Oscope / Understanding Signals: Why does speaker stop functioning when cap is a

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 is heard (although very soft)
- observe nice image of rough wave on Oscope

When 1 uF cap is added:
- tone stops from speaker
-·observe nice smooth sine wave on Oscop

Why does speaker stop functioning when cap is added?

Nate

1) Are you sure you are using a piezo speaker and not a piezo buzzer?

2) Check the frequency of the sine wave signal on your oscilloscope.· Is it the 200 Hz that it should to be?

Nate

claylj

Without the filter capasitor, the program basiclly sends a 200 Hz square wave to the piezo speaker. Square waves have lots of energy and very strong harmonics which is what you are hearing in the speaker. With the filter, you should have a nice clean sine wave. I so happens that a sine wave at 200 Hz does not have enough energy to drive the piezo speaker. With a normal speaker you should be able to hear the sine wave.

Larry

John Kauffman

I'm using the peiezo speaker that came with the understanding signals kit.

The wave on the Oscope is a perfect 200 Hz.

Based on Larry's reply, if the cap absorbs so much energy that the piezo speaker can not be powered, then I should expect no sound with the cap. Right?

So one of two situations:
I'm still doing something wrong and should be able to hear sound with the cap
- or -
Understanding signals should be revised to note that the two listening steps (p.36 third bullet and p.40 last line) should be done with the cap removed.