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  1. duke37

    Transistor how much current is needed to activate them?

    Comment on Harald's circuit. I think that the fet is shown as P channel, I think it should be N channel. A Schottky rectifier (e.g. BAT43) will have a lower voltage drop than the standard 1N4148. A transformer from an early transistor radio set would do the job. Find a repairer or someone...
  2. duke37

    Transistor how much current is needed to activate them?

    Junction transistor A junction transistor needs an input current to operate with a voltage of 0.6V relative to the emitter. The transistor will have a current gain (Hfe) of perhaps 100 so you can get 100 times the input current through the collector. Mosfet A mosfet needs a voltage on its...
  3. duke37

    Nuclear Plant help

    A nuclear reaction in one fuel element will produce neutrons which are slowed down by the water as moderator so that when they enter the next fuel element they are at an optimum speed to set off the next nuclear reaction. The nuclear reactions without the modulator will be less than optimum and...
  4. duke37

    High Q bandpass for 50kHz

    I have 'Electronic Filter Design Handbook' by A.B.Williams. He says that the multiple feedback circuit is suitable for Q<20. He gives an example of a dual amplifier feedback circuit with Q=70. He says the biquad can have Q=200, I do not know why your circuit does not behave, perhaps it is the...
  5. duke37

    Activate tiny RELAY by headphone jack?? (PLEASE HELP)

    I have not looked up the data for the IRF640 but it probably has a threshold voltage of 3 or 4V so will not do any thing with a signal below this. There are mosfets suitable for digital circuits with lower threshold voltages. You could consider an audio transformer to raise the voltage to a...
  6. duke37

    types of metal

    Car gearboxes use hardened steel gears. Old clocks use brass wheels meshing onto steel pinions. The hard steel wears faster than the brass. Car differentials used to use bronze worms onto steel gears. The windmill close to where I live uses wooden gears, I have forgotten the type of wood but...
  7. duke37

    Conversion from [-10,10]V to [0,5]V range

    IC2A This is a common circuit. The input impedance is very high since the IC will take negligible current. The output impedance is very low since the IC drives the output to match the input.
  8. duke37

    Activate tiny RELAY by headphone jack?? (PLEASE HELP)

    You can use a transistor or intgrated circuit to amplify the signal to switch a high power. In order to do this, you will need a power supply which I thought you did not want.
  9. duke37

    Hijacker needs help (LED traffic lights)

    The three spare gates need their inputs connected to something to stop them going bananas, I chose ground. The outputs are left open. The 555 will do the same job as the NAND gate but the NAND gate is a bit simpler.
  10. duke37

    Hijacker needs help (LED traffic lights)

    I do not see how the red leds can show without other leds showing also. There are other traffic light circuits out there with the leds diode connected to the 4017. I attach a diagram of my circuit which was used to train children in the operation of traffic lights and so it needed to provide...
  11. duke37

    Need Help if i can study electronics

    In my experience learning something with no interest in it is very difficult. I would suggest that you get a book on basic electronics and list out the half dozen equations that will be needed in most circuits. You will need to know how to transpose equations and what the multiples and...
  12. duke37

    Help with some components

    You need to drop about 3V at 100mA (0.1A) so will need a 27 or 33 ohm resistor in series with the motor. Ohms law V=I*R , voltage = current * resistance
  13. duke37

    Help with some components

    1. The diode should be capable of passing the motor current but it only does this during the actual turn off. The common diodes are 1N4001 to 1N4007, these are rated at 1A but can pass more than this for a split second. 2. The 1M potentiometer looks right. 3. Any small resistor of the right...
  14. duke37

    Activate tiny RELAY by headphone jack?? (PLEASE HELP)

    This looks impossible without an amplifier and power supply. What is very small? Gas central heating boilers use a thermocouple to drive a relay but this is DC. If you rectify the signal to get DC you will lose voltage in the diodes. If you need the relay to hold for a time, you will need...
  15. duke37

    buss fuses

    What is the voltage of your battery? Using a fuse above its voltage rating does not guarantee that the fuse will open properly or the fuse may explode.
  16. duke37

    laser alarm problem

    Engineering King I am not happy with this circuit, I think it needs quite a bit of correction. I have not analysed the circuit but have pointed out obvious errors. Are you asking how to construct the circuit? For a simple circuit such as this I would use strip board (Vero board) and work...
  17. duke37

    help with volume control circuit

    Looking at the duncanamps site, it appears that the tone control should be fed with a low impedance. You have this. The circuit should feed into a high impedance, there are components for 1M or 2.2M. You could try a 1M log pot but will need an amplifier with a high input impedance, do you have...
  18. duke37

    help with volume control circuit

    Never heard of a ipaq. A 10k log potentiometer would be OK to put across tha output of your device. The output should be taken from the slider and ground. If you get the pot the wrong way round, the volume will change very fast at one end of the control. I Googled Baxandall and got a...
  19. duke37

    27MHz colpitts oscillator qestion

    It must be 50 years since I played with 27MHz equipment so I cannot be definitive but I think I used a 3 to 30pF trimmer for C3 and about 10 turns of 0.25 inch diameter for the inductance. What would your 50nH inductance consist of? C1 is there to hold the base at a constant voltage. The...
  20. duke37

    AC snub?

    DC relays can stick due to retained magnetism and a little brass screw is sometimes fitted to stop the armature closing fully. This could be adjusted.
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