This circuit uses a PLL4046 oscillator to excite a piezoelectric ceramic. The circuit is from an October 1994 Electronics Now magazine.
This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The...
We found this circuit in an American publication from the 80's translated into Portuguese. The...
We found this circuit in an old French documentation from the 70s, but it can be assembled using...