The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale limit. The circuit can use other types of warning.
This is the basic configuration of a monostable TTL with the 74121. The trip is done with an NC...
This fixed source configuration with 78xx series regulators has already been explored in several...
In the figure we have a TTL logic interfacing circuit as CMOS logic using a 6N139 optocoupler...