5 To 20 Minutes Alarm Timer Circuit

Time control is very important in out daily life.

Sometimes we do forget small tasks.

So this 5 To 20 Minutes Alarm Timer Circuit helps us remember.

It gives alarm after a fixed time as the circuit uses popular IC 555 timer.

Time can be selected from 5 to 20 minutes by just pressing start and relax button.

After time is complete, the buzzer sounds.

The circuit is simple and with low cost and it works on 9V battery which is very easy to build.

This circuit is best for beginners and hobby projects.

Circuit Working:

Parts List:

Circuit working for 5 Minutes Timer:

The above IC 555 circuit is in monostable mode.

When power is ON the circuit does nothing.

When Start button S1 is pressed then pin 2 goes LOW.

This starts the IC1 555 by output pin 3 going HIGH and buzzer turns ON.

Capacitor C2 starts charging through resistor R2.

After set time is over the capacitor becomes fully charged.

Output pin 3 goes LOW and buzzer turns OFF automatically.

Timer resets itself and waits for next start.

Circuit Working for 5 to 20 Minutes Timer:

This above circuit also works in monostable mode.

Different resistors are used to change timing.

Selector switches S3 to S6 select different resistors.

Each resistor gives different delay time.

• 5 minutes uses 470k resistor
• 10 minutes uses 1M resistor
• 15 minutes uses 1.5M resistor
• 20 minutes uses 2.2M resistor

When S2 Start button is pressed then timer starts.

The selected resistor controls charging speed of capacitor.

After selected time the output goes LOW and buzzer stops automatically.

Formulas:

Timer Formula:

Time delay formula for IC 555 monostable mode

T = 1.1 x R x C

where,

• T is the time in seconds
• R is the resistance in ohms
• C is the capacitance in farads

How to Build:

To build a 5 To 20 Minutes Alarm Timer Circuit following are the steps we need to follow for connections:

IC1 555 Pin Connection for 5 Minutes Timer Circuit:

• Assemble all the parts as shown in circuit diagram.
• Pin 1 Ground connect to battery negative.
• Pin 2 Trigger and pin 4 Reset connect between S1 start push button and resistor R1
• Pin 3 Output connect to buzzer negative and positive of buzzer connect to positive supply.
• connect directly to VCC.
• Pin 5 Control Voltage connect to C1 capacitor and GND.
• Pin 6 Threshold connect to positive terminal of C1 capacitor.
• Pin 7 Discharge connect to R2 resistor.
• Pin 8 VCC Connect to battery positive.
• Connect switch S2 to positive of 9V battery

IC2 555 Pin Connection for 5 to 20 Minutes Alarm Timer Circuit:

• Pin 1 Ground connect to battery negative.
• Pin 2 Trigger connect between positive supply and resistor R1
• Pin 3 Output Connect to buzzer negative and positive terminal connect to positive supply.
• Pin 4 Reset connect to one end of S2 start switch and other end of switch to GND.
• Pin 5 Control Voltage connect to C1 capacitor and ground.
• Pin 6 Threshold and Pin 7 Discharge connect to positive terminal of timing capacitor C2 and GND.
• Pin 8 VCC Connect to battery positive.
• Connect resistor R2 to R5 in series with S3 to S6 switch from positive supply to pin 6 and 7 of IC2

Conclusion:

The 5 To 20 Minutes Alarm Timer Circuit using IC 555 is very useful project.

It is simple and reliable as the timing can be changed easily using resistors.

This circuit is best for beginners and students and it can be used in many daily life electronic projects.

References:

How can I make a 15 minute egg timer circuit?