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  1. duke37

    Recharging a car battery

    It depends on the motor. If it is a permanent magnet motor, then it will need to be run at half rated speed and have a diode in series to stop reverse current. If it has a wound field, then the field current can be varied to compensate fror speed. A car dynamo or car alternator do this...
  2. duke37

    open Collector comparator LM339N

    It would be easier to understand with one ground rail. Two of your ground connections short out D3.
  3. duke37

    Transistor Mosfet pairs to drive LED cube layers

    There should be a resistor in series with each led to control the current. The higher the voltage, the more power will be dissipated. In your case, the TLC5940 will presumably do this job but I have not looked up the data. The speed at which the fets will switch will depend on the strength of...
  4. duke37

    Transistor Mosfet pairs to drive LED cube layers

    Another possible problem. The IRF5210 can have a source/gate threshold voltage up to 4V. With a 5V source and 0.5V drop across the transistor you could have only 0.5V to turn on the fet. The fets are powerful and this may be enough but will need checking. Normally, 10 or 12V would be used to...
  5. duke37

    Transistor Mosfet pairs to drive LED cube layers

    A pull up resistor is to pull up the output when no current is pulled through it. The base resistor is to limit the base current into the transistor. The transistor will need about 0.6V to turn it on and with 3.3V source, there is 2.7V to drop. A resistor of 2k2 will give a current of about...
  6. duke37

    Are these MOSFET's the same?

    You could use a lamp limiter to restrict the current supplied to the amp thus being able to test without destroying any more transistors. If the amp works on low volume and no components get hot, then the limiter can be removed.
  7. duke37

    resistor question on 'aircasting' project

    I would think that any 27 ohm resistor would work in this circuit. The resistors run in a low powered circuit and the power is likely to be low. I have not calculated the power. A 27 ohm resistor will have the colours:- Red 2 Violet 7 Black 0 (number of zeros) A quarter or half watt...
  8. duke37

    Pickup Winder Build

    What is the purpose of the speed control? Could you just put a resistor from the power supply to the motor to give a reasonable speed. I am at present building a speed controlled drive (car radiator fan motor) to power an AVO coil winder. You may not wind as fast as you would do with an...
  9. duke37

    Check transistor

    The transistor may be npn or pnp and the polarity will differ. Small transistors can be EBC or BCE. Big transistors usually have the collector in the centre and it is often connected to a tab for cooling. You can use a meter to measure resistance between the leads. The base will be the lead...
  10. duke37

    Skeleton Potentiometer

    I have used Maplin switch cleaner, others recommend Servisol. The skeleton pot is likely used for calibration and could be replaced by two fixed resistors of the correct value. I presume that if the readings are unreliable then this is due to the moving potentiometer controlled by the fuel...
  11. duke37

    Skeleton Potentiometer

    If it sometimes works, try a squirt with some switch cleaner.
  12. duke37

    Voltage Regulator - L7812CV

    Where are you getting the power from? You will need 15V on the input to get 12V on the output. The 3V difference is known as the drop out. If a regulator is working properly, there will be negligible ripple on the output, the capacitors are there to ensure stability. Why not look up the data...
  13. duke37

    Amplifier power supply capacitor removal advice needed!

    Could the problem be another faulty capacitor?
  14. duke37

    Voltage Regulation / Selection

    I see no regulator but there is a capacitor connected to a winding (SW), this may have something to do with regulation. VSsw switches between the two output voltages, this uses the output winding and rectifier connected in a different way
  15. duke37

    need help with my project

    I would think that voice recognition would be difficult. Have you thought of a tone detector, possibly using a sheepdog whistle as the transmitter. If you have perfect pitch you would not need the whistle, you could do it yourself.
  16. duke37

    Basic Circuit.

    The LM10 has an iternal voltage reference and does not use an external cell as I thought. Pins 1 an 8 are connected together so you will not need to cut the track between these. For a simple circuit such as this, I suggest you get some 0.1inch squared paper, a soft pencil and a rubber and...
  17. duke37

    help with a small project - precise 1rpm motor & circut

    Strip board, origionally made by Vero, is SRBP board which comes in various designs. The most common has holes in a square matrix, spaced at 0.1 in (2.54mm). One side of the board has copper strips running in one direction. Standard components can be placed with their leads through the holes and...
  18. duke37

    help with a small project - precise 1rpm motor & circut

    My thought is that you do not need 1rpm exactly since you can vary the motor speed with R1 to suit. The speed could vary with temperature and motor friction. A better but much more complicated method would be to use a stepper motor controlled with a micro as timer. You can get components...
  19. duke37

    Basic Circuit.

    Ey Oop, You have two op amps in one package. The top opamp works as a comparator and switches on the load when the input is geater than15mV. The lower op amp is a voltage follower, it has a 200mV cell as its input and gives out 200mV. The input current of the amp is very low so the small...
  20. duke37

    Help Needed: Building 18V Power Supply for Power Tools

    The alternative to removing turns from the transformer is add turns but connect the winding in opposition. This means that you will not need to damage the transformer in any way. You will need to determine the number of turns/volt which can be done with some thin wire.
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