This circuit generates pulses whose frequency depends on C1. The circuit can be powered by voltages from 5 to 15 V. We find this configuration in a Signetics manual.
This circuit is from a Radio Electronics from October 1963. The LDR and transistors are from the...
The figure shows how to use an operational circuit as a voltage divider. The circuit is from a...
This is the basic configuration of an operational amplifier as a current regulator. We found it in...