Found in an old Popular Electronics, this circuit warns when a remote lighting system is not working. The circuit uses an LDR as a sensor and the components used are quite common today.
Combining an Ultra-Low Power MCU with an 802.15.4 Radio, the SAM R30 Enables Long-Lasting Battery...
This is a typical common collector amplifier step configuration. The transistor can be used...
This unregulated power supply can source 1.5 A to amplifiers and other circuits. The diodes must...