circuits, how does this apply to a battery? If the charger is charging at 1A and the battery is discharged, the battery therefore needs 44Ah, you need to charge for 44 hours minimum. Having a loose lead/acid battery in a car gives me the collywobles. Have you...
  18. duke37

    How to pick a potenciometer or resister?

    Why not do what I suggest? The generator is designed to be not depedent on the resistance of the sense wires so a single resistor in line will not have much effect and will give unpredictable results. Duke
  19. duke37

    Ancient (school) electric bell

    That's better. The capacitor seems to be connected across the input to reduce interference. The coil wire looks to be quite fine so the operating voltage is not likely to be very low. The bell can run on DC and perhaps AC. The voltage necessary needs to be determined experimentally. The...
  20. duke37

    Ancient (school) electric bell

    All I get is a little red cross which does nothing. At the bottom of the message you type in you have the option of 'post quick reply' or 'go advanced'. In 'go advanced' you can click on a paper clip and attach a photo from your computer or elsewhere.
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