We found this circuit in the Linear Applications Handbook by National Semiconductor. It uses the LM3900, an operational transconductance amplifier as a base. Q1 can be a 2N2222 or similar.
This analog volt-ammeter was found in an Electronics World of 1968. It makes use of a 0-1 mA...
This is one of the many possible siren configurations for the 555 integrated circuit. We found it in...
This circuit was found in an Electronics World magazine from 1990. The circuit can be mounted...