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  1. duke37

    Coil can be replaced by Inductor for a bridge rectifier?

    You should define what you mean by a coil and an inductor. You will need to determine the voltage and current necessary to operate the valve. SMT components are often weaker than the bridge block rectifiers. I would prefer the rectifier to be separate from the coil. Vibration and temperature...
  2. duke37

    Soil moisture sensor

    Gold plated wire has been used for electronic organ contacts and a meter of this should be affordible. It is very small diameter though so the resistance to soil may be too high. Platinum and platinum/rhodium wire should also do but you may need to sell your tiara to buy it.:)
  3. duke37

    Decoupling capacitor

    The capacitors which have been specified are colossal. Do you mean μf rather than mF?
  4. duke37

    Bi-directional Motor with speed control circuit

    Relays will be bigger and possibly more expensive. They may have contact problems and may need fettling after 100,000 operations. They will be more robust if subjected to high voltage pulses but the 555 will likely fail first.
  5. duke37

    Bi-directional Motor with speed control circuit

    Use a single two plole changeover relay to swap the motor leads over. When the relay is energised, the motor will run one way, when unenergised it will run the other way. This is an alternative to the H Bridge. Using two relays means that you need circuitry to ensure that the motor is not asked...
  6. duke37

    Variac VA

    The current limit will be more to do with the brush connection rather than the wire diameter. In this respect, current limit is a better measure than VA. VA will depend on set output voltage.
  7. duke37

    Light switch

    You might have a junction box with bad connections. I believe that the US uses screwed on ceramic connectors. These were made obsolete in the UK before WW2. You can make a little RF generator to input a signal where there is no power and trace back from there with a portable radio.
  8. duke37

    Help with current limiting on etrike

    You cannot do this, the current will depend on the voltage. You can control voltage and maximum current but not at the same time.
  9. duke37

    Component recognition

    Is that a helical wire? If so, it is could be a very low value resistor.
  10. duke37

    Fishing trolley will not STOP

    The soldering looks a bit blobby on the fets. If the fault is intermittent, then the fets are OK. If the gate of a fet is not connected to a defined voltage, then the fet can do its own thing and turn on and off with a whim.
  11. duke37

    Morphy Richards electric blanket controller pcb fault BEPCB020

    The local fire brigade used to check electrical blankets, I do not think any passed.:) Look to see if there is a connection in the blanket, Assume the blue wire is common and see if there is a connection to the other wires. I think there should be a connection between all wires. The soldering...
  12. duke37

    NPN transistor still working? Strange ..

    My thought is that a zener diode is designed to dissipate heat but the transistor base is not so that a variation in temperature could cause a variation in breakdown voltage. A dynamic measurement of the voltage across the transistor would be interesting. The emitter/base junction seems to be...
  13. duke37

    NPN transistor still working? Strange ..

    The transistor is upside down. The emitter is normally connected to the negative supply and the collector to the positive. Transistors such as the 2N2222 has a limit of about 6V negative, emitter to base, so the transistor will pass current when this is exeeded and discharge the capacitor into...
  14. duke37

    FM transmitter power

    You will need to do a redesign, changing resistors, capacitors and inductors. Also you may need more gain by adding another amplifier. It will all depend on the frequency which is not specified.
  15. duke37

    Rapidly change electro magnet polarity.

    A two pole changeover relay wil give the action you want but may not work at a few hundred times a second and if it does work is likely to wear out quickly. The magnets will have an inductance, possibly large. Perhaps laminated pole pieces would be best. An H bridge is the alternative, it will...
  16. duke37

    Popping sound when switching microphone with relay

    So, how would it be connected? If it is connected to action the zener voltage during switch off, then it will short the relay coil when the relay is energised. Adding a diode in series will stop the short and limit the voltage on the coil during switch off. An alternative connection is to...
  17. duke37

    Popping sound when switching microphone with relay

    Here the relay is controlled with a switch which will arc when turned off thus giving a click. As davenn says, a diode will suppress this arc. A capacitor across the switch may also do this. It is cheap enough to try both diode and capacitor. A zener diode cannot be connected across the relay...
  18. duke37

    Popping sound when switching microphone with relay

    A capacitor across the switch may help also, I would try a 0.1μF.
  19. duke37

    Popping sound when switching microphone with relay

    A zener diode across the coil seems to unnecessary, they are used to switch the relay off rapidly. Are you worried about a few milliseconds? An ordinary diode will limit the pulse voltage to very little. Almost any diode will do, the common range is 1N400x and 1N4007 will do for many other...
  20. duke37

    Using a PIR to turn a light OFF

    There may be a changeover relay in the PIR or you may be able to fit one.
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