Using 555 integrated circuits, this alarm circuit was found in a 90s American documentation. The signal must be applied to a good audio amplifier.
We found this circuit in a 1975 publication. The circuit can be made with BC548 transistors for...
This circuit was found in the December 1992 Radio Electronics magazine. Range depends on optical...
This circuit is from the National Semiconductor CMOS manual of 1977. What this circuit does is to...