C1: (determined value)
R2: (determined value)
IC1: 555 timer IC
SW1: Normally Open Pushbutton
This circuit is a very basic but accurate timing circuit using a 555 timer IC and a few other parts.
It works by discharging a capacitor and then charging it via a resistor. Firstly a low signal is passed to the trigger (2). This activates the discharge pin (7) which discharges the capacitor. When the threshhold pin (6) of the 555 detects the voltage in the capacitor drop to 1/3 vcc, it drives the output pin (3) high. When the capacitor charges to 2/3 vcc, the output pin is driven to low.
A formular is used to determine the values of the capacitor / resistor circuit.
Where T is the time in microseconds, R is component R2 and C is component C1
Very acurate timing is achived with this very simple circuit ranging from a few microseconds to hours.
Any everyday noncrucial timing application. e.g. egg timer, cooking timer, headlight cutout ect ect.
This circuit's timing is independent of the supply voltage but the voltage must not vary. It will operate from 2.5 to 15 volts, draws only a few milliamps and will drive anything up to 200mA from its output.