Found in a Popular Electronics from the 90s, this circuit uses components that are still current. The circuit triggers the vehicle's horn. The sensors can be increased in number.
This circuit uses only two common transistors and provides good audio power in a speaker. Readers who...
This amplifier step for small signals can use any general-purpose transistor like the BC548. The...
I found this article by my friend A. Fanzeres in a Uruguayan magazine Corriente Alterna in July...