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. Pin-7, DISCHARGE, is the discharge output of the timing capacitor.Pin-6, THRESHOLD, is the input pin for lower voltage sense of the timing capacitor.Pin-5, CONTROL_VOLTAGE, this pin is for setting the upper voltage sense of the timing capacitor.Pin-4, RESET, is the timer inhibit input.Pin-3, OUTPUT, is the timer logic output pin.Pin-2, TRIGGER, is the start timer input pin.Pin-1, GND, is the ground pin also used for low level 0.By changing the switch positions adjustable timers for 5,10, 15, 20, 25, 30 minutes can be formed.
For designing a 30 Minute Timer using 7555, five resistors, each of 8.2 M are used along with a capacitor of 33♟. 7555 works as a monostable multivibrator. The specified time is set using the external resistor and capacitor. By adjusting the values of external resistor R1 and Capacitor C1, adjustable timer circuits can be designed.ħ555- Timer is available as an 8-pin package. The output from the 555 IC is drawn from the Pin-3. Circuit Diagramģ0 Minute Timer Circuit can be designed using a 555 Timer IC in Monostable Mode. This feature of 555 Timer is used to design the Adjustable Timer circuits. As this state is unstable, the output goes high as soon as the interrupt passes. When an interrupt occurs the output enters into an unstable state.i.e. When the user sets stable output as high, the output of the timer will be high until any interrupt occurs. In this mode, the output of 555 IC has two states – a stable state and unstable state. 555 Timer operates in three modes – A- stable, Monostable, and Bistable modes.įor 30 Minute Timer circuit, 555 IC is operated in Monostable mode.
This IC when used as an oscillator, provides time-delays.
555 timer IC is used in the timer circuit. In 30 Minute Timer project, a timer is constructed which make a count down from 30-minute mark to the 0-minute mark.
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