30 Minute Delay Timer Circuit using Transistors

This article explains a simple 30 Minute Delay Timer Circuit using Transistors.

The circuit is with low cost and is easy to build.

It uses common parts like BC547 transistors, resistor and capacitor.

Because of simple design, beginners can also understand it easily.

This circuit is useful where delayed switching is required.

For example, light delay, alarm delay or power control delay.

Circuit Working:

Parts List:

Components	Value	Quantity
Resistors	100Ω, 4.7M	1 each
	Preset 1 Meg	1
Capacitor	Electrolytic 470µF 25V	1
Semiconductors	Transistor BC547 NPN	2
	LED Red, Green	1 each
	Tactile Switch	1
	On Off switch	1
	Battery 3V	1

This circuit works on RC time delay principle.

Here, resistor and capacitor decide delay time and preset allows fine adjustment of delay time.

Two BC547 NPN transistors are used for amplification.

LED1 is used as power indicator and LED2 is used as output status indicator.

Switch is used to start the timing.

Firstly, when switch S1 is turned ON the power is supplied.

At the same time capacitor C1 starts charging slowly through resistor R2.

Because capacitor value is high and charging is slow.

Initially, the voltage at base of Q1 is low and so Q1 remains OFF.

As time passes the capacitor voltage increases gradually.

Then when base voltage reaches transistor turn ON level and Q1 turns ON.

After that Q2 also turns ON because it is driven by Q1 and as a result the LED2 glows after delay time.

Meanwhile the LED1 shows power indication and finally the delay of around 30 minutes is achieved depending on RC value.

Set VR1 preset to maximum value first and then slowly adjust to get exact 30 minute delay.

How to Build:

To build a 30 Minute Delay Timer Circuit using Transistors follow the below connection steps:

• Take all the parts as shown in circuit diagram.
• First, start with Q1 transistor base pin is connected to R2.
• Emitter of Q1 connected to base of Q2.
• Collector of Q1 connected to collector of Q2.
• Then, Q2 transistor base pin is connected to emitter of Q1.
• Emitter of Q2 connected to ground.
• Collector of Q2 connected to collector of Q1 and cathode of LED2 and supply.
• One end of R2 resistor connects to one end of preset VR1.
• Other end of preset connects to base of Q1.
• Capacitor C1 positive end is connected to R2 and switch S2.
• Negative end is connected to ground.
• Resistors R1 is connected to LED1 for current limiting.
• Battery positive goes to switch S1.
• Battery negative goes to ground line.

Conclusion:

This 30 Minute Delay Timer Circuit using transistors is simple and reliable.

It uses very few components and so delay time is easy to change.

Because of transistor based design the circuit cost is low.

Therefore, it is very suitable for hobby and educational projects.

Finally, with proper component selection long delay can be achieved easily.

References:

One month timer circuit