Doubled-Up Bargraph Display
What could be simpler than comparing two bargraph displays? If you said that one bargraph display is simpler for two signals—you guessed right. This unique circuit switches the inputs of two analog signals and provides a LED bargraph displayed by one driver such as the LM3914 for a linear readout (LM3915 offers a logarithmic display; LM3915, VU display). The circuit may be set to display two dots (see jumper connection data in diagram) 30 that when they coincide and only one dot is seen, the amplitudes of inputs 1 and 2 are about equal. This unusual setup makes for a very interesting and accurate VU display. The clock section is composed of IC3 (4049 chip) that triggers the switch action of IC2 (analog switch).
Should you want to use a format where the bargraph is used with a dot graph, remove jumper 1 and install jumpers 2, 3, and 4. This setup is ideal for watching the RMS value of an audio signal on the bargraph and the peak voltage at that time appears as a dot that will either fall in the bargraph or bounce somewhere above it. This makes for a very unusual display. Remember, with jumper 1 in the circuit, the other jumpers are out; with jumper 1 out of the circuit, the other three are in.
Copyright by Bill Bytheway, K7TTY February 2012