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Lightning Detector

Lightning Detector. Michael Bloem December 5, 2002 Engr 311. The Circuit. The purpose of the circuit is to set off an LED when there is a lightning strike in the area (even if too far away to be seen) This will indicate the proximity and intensity of a storm. Circuit Operation: Input Stage.

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Lightning Detector

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  1. Lightning Detector Michael Bloem December 5, 2002 Engr 311

  2. The Circuit • The purpose of the circuit is to set off an LED when there is a lightning strike in the area (even if too far away to be seen) • This will indicate the proximity and intensity of a storm

  3. Circuit Operation: Input Stage • A lightning strike is approximated by a small voltage pulse • The circled part of the circuit is resonant at 300 kHz, so that is the frequency passed through the circuit

  4. Circuit Operation: Input Stage • This is the Fourier transform of the pulse current input and the input to the base of the first transistor • Note that the pulse has components at all frequencies • Also note that the input stage of the circuit picks out the 300 kHz part and sends it to the circuit

  5. Circuit Operation: Input Stage • The first transistor provides amplification of the signal before it is sent to the flasher part of the circuit

  6. Circuit Operation: Flasher • The second transistor is biased by adjustment of the variable resistor so that it doesn’t allow current to flow until a radio burst pulls the base down

  7. Circuit Operation: Flasher • Once the second transistor’s base is pulled down, it turns full on and current flows as shown by the red arrows • This sends a relatively strong current to the third transistor • This current flows until the capacitor discharges to ground • Then, the current from the diode flows to the capacitor to charge it again to be ready for the next pulse (green arrows)

  8. Circuit Operation: Flasher • The third transistor should amplify the current and send it on to the LED driver

  9. Circuit Operation: LED Driver • The LED driver sends a current pulse to the LED, lighting it up.

  10. Circuit Simulation Output • To simulate a lightning strike in Cadence, I just used a small (.01 V) and short (2.5us) voltage pulse. • Why the output is good: it does create a current pulse that starts when the lightning strike occurs and then goes away • Why the output is bad: • Sinusoidal response- the capacitor should discharge fast enough so that it is just a pulse • Too small of a current to set off an LED

  11. Physical Implementation • I have found all the parts for this circuit and put them together on a breadboard • Testing • To approximate a lightning strike • Van de Graaf machine • Square wave from function generator • Result of testing • Essentially the same results as from Cadence- the current that ends up at the LED is too small

  12. Problems Opportunities for Improvement • Get enough current to light up the LED • Change the biasing of the amplifying transistors (2nd and 3rd transistors) so they actually amplify • Add my own amplification component at the output • Opamp or transistor • Get the current to be a single pulse rather than a sinusoid • Play with the capacitor value • Not as important- still get an LED flash with the sinusoid

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