FIXED_FREQUENCY_GENERATOR

Published:2009/7/7 1:25:00 Author:May | From:SeekIC

A single op amp, one fourth of an LM324 quad op amp, is configured as a standard inverting ampli-fter. At power up, a positive voltage is applied to the noninverting input of U1, via R3, forcing its output high. That high output travels along three paths. The first path is the tone output. Along the second path, by way of R5, that high is used as the drive signal for BZ1. In the third path, the high output of U1 is fed back, via R4, to the inverting input of U1. That forces U1's output to go low. And that low, when fed back to the inverting input of U1, causes the op amp output again to a high, and the cycle repeats itself. As configured, U1 provides a voltage gain of 4.7 (gain R4/R1).The outer ring of the piezo element is usually connected to the circuit ground. The large inner cir-cle serves as the driven area, and the small elon-gated section supplies the feedback signal. Resistor R5 sets BZ1's output-volume level. That level can be increased by decreasing R5 for example, to 470 Ω. To decrease the volume, increase R5 to about 2.2 KΩ, or so.Resistors R2 and R3 set the bias for op amp ,U1's positive input pin 3 to half of the supply-voltage level. That allows for a maximum voltage swing at U1's output. Although a quad op amp is specifted, almost any similar low cost single or dual op amp will work for U1a.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Signal_Processing/FIXED_FREQUENCY_GENERATOR.html

Print this Page | Comments | Reading(3)