Basic 555 Squarewave Oscillator

The following circuit is a Basic 555 squarewave oscillator. Feature : 1 Khz tone, Simple circuitry, limit = 200 mA, inductive voltage reduced, 4.5-9 Supply voltage. Component : 555 timer IC, resistor, capacitor, Speaker, 2N3053 transistor, push button. [qsl.net]

Four-Hour Timer

The following schematic diagram is four hour timer circuit. Feature : easy to build, 3 hours 53 minutes total time,9V supply voltage. Component : 555 timer IC, Resistor, capacitor, switch, transformer, LED, CD4040B, Relay, BC547 transistor, 1N418 diode, variable resistor. [wiredworld.tripod.com]