Simple Delay ON Delay OFF Timer Circuit

Have you ever wanted a timer that turns things off instead of on after a certain amount of time?

Like a fancy snooze button for your electronics.

This post shows you how to build this kind of timer circuit.

The post includes:

• A list of parts you will need
• Step by step instructions on how to build it
• An explanation of how the circuit works like a mini lesson.
• Tips on how to change it for your own projects

This is a great circuit for anyone who wants to get creative with electronics.

What is a Delay ON Delay OFF Timer:

A Delay ON Delay OFF Timer also known as a dual delay timer or a delay on operate, delay on release timer, is an electronic circuit or device that provides a predefined time delay for turning on and off a load.

It consists of two separate delay periods: one for the activation ON delay and another for the deactivation OFF delay.

These timers are commonly used in various industrial and control applications for sequencing events controlling equipment or managing processes with specific time delays.

Delay ON Timer Working:

Parts List:

The thing you want to turn on after a delay the load is plugged into the relay.

When you first turn on the power, electricity flows through a resistor R2.

At first the electricity can not get to a part of the circuit the base of transistor T1 because another part capacitor C2 acts like a shortcut to ground.

The electricity goes through R2 losing some power and starts to fill up C2 like a battery.

Once C2 has enough power voltage to turn on transistor T1 it flips on really quickly.

This turns on another transistor T2 which activates the relay.

Finally, the thing you want to turn on the load gets power and the circuit is complete.

The delay time before the load turns on can be adjusted by changing the resistor R2 and capacitor C2.

Another resistor R1 helps C2 empty quickly so the circuit is ready to go again soon.

There is also a diode D3 that helps block electricity at certain times in the circuit.

Formulas and Calculations:

Formula used to calculate the delay on time for timer circuits that uses a capacitor and resistor which is mentioned below:

T = 1.1 * R * C

where,

• T is the time delay in seconds
• R is the value of the timing resistor in ohms
• C is the value of the capacitor in farads

In the above circuit, the timing resistor is R1 100k and the capacitor is C2 220uF.

By using the below formula, you can calculate the approximate delay time of the circuit which is as follows:

T = 1.1 * 100,000 * 0.00022

T = 24.2 seconds

It is crucial to remember that this is only an estimate.

Due to several factors including component tolerances and power supply voltage, the circuits actual delay time may vary slightly.

Furthermore, this formula might not work with different delay on timer circuits and is limited to the particular circuit configuration.

Note:

An oscilloscope or stopwatch can be used to measure the precise delay time of your circuit.

Another option is to use internet calculators or simulation programs made specifically for timer circuits.

How to Build Delay ON Circuit:

To build a Simple Delay ON Delay OFF Timer Circuit follow the below mentioned steps:

• Connect one end of resistor R2 to the positive terminal of the power source 12V.
• Connect the other end of R2 to one leg of capacitor C2.
• Connect the remaining leg of C2 to the ground.
• Connect the junction of R2 and C2 to the base of transistor T1.
• Connect the emitter of T1 to the ground.
• Connect the collector of T1 to the positive terminal of the power source 12V.
• Connect the collector of T1 to the base of transistor T2.
• Connect the emitter of T2 to the ground.
• Connect the collector of T2 to the coil terminals of the relay.
• Connect the anode of diode D3 to the collector of T1.
• Connect the cathode of D3 to the base of T1.
• Connect one of the relay contacts to the load.
• Connect the other end of the load to the positive terminal of the power source 12V.
• Connect the remaining relay contact to the emitter of T2.

Adjustment:

• Adjust the variable resistor R2 to set the desired delay period.

Final Check:

• Ensure all connections are secure.
• Power on the circuit and observe the relay activation after the set delay.

Delay OFF Timer Circuit Working:

Parts List:

When you turn on the power electricity flows through a resistor R2 and starts filling up a capacitor C1 like a battery.

As the capacitor C1 fills up, it gets more and more power.

This keeps happening until it has enough power to turn on a tiny switch (transistor).

This tiny switch turns on another switch, which also turns on a timer made with another resistor and capacitor.

The timer lets the capacitor fill up again for a specific amount of time.

Once that time is up, the capacitor stops the tiny switch, which cuts off power to a special relay switch.

The relay switch acts like a bridge and when it loses power, the bridge opens.

This cuts off power to whatever device is connected to the circuit turning it off.

Finally, everything is ready to start over again when you turn on the power next time.

Adjustment:

• The delay period for turning the load off can be adjusted by varying the values of resistor R2 and capacitor C1.
• Higher values of R2 or C1 will result in longer delay periods.
• The values of resistor R2 and capacitor C1 in the RC circuit also affect the delay for turning the load off.
• Adjust these values based on the desired delay.

Formulas and Calculations:

Formula used to calculate the delay off time for timer circuits that uses a capacitor and resistor which is mentioned below:

T = 1.1 * R * C

where,

• T is the time delay in seconds
• R is the value of the timing resistor in ohms
• C is the value of the capacitor in farads

In the above circuit, the timing resistor is R2 1M and the capacitor is C1 220uF.

By using the below formula, you can calculate the approximate delay off time of the circuit as follows:

T = 1.1 * 1,000,000 * 0.00022

T = 242 seconds (or about 4 minutes)

Note:

This is a rough estimate, the power supply voltage, component tolerances and other circuit factors may cause variations in the actual delay duration.

Circuits with a similar design to the one you supplied can use this formula.

With an oscilloscope or stopwatch, you can measure the precise delay time of your particular circuit.

As an alternative, you can look into online calculators and simulation tools made specifically for timer circuits.

How to Build Delay OFF Circuit:

The delay OFF timer circuit you are describing is a variation of the delay ON timer but with a different relay driver configuration.

In this case, the relay driver BC557 is replaced by BC547 and an RC circuit is used to introduce a delay for turning the load off.

Below are the key modifications to the circuit:

Circuit Construction:

Connect R2 and C1:

• Similar to the delay ON timer connect one end of resistor R2 to the positive terminal of the power source 12V.
• Connect the other end of R2 to one leg of capacitor C1.
• Connect the remaining leg of C1 to the ground.

Connect T1:

• Connect the junction of R2 and C1 to the base of transistor T1.
• Connect the emitter of T1 to the ground.
• Connect the collector of T1 to the positive terminal of the power source 12V.

Connect T2 :

• Replace BC557 with BC547 for T2.
• Connect the collector of T1 to the base of transistor T2.
• Connect the emitter of T2 to the ground.
• Connect the collector of T2 to the coil terminals of the relay.

Connect D3:

• Similar to the delay ON timer connect the anode of diode D3 to the collector of T1.
• Connect the cathode of D3 to the base of T1.

Connect the Relay Contacts:

• Connect one of the relay contacts to the load.
• Connect the other end of the load to the positive terminal of the power source 12V.
• Connect the remaining relay contact to the collector of T2.

Power Supply:

• Connect the ground to the ground of the power source.
• Connect the positive terminal of the power source to the positive rail.

Adjustment:

• Adjust the variable resistor R2 to set the desired delay for turning the load off.

Final Check:

• Ensure all connections are secure.
• Power on the circuit and observe the relay activation and delayed switch off action.

With these modifications the circuit will now provide a delayed switch off action for the connected load controlled by the adjustment of R2 and the characteristics of the RC circuit introduced for the delay OFF function.

Conclusion:

A flexible function can be achieved with a basic delay on delay off timer circuit.

These circuits provide basic functionality, but they also let you set the time before a device turns off after power is removed (delay off) and when it turns on after power is restored (delay on).

References

Auto on-off-on delay timer circuit