This sophisticated moving bar indicator circuit with the LM3915 is from a Radio Electronics magazine from May 1985. The two-channel circuit includes the power supply.
The 1 kHz tuned filter shown uses a 741 op-amp. The components can be re-scaled to suit the...
This voltmeter for continuous voltages has several scales and is totally passive. The diodes are...
The sensitive relay reed trigger transistors can be the BC548 and the diode can be the 1N4148. The...