The indicator is intended for use with an audio amplifier or preamplifier, but it can also be used in othe
r applications where a number of steps or changes must be counted rapidly. To prevent interference with the audio signal, the circuit is a static design. Thus, if the volume control is not adjusted, the circuit does nothing. The circuit does not need an external clock signal, because this is derived from any changes in the least significant bit (LSB). This is done by two differentiating networks: R9/C1 and R10/C2, which double the frequency of an available LSB signal. Moreover, to ensure that the counters of the indicator remain in step with the volume control, signals "up/down" and "preset" from the preamplifier are used. It might seem rather extravagant to couple the state of the counters in the preamplifier with that of the present counters, but it is a good way to keep the connections between the two units to a minimum. Furthermore, the present counters operate in 8-bit BCD, instead of 6-bit binary as used by those in the volume control (in the preamplifier). All that is required to display the state of the volume control are a couple of BCD-to-7-segment decoders and 7-segment displays. The preset in the indicator must be set in BCD code. Leading zeros are not suppressed so numbers up to and including 9 are displayed, starting with a 0. The DIP switches and resistors Rl through R8 in the diagram can be omitted if only one fixed preset is likely to be used. The resistors should be replaced by jump leads.