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  1. duke37

    ? on Resistor placement w/ LEDs

    If you have several leds, off the board, then it will be neater to connect all the leds to the supply and put all the resistors on the board. Just a matter of convenience.
  2. duke37

    advice on repairing a linksys router

    I have repaired electric fence energisers which get clobbered by lightning because they are connected to a long wire aerial. Almost anything can be damaged. Is is obvious that lightning is involved if components are blown apart or the PCB has been stripped of its tracks. Sometimes there is no...
  3. duke37

    My Little Pony fan thread

    Neigh
  4. duke37

    Question: Simple FM reciever????

    I have not seen this circuit either. It looks to me to be an oscillator, running at the FM frequency which is modulated by the incoming signal. Super regenerative receivers are used in car locks. This may be one of those.
  5. duke37

    different current ratings

    The order must be mains, Variac, power supply, water pump. Presumably the power supply is a simple one without voltage regulation and the motor is run on DC.
  6. duke37

    Trouble with diffrential amplifier output

    Here is the basic circuit for a differential amplifier. It has a input resistance of 10k so will not load the bridge to a significant extent. I have set the gain to 10, you could add another amp to get more gain. You will either need a + and - supply or provide a false earth as *Steve* says...
  7. duke37

    Trouble with diffrential amplifier output

    I still do not understand the circuit! One 470k resistor goes to an input so there is little current or voltage drop across it. It could be replaced by a wire. The other 470k goes between the outputs of two op-amps so just provides a load. This could be eliminated. When this is done, you...
  8. duke37

    Schmitt Oscillator

    Schmitt Oscillator I have managed to repair a Copel electric fencer even though the makers would not supply me with a diagram or information on the integrated circuit. I deduced that this is a 40106 hex Schmitt inverter. I have used previously a simple oscillator as in A in the diagram...
  9. duke37

    LED Current Calculation

    You now have a much more reasonable supply voltage. Get rid of the zener, it only consumes power for no reason. If the led voltage is 3.5 ( somewhere in the middle of the range) you need to drop 5.5V. A 270 ohm resistor would give about 20mA. In your circuit, with a 3.3V zener (+/- 5%?)...
  10. duke37

    LED Current Calculation

    You need to define the current through the led not the voltage across it. A led acts as a poor Zener diode so why add another? Decide on a current through the led, say 20mA. Subtract 3.5 from the power supply voltage and calculate the resistor, R=V/I
  11. duke37

    Base Current req to switch on Transistor

    The data sheet of the TIP111 says 2W maximum at 25 degC ambient. I would put a heat sink of about 30*40mm and see how you go. If it is too hot to hold, it is too hot. Small finned heat sinks are often used on TO220 packages.
  12. duke37

    Limit to current?

    Or the load.
  13. duke37

    Problems building first circuit - capacitor ESR meter

    The UF4001 is not a Schottky rectifier, it is a standard fast rectifier. A Schottky would have a lower turn on voltage.
  14. duke37

    What Mosfect acts at Unsmooth DC Voltages

    You have still not said what the fets are doing. As Bob said, 600V fet would be better. Computer power supplies run with a ripple on the supply and the fet control circuit adjusts at high frequency to reduce output ripple. I do not know what the choke would be like, possibly 100*100*100mm...
  15. duke37

    What Mosfect acts at Unsmooth DC Voltages

    1. Do you mean that the circuit is connected directly to the mains without a transformer? 2. Two 200V capacitors in series will not be safe at 400V. The voltage may not be divided equally even with balancing resistors. Why not use 500V capacitors which are available. 3.To smooth 2A a...
  16. duke37

    How UC3845 Control Pin work?

    Both of the circuits operate in the same way. A capacitor is charged up to a high voltage, about +300V. When a positive pulse goes to the gate of the scr, the scr fires and pulls the capacitor down to earth. This gives a 300V negative pulse at the primary of the ignition coil which will be...
  17. duke37

    Trouble with diffrential amplifier output

    I do not follow what the circuit is intended to do. The first op-amp is doubling the voltage of the junction of the left two resistors it should output 2.3V. This is then compared to the output of the pot which presumably is about 2.3/2V The normal instrumentation amp is to use the first...
  18. duke37

    Base Current req to switch on Transistor

    The TIP111 is a Darlington device, it contains two transistors, one driving the other. The gain at 1A collector current is 1000 so 1mA base current should be enough. 2mA would be good. At 1A collector current there will be a voltage drop across the TIP 111 of 2.5V so there will be 2.5W of...
  19. duke37

    video over cat5 without baluns

    Looking up some data, translating from AWG to SWG and viewing my old book, you could have 0.07 ohm/yard. You can calculate the voltage drop if you know the current, remember that the length of the wire is twice that of the cable.
  20. duke37

    Crafty prison inventions

    Tattoo. That looks like a small motor with a crank to push the needle in and out. Kettle. The heating element in the kettle is made of thin resistance wire which is placed inside the large tube. I know not how it is fitted or how a prisoner could get it out without a hack saw.
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