Apr 09

Oscilloscope and oscillators



Ohms Lawresistors in series and parallelmass and weight and 555Guest Keith Gudger brought his digital storage oscilloscope to demonstrate. Max brought his State Science Fair-bound project to the be first subject of the oscilloscope.  Max has improved his energy-gathering soccer ball since we last saw it, now using 5 piezoelectric transducers, each with its own bridge rectifier to charge a single capacitor.  The scope showed a positive spike followed by a negative swing and no ringing after each flex of a transducer.

We introduced Ohm’s Law for new students and reviewed it for old.  While Max and Keith analyzed the soccer ball, Carlin, Rhys, and Maverick wired 555 chips to flash an LED.  Keith then connected his oscilloscope to one of the circuits (between the LED dropping resistor and the LED) to reveal a sharp square wave.  I gave students a 22 microfarad capacitor to incorporate into their output circuit, and each chose a different location: A) from cathode of LED to ground, B) across the LED, and C) between the anode of the LED and +5V.  Circuits A and B both continued to blink, but showed attack and decay (like a shark fin) on the oscilloscope.  Circuit C stopped blinking and showed no activity on the oscilloscope.  We speculated that circuit C charged the capacitor but did not discharge it, as A and B did, so it blocked all further current flow through the LED.

555 oscillator with 3 capacitor placementsoscilloscope traces

Electronics was hard work, so we adjourned to the front yard to run around with pool noodles.  After working off some energy, we watched the first 15 minutes of Wonders of Life episode 1, pausing frequently to discuss topics sparked by the video.  This led to energy, potential gravitational energy, and what would happen if we could drill a tunnel through the earth. We concluded that in the absence of friction or physical damage to extreme temperatures in the core, we would emerge in the Indian Ocean, moving about as fast as when we stepped off the edge here.  Conservation of energy brought us to that conclusion after we talked about E=mc² to account for matter + energy being conserved.

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