Using an LDR as a sensor and an operational amplifier this circuit was found in the Encyclopedia of Electronic Circuits volume 5 from 1995. The circuit triggers an optodiac.
This conventional series reducer circuit reduces the voltage of a 12 V battery to the selected value...
In the figure we have a converter that generates a negative voltage from a positive voltage...
This circuit covers the bands from 1.8 to 150 MHz, with plug-in coils whose characteristics are...