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  1. duke37

    help needed for engineering college project

    Should it be maximum resistance? Does the project include power losses?
  2. duke37

    Need help determining components for a circuit.

    The common small silicon diodes are 1N914 and similar 1N4148. Yellow is 4, look up the other colours.
  3. duke37

    how to achieve desired delay time in cmos inverter

    I had a look at the delay of a 4001 chip, this was given as 60ns. I do not see how CMOS can get down to 215ps. The speed of light is 300E6 m/s so you could use a short delay line and subtract one delay from another.
  4. duke37

    simple radio building

    Transistors will pass curent in eiher direction depending on the circuit but you need to know what you are doing if you run them in unusual modes. Why would you want to do this? The circuit is just an amplified crystal set and will have very poor sensitivity and selectivity. Depending on...
  5. duke37

    Infrared laser for communication

    RadCom, the journal of the RSGB has had some articles on long distance communication using leds. The latest uses a lens from Poundland to focus the beam. Fresnel lenses as used in car rear windows have also been used. You must get a lens which has low absorption at the wavelength you are using.
  6. duke37

    Help with a simple relay switch oo gauge train modelling connecting two circuits together

    A 24V relay will not work reliably on your much lower voltage. Rather than me reading the thread from the beginning please define 1. The voltage source to drive the relay. 2. The load voltage and current £. The contact configuration.
  7. duke37

    Driving SCRs for coil gun and EMF protection

    Surely, a conductive tube like brass will absorb the energy by eddy currents so the gun will have little push.
  8. duke37

    Are these capacitors neccessary?

    I would not worry about the alternator but there are other things around like the starter which can cause voltage spikes, the supply in a car can be very dirty. I have recently repaired a board out of a combine harvester. This was fitted with a protection diode which limited the voltage and if...
  9. duke37

    12v 4A power supply

    It depends on whether the output is AC or DC and what stability is required. A simple solution for a 'dirty' supply is to use a simple old style battery charger with a big capacitor on the output. You will get DC at more than 12V. The difficuty in building your own supply is boxing it up to be...
  10. duke37

    Are these capacitors neccessary?

    The capacitors are there to stabilise the power supply when the IC produces pulses. Leaving them out, may work but it may also upset other components connected to the same power supply. The values are not critical so you may have something similar that would do.
  11. duke37

    Driving SCRs for coil gun and EMF protection

    Rather than trying to drive at a specific voltage, you should drive at defined current (100mA). From 5V, you will have 5-1.25V available so use a 33R resistor. The SCR will turn off when the holding current drops below the threshold. This may occur when the coil resonates. The trigger must be...
  12. duke37

    24 volt ac relay chatter in parallel to doorbell

    Does the power supply hold up at 24V with both things in parallel? You cannot put a diode across a AC relay. The relay can be made more sensitive if fed with DC. You could try a bridge rectifier but take note of the power dissipation.
  13. duke37

    Explain the principle of operation of a synchronous generator with the aid of calculations.

    Quite a good exposition. The laminations are not steel, this term is normally used for an iron/carbon alloy or stainless steel. The laminations are iron/silicon (4%) with minimum carbon. The silicon iron has low magnetic loss and a high electrical resistance to minimise eddy currents. The DC...
  14. duke37

    Help please

    All the hot air guns I have seen have the power requirement on a label. You will need 100A or more from 12V. A 50Ah battery might last 15 minutes if it can last this long wihout overheating.
  15. duke37

    Transformer Voltage Amplifier

    You will need to give more details on the 3.7V supply and the motor requirements. You will not be able to run a 12V motor full speed from a 12V variable power supply because of losses in the controller.
  16. duke37

    Do a variable AC, high-amp power supply exists?

    You could modify a HF transmitter. You will need a BIG cable to feed the power into your house.
  17. duke37

    Help with a simple relay switch oo gauge train modelling connecting two circuits together

    The built-in diode will do the job but the polarity must be right. Nothing should get hot, if it does, the polarity is probably wrong. Check the resistance of the coil with a meter using both polarities. There should be a measurement of coil resistance (700 ohm) in one direction and much less in...
  18. duke37

    Help with a simple relay switch oo gauge train modelling connecting two circuits together

    That relay should work at your source voltage. I do not know what the decoder will stand but relay coils can produce high voltages which can be damaging. To protect against these, a diode should be connected across the coil. Any small power diode will do, the common series is 1N4001 to 1N4007...
  19. duke37

    Help with a simple relay switch oo gauge train modelling connecting two circuits together

    You could add a resistor in series with the relay coil if there is a danger of overheating the coil. The coil takes 16.6mA so you can calculate the necessary resistance from the voltage drop you require to get down to 12v I would not use a relay but a MOSFET, Maplin shows an IRF540 in an old...
  20. duke37

    ac voltage regulator

    The second circuit will work to clip the peaks so will help to extend the life of bulbs. The trouble may be to find zener diodes which can handle the power. I have not looked up what is available. If you use a bridge rectifier to get a unidirectional supply, then a single zener can be used. To...
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