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.
The maximum frequency of the oscillator shown in the figure is around 3 MHz. The trimmer adjusts the...
This circuit was obtained in a 1977 Radio Handbook. The transistor is from the era and the coils...
August 2017 - STMicroelectronics' BlueCoin development environment is available at Mouser...