Understanding Signals - Optiscope- Chapter 3 Activity #1 Problem - no sound wit

John Kauffman

Understanding Signals - Chapter 3 - Activity #1
page 36·in text version 1.0

I'm using homework board and leaving off the breadboard·the 220 resistor

Without the 1 uF cap in the circuit:
- tone from speaker i sheard (although very soft)
- nice image of rough wave on Oscope

When 1 uF cap is added:
- tone stops from speaker
-·Oscop image goes nicely to sine wave.

Why does speaker stop functioning when cap is added?

Andy Lindsay (Parallax)

The first order approximation of the piezospeaker is a small capacitor that makes noise. (A better approximation is a capacitor in parallel with a series RLC circuit, but from the outside, it looks mostly like a small capacitor). Capacitors in parallel create current dividers in a manner similar to resistors in series creating voltage dividers. With resistors in series, the voltage drop is smaller across the smaller resistor. With capacitors in parallel, the amplitude of the AC current into the smaller cap is...smaller, so the piezoelectric element just doesn't have the oomph to vibrate the membrane it's attached to.

Post Edited (Andy Lindsay (Parallax)) : 4/12/2005 3:06:14 AM GMT