DECIBEL_METER

Published:2009/7/16 4:50:00 Author:Jessie | From:SeekIC

The circuit consists essentially of IC1, the CA3089E, a 0-to 100-μA meter M1, on-off switch S1, a few resistors and capacitors, and a diode. The graph shows the plot of dc volts out of METER OUT, pin 13 of IC1 (33 kΩ to ground), vs. the input signal in microvolts on IF IN 1, pin converted to decibels above 1 mW. IC1 detects the signal level and generates a nearly logarithmic dc output. To linearize the high end of this curve, diode D1 and resistor R6 shunt some of the dc as the voltage on pin 13 rises above 3 V. The battery pack, consisting of eight AA alkaline cells, makes the instrument portable and eliminates the possibility of 50/60-Hz hum interfering with the readings. The meter draws only about 16 mA, so battery life will be long. The meter will provide accurate readings as long as the output of the battery pack remains above 8 V. No regulation of this dc is required.



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