We found this circuit in the 1957 Raytheon transistor application manual. The transistor can be a BC558 and the common 6 V relay, just by using this voltage in the supply.
The circuit shown in the figure is quite interesting in control and alarm applications. This...
This circuit was obtained in a transistors manufacturer's manual from the 90s. The circuit uses an...
Originally suggested by Harris in the 1990s, this circuit uses an optical tachometer. The circuit is...