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  1. duke37

    Bilateral switch for PWM

    If you put bridge rectifier in the motor lead, then the current can be made to run in one direction. Thus you can use a FET. You will have to have a floating ground.
  2. duke37

    I need a tutorial on MOSFET gate resistor selection

    Inductive load. It is good practice to put a diode across an inductive load to suppress high inductive pulses. Logic level The optimal voltage may be 10V but 5V should be good enough. 12V rail Go ahead and use 12V. Do not under any circumstances use over 20V. Pulsing The gate may...
  3. duke37

    I need a tutorial on MOSFET gate resistor selection

    Case 1 IRF840 The maximum source-gate voltage is +- 20V and the voltage necessary to turn it fully on is more than 6V. So choose a Zener of about 12V. The Zener is not necessary if you are sure that the gate is not overdriven. Case 2 NTE2987 Similar to case1. A driving voltage of 10V would...
  4. duke37

    Wireless remote driveway sentry?

    Traffic is often monitored with a metal detector system at traffic lights and to monitor speed. For temporary monitoring, they clip a sealed rubber tube to the road and use a pressure switch to detect increase in pressure.
  5. duke37

    Capacitors

    I agree with Jackorocko about the capacitor likely to be an elecrolytic but do not agree with the mechanism. Elecrolytic capacitors are complex beasts and have many parameters to specity them correctly. They need the positive terminal to always be more positive than the negative terminal to...
  6. duke37

    Digital Ceremonial Bugle

    If the speaker is sealed into the bugle, the energy will be much more efficiently transferred to the surroundings as you now have a horn loadspeaker. The impedance of the driver will rise and more voltage will be required but the deflection of the diaphram will reduce. My uncle had a cinema...
  7. duke37

    Capacitors

    Capacitors do not have a threshold but like every other component they have a maximum rating. In your application, the capacitor charges up from the solar panel, in other words the voltage has an AC component. When the capacitor is connected to the electromagnet, the capacitor discharges and...
  8. duke37

    How can current speed up?

    You are right that, in general, the maximum current is with the output of the supply shorted. It is also likely to produce maximum smoke. The load does not "draw" current, "takes" would be a better word. Your understanding is correct, the terminology is incorrect.
  9. duke37

    Schematic to reality conversion

    The ground or earth connection does not necessarily have anything to do with ground! It is merely a reference potential that all other parts of the circuit uses. In low voltage circuits it may not be connected to anything, in mains circuits it is normally connected to physical ground for safety...
  10. duke37

    Need help with visible light photo detector circuit

    OK. Measure the resistance of the cell with and without the led lit. It should then be possible to devise a circuit to switch your load.
  11. duke37

    Need help with visible light photo detector circuit

    A green LED gives an output at 565um, you will need a receiver sensitive around this wavelength. Either a transistor (not infra-red) or LDR (liight dependant resistor) should be suitable. Experiment with the chosen device will be necessary to get a matching circuit.
  12. duke37

    Need help with visible light photo detector circuit

    If you can get at the supply to the LED, then a single transistor could probably be used. If you go for a photo detector, you will have problems with ambient light. Photo transistors are small and light, you would want one with maximum sensitivty to the wavelengh of the LED.
  13. duke37

    Safest way to switch 240VAC

    You should look at the regulations concerning this. The supply company do not look kindly on power being supplied from the wrong end. You probably need an approved manual change over switch.
  14. duke37

    TV Licencing

    In the UK the BBC provides several free high quality radio programs (no adverts) and the TV licence goes towards paying for these. A radio licence is not now needed. I listen to Radio 4 quite a bit and only go to Classic FM (commercial) when travelling in a car. I used to know a radio amateur...
  15. duke37

    555 Timer Problem

    Very little current (negligible) goes in or out of the trigger comparator (pin 2) or the threshold comparator (pin 6). Current comes from the positive supply through a resistor to the capacitor and pin 7. When the IC triggers, a transistor connects pin 7 to ground, discharging the capacitor.
  16. duke37

    TV Licencing

    Any fast switching electronic circuit will emit radiation which can be detected with suitable equipment. For the last 60 years or so the TVs have been superhets where an oscillator is used to move the incoming frequency to a common intermediate frequency. The frequency of this oscillator will...
  17. duke37

    high voltage triac circuit

    The generator probably has a high leakage inductance to limit the current and compensate for frequency variations but you are right in that it will introduce extra stress. You say that you could interrupt either the red or white wire to stop the engine. I would not touch the white wire since...
  18. duke37

    high voltage triac circuit

    The Vespa has a switch to stop the engine. The engine can be stopped by paralleling this switch with some device. I suggest a relay connecting the green and white (frame) wires together. Presumably shorting the output of the alternator will not cause problems since the stop switch does this.
  19. duke37

    Whats the error in attached band pass filter?

    You say that the first filter has a turn over frequency of 704Hz but you have two loading resistors effectively in parallel, giving half the load resistance, hence a turn over frequency of 1408Hz.
  20. duke37

    To SCR or not SCR?

    Assuming no losses, the energy in the capacitor will go into the inductor. 0.5 * C * V*V = 0.5 * L * I*I so I = V * sqrt(C/L) Taking 300V, 200uF, E=9J, with L=1.5H, Ipeak=3.5A The current will continue until the capacitor is charged in the reverse direction which is disastrous if it...
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