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  1. duke37

    Amplifier antenna question

    Plugging anything into a guitar amplifier will only give audio frequencies. If the amplifier is sufficiently sensitive then you will hear mains hum and hash from switch mode power supplies. The difficulty is keeping this rubbish out of sensitive equirment. Radio and television programs are...
  2. duke37

    How to change 5DCV into +/- 5DCV

    There are chips which will produce -5V from a +5V supply. I have never used one. It all depends on what power you want.
  3. duke37

    do i need resistor for 50-70 leds?

    With 9V you may be able to get three leds and a resistor in a string. 20 strings = 60 leds. 20 strings at 20mA = 0.4A. How long will the battery last?
  4. duke37

    Micro water pump

    The pump takes about 1/4W and if my sums are correct, then a 12V 7A.hr battery will store sufficient energy to run continuously. You will need a buck convertor to drop the voltage but at this low voltage is unlikely to be very efficient. Chris's idea seems the easiest way to go. A magnet...
  5. duke37

    Backup Internet Access through Secondary Router

    I am not sure what you have, a centre tapped winding and two diodes will give full wave rectification. If you use half the winding and a bridge recitfier you will also get full wave rectification but a lower voltage since there will be an extra diode voltage drop. There will be considerable...
  6. duke37

    multiple displays

    I am not an expert on these, however this will not stop me! If you use more than one meter on the current source, the meters will need to be connected in series. they may not like not being able to find their own ground. The input impedance will be determind by a resistor to generate a...
  7. duke37

    IC Voltage Regulator Question

    Hve you checked that there is no thermal aspect? If the gauge operates rapidly, there is not. If the gauge creeps to its final reading, then there is. Thermal meters were used because the slopping of fuel in the tank made reading the level on the move very difficult. You should measure the...
  8. duke37

    Backup Internet Access through Secondary Router

    You have not said whether you have added a diode to convert to full wave rectification. You should measure the voltage on the input to the stabiliser, if this drops too low between charging pulses, then the output will be low.
  9. duke37

    Relay acvitation on multiple Temperatures of an Object??

    I would think that epoxy resin (Araldite) would fix the thermistor to the pipe. There may be problems with differential thermal expansion. A wooden block held with a screw clamp would also do. There is a type of tape, usually yellow, (I forget the name) which is used to hold the windings...
  10. duke37

    IC Voltage Regulator Question

    The NTE962 seems to have a current limitof about 1A, this may not be enough for the gauge you have and the voltage drops as a result. There were two types of fuel gauge, one was a moving coil gauge which responded very quickly, this needed a smooth supply. The other type was a thermal gauge...
  11. duke37

    Wanted: spdt short lever toggle

    These look to be a common type of switch although they are often double pole, you do not have to use the other pole. In the UK you can try:- RS, Maplin (there are many local shops), Farnell, Cricklewood, Bowood, Potts (Derby, not far from the bus or train station).
  12. duke37

    Help with voltage doubler

    This is not a voltage doubler, it is a method of shifting the average voltage using the diode as has been said. To get a voltage doubler, you need a diode on the output, feeding into a reservoir capacitor. You can use more than one stage - see Cockroft-Walton multiplier - to generate vast...
  13. duke37

    AC fan polarity problem

    AC means alternating current. In other words, the polarity is constantly reversing. Therefore it does not matter if you reverse the wires. If you are playing with 240V and do not know what you are doing, get someone to help who can ensure that you are safe.
  14. duke37

    Backup Internet Access through Secondary Router

    Why use a half wave rectifier, put another diode in and make it full wave. How fussy is the router. The battery should be sufficient to control the voltage to 14V on charge and 12V on discharge. Measure the input and output voltages of the regulator and the battery when the mains is on and...
  15. duke37

    DC Fan Transistor Switch and Amplifier

    You could put a variable resistance between the power supply and the fan but this would need a big resistor and would dissipate a lot of heat. If the current into the base of the transistor is controlled, the collector current will be the base current times the transistor gain, a guess of this...
  16. duke37

    Backup Internet Access through Secondary Router

    Maybe the regulator voltage is a bit low. The battery should have 14V on it when charging. At a fairly high current the diode will drop about a volt, so the regulator will need to supply about about 15V. I think the regulator output will be a little low Am I wrong when I calculate 11.6V?
  17. duke37

    DC Fan Transistor Switch and Amplifier

    Q1 just dumps current and wastes power.Turn it up and you could blow it up. Get rid of this and use the pot to control the current to Q2.
  18. duke37

    Radio button lights up a bulb in another room

    :)*steve* Great minds - - - - Duke:)
  19. duke37

    Radio button lights up a bulb in another room

    My thought would be to use a wireless doorbell with a latch circuit (relay) attached.
  20. duke37

    Not Sure How to Hook Up Power Supply to Motor

    This is a 220V 60Hz AC motor, it will not work on DC. The connections are screw teminals in the plastic connector on the side. If you are a novice, I would suggest that you get someone who knows how to wire it up and make a safe container for it. Mains voltages are not for novices.
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