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  1. duke37

    rear wheel curb lights

    Is it legal? To get a delayed turn off, you can charge a capacitor through a diode. The capacitor should have a resistor across it to disharge it after a time when there is no signal. This voltage could be connected to the gate of a fet which switches the extra lights.
  2. duke37

    Multiplying Resistance

    I have done an analysis of your big caps circuit. It mostly attenuates anything in the audio range.
  3. duke37

    Multiplying Resistance

    All capacitors should be the same value. The ones you used are very large. All three at 100nF would be a good try. Using an op amp would hardly be likely to change the response greatly.
  4. duke37

    Designing a sensor.....

    I have calculated the resistance for B values 3500,4000,4500. I could not upload an XLS file so printed the results and scanned them. The resistances vary very rapidly at low temperatures but little at high temperatures. You may be better off using a thermocouple which will be almost linear.
  5. duke37

    Multiplying Resistance

    I have done a simulation in 5spice using a 2N2222. The response is not ideal and deviates a bit when the resistor is high. There is also a strange response in the high audio frequency range. The top diagram shows the response with resistors from 100k on the left to 10k on the right. You can...
  6. duke37

    Multiplying Resistance

    The circiut you show is the same as the one I showed. Mine was a Butterworth which needed one capacitor twice the other and the two resistors the same. You do not say what frequency you want for the turnover. If you divide the capacitor values by 10 then the turnover frequency will go up by 10...
  7. duke37

    Multiplying Resistance

    I have had a look at 'Electronic Filter Design' by Arther B. Williams A simple low pass filter is shown in the top circuit running at 1rad/sec turn over frequency. For a Butterworth filter, C!=1.414; C2=0.7071 The components have to be scaled to convenient values. Taking the frequency...
  8. duke37

    how to connect light indicator

    You should not remove the resistor and if the bulb is designed for the voltage that you have the value should be OK. If you have bought a bulb for 110V, then the resistor should be at least doubled. If the bulb lights when connected directly to the mains, it is working. If it does not light...
  9. duke37

    Designing a sensor.....

    You have not said what your temperature range is or the circuit which needs to be driven. I have not looked into the specification of thermistors but I thought they had quite a wide tolerance. As to the B factor, I would chose a device with a common value rather than an exotic one.
  10. duke37

    Multiplying Resistance

    The 10M resistor is to provide negative DC feedback to set the op amp in the center of the supply. You could try a 1M if you have one but this would reduce the Q of the resonance. Some simulation would be advantageous.
  11. duke37

    Questions about a simple variable power supply

    A mosfet is controlled by the voltage at the gate, the current is essentialy zero if the voltage does not change. If the voltage changes, it is necessary to charge and discharge the input capacitance. A bjt is essentialy controlled by current into the base so should be connected to a low...
  12. duke37

    multisim convergence assistant

    I do not know anything about Multisim. C2 delays the feedback and could put the circuit into oscillation. Try removing it or putting it across R2
  13. duke37

    April Fools "Nuclear Reactor" - Remotely Possible?

    When a radioactive element decays, it produces heat and radiation. This is used in spacecraft. There is no reaction, it is an open ended system. Raven's rocks warm up very slightly. In a reactor, the radiation is used to split other atoms, the output is then much greater but it needs to be...
  14. duke37

    Questions about a simple variable power supply

    1. The 12V zener is to limit the gate/source voltage to +12V and -0.7V 2. The fet will take very little base current so the voltage across R1 will be close to zero. If a bjt is used, then there will be a base current and a voltage drop across R1. You may need a Darlington to work properly. 3...
  15. duke37

    how to connect light indicator

    Neon indicators usually go black rather than burn out. The small neon bulbs need a resistor in series, 270k or so. The higher the resistance, the less light but the longer they will last. Some neon bulbs come with a resistor built in, these will be labelled 250V. One should be connected...
  16. duke37

    Low amps cause my amplifier to smoke?

    You do not give details of the amp however, at low output powers the current drawn should be very low and the bulb would not light or just glow. Consider a drum, to get sound out you have to give it a thump with a stick to put energy in. An amplfier has to provide an electrical thump to the...
  17. duke37

    Low amps cause my amplifier to smoke?

    You could connct it to a 12V battery in series with a headlight bulb. If the quiescent current is low, the lamp will not be bright. If the lamp is bright, measure the voltage across the radio. If it is very low then there is a short inside. Check for any hot components.
  18. duke37

    Circuit design help

    If you put a flap over the bin, coupled to a chageover microswitch, then you can connect each output to a led. The leds will change from green to red and then back to green when the flap returns ti its start position. When the bin is full, the lid will be jammed and the led will stay at red...
  19. duke37

    Motorcycle Flasher Issue

    It may be interference as you surmise but it may also be excess voltage. Motor cycle voltage control is primitive to say the least.
  20. duke37

    Buzzer timing

    Reed switches a quite fast. I have used a reed switch to measure the speed of a shaft up to 1000rpm. In this case, the switch spent most of the time unenergised. Perhaps the magnets are too close together. You could try alternating the magnet polarity so that the field goes through zero.
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