This circuit can be found in automobiles to control the wiper speed, automatic operation of alarm after set time intervals, for automatic dimming of LED in lamps after certain time, in automatic air-coolers, and various applications where certain automatic action has to be done after set time intervals. This circuit is used in various day-to-day applications. Timer circuits are very useful in automation systems where human involvement is not desired. 7555 is also applied as a missing pulse detector. For modulations such as pulse width modulation and pulse position modulation, 7555 is preferred over 555 IC. This IC is also applied for pulse generation, sequential timing and time delay generation. Due to the degradation of resistor and capacitor performances over time, the timer value may not be accurate.ħ555 is usually preferred as timer IC in applications where Precision timing is needed. Power supply between voltages 5v to 15v should be used. In this circuit, the relay voltage should be the same as the source voltage. The diode attached parallel to the relay protects the transistor when the relay is deactivated.Ĭompared to 555 timers, use of 7555 timer works with 8.2 M resistor smoothly. This relay can control any small mechanical device or electronic system. When the transistor goes into saturation state, the relay is activated. The transistor goes into saturation state when the output of the 7555 goes high. Pin-3 of 7555 is connected to the 2N2222 NPN transistor using a 4.7k resistor.
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