Posted on May 19, 2012 9842
or built around two CMOS analog switches, which alternatively selects the right and left channels for monitoring and display. The selected signal is amplified by the common-emitter stage Tl, and the output is fed into the string comparators which control the display. These eight comparators are from two LM324 quad op amps, each is connected to a resistor network, which has a 3dB step between each comparator. Each comparator has a positive feedback resistor to increase the hysteresis to provide a longer display, which is switched alternatively at about 10 kHz. The two CMOS switches in line are biased at half the supply voltage by 1- resistors from a 100-KOhmhm divider, which allows them to handle analog signals up to 9 V peak to peak. As the voltage increases above the setpoint of each comparator, the output goes low and the corresponding LED lights, which produces a bar of light in response to the input voltage. For a linear response the resistor-network can be replaced by nine 10-KOhmhm resistors, giving an equal voltage gap before each LED comes on.