Simple Delay ON Delay OFF Timer Circuit

Did anyone ever wish for timer that turn things OFF after some time but not ON?

Like a smart snooze button for electronics.

In this post we will learn how to make Simple Delay ON Delay OFF Timer Circuit.

This article show:

• List of parts we need
• Full steps to build it
• Small guide how it works
• Tips how to change it for our own need

This circuit is good for people who like to try fun things with electronics.

What is a Delay ON Delay OFF Timer:

A timer circuit or device that wait for some time before turning ON and also wait before turning OFF is called delay ON delay OFF timer.

Some people also call it dual delay timer or delay ON operate delay ON release timer.

This timer has two delay times:

• One delay for turning ON the activation delay
• One delay for turning OFF for deactivation delay

These kind of timers are used in many machines and control systems.

They help to plan actions, control machines and do tasks with time control.

Delay ON Timer Working:

Parts List:

The thing we want to turn ON after some time like the load is connected to the relay.

When we first turn ON the power the electricity goes through a resistor called R2.

But at beginning electricity can not go to one part of the circuit which is called the base of transistor T1 because of another part.

Capacitor C2 acts like a shortcut to ground.

Electricity passes through R2 and it loses some power and starts to charge up C2 like filling a small battery.

When C2 gets enough power the voltage makes transistor T1 turn ON very fast.

This also turns ON another transistor T2 and that switches relay ON.

Now the thing we want to turn ON the load which gets power and the circuit starts working.

The time delay before it turns ON can be changed by using different R2 or C2 values.

Another resistor R1 helps C2 empty fast when power is off so circuit is ready again soon.

Also there is a diode D3 that blocks electricity at right time so everything works correctly.

Formulas and Calculations:

To find the delay ON time in timer circuit that uses resistor and capacitor so we use this formula:

T = 1.1 × R × C

where:

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

In our circuit R1 is 100k ohms and C2 is 220uF.

Now use the formula:

T = 1.1 × 100,000 × 0.00022

T = 24.2 seconds

So the delay time is around 24.2 seconds.

But remember this is just a guess and approximate value.

Actual time can change a bit because of things like resistor or capacitor not being perfect or power not being same all the time.

Also this formula only works with this kind of timer circuit but which might not work for all types.

Note:

If we want to know exact delay time then we can use a stopwatch or oscilloscope.

There are also some online tools or software to help calculate it easily.

How to Build Delay ON Circuit:

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

• First connect one side of resistor R2 to +12V which is the positive side of power.
• Then connect other side of R2 to one leg of capacitor C2.
• Connect other leg of C2 to ground.
• Now take the point where R2 and C2 meet and connect it to base of transistor T1.
• Connect emitter of T1 to ground.
• Connect collector of T1 to +12V.
• Also connect collector of T1 to base of transistor T2.
• Connect emitter of T2 to ground.
• Connect collector of T2 to the relay coil pins.
• Take diode D3 connect its anode to collector of T1 and its cathode to base of T1 which will help with current control.
• Connect one relay contact to the load, with thing we want to turn ON.
• Connect other end of the load to +12V.
• Connect other relay contact to emitter of T2.

Adjustment:

• To change the delay time turn or adjust the variable resistor R2.

Final Check:

• Be sure all wires and parts are connected right and safe.
• Turn ON the power and after short delay then relay should click and load will turn ON.

Delay OFF Timer Circuit Working:

Parts List:

When power is turned ON electricity goes through resistor R2 and starts to fill capacitor C1 like charging a small battery.

As C1 charges it gets more and more power.

When C1 gets enough power it turns ON a small switch transistor.

This small switch then turns ON another switch which starts a timer and this timer uses another resistor and capacitor.

For some time the timer lets C1 recharge again.

When the time is over the capacitor stops the small switch and this cuts OFF power to a relay.

When relay loses its power it opens like a small bridge breaking.

This makes the circuit turn OFF and the connected device also turns OFF.

When we turn the power ON again everything resets and is ready to work again.

Adjustment:

To change the delay time before switch OFF adjust R2 and C1.

Bigger values of R2 or C1 = longer delay time.

The delay depends on the RC values so change them based on how long we want the circuit to stay ON.

Formulas and Calculations:

To find the delay OFF time in timer circuit that uses resistor and capacitor then we can use this formula:

T = 1.1 × R × C

where:

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

In this circuit:

R2 = 1M ohm (1,000,000 ohms)

C1 = 220uF (0.00022 farads)

Now put in the values:

T = 1.1 × 1,000,000 × 0.00022

T = 242 seconds (around 4 minutes)

Note:

This is just a rough guess and actual delay time can change a bit because of power supply, component quality and other things in the circuit.

This formula works for similar type of circuits only.

To check real delay time use a stopwatch or an oscilloscope.

We can also use online timer calculators for easy calculation

How to Build Delay OFF Circuit:

This delay OFF timer circuit is like the delay ON timer, but here we change how the relay works.

Now we use BC547 transistor instead of BC557 and we can add an RC circuit (resistor and capacitor) to make the load turn OFF after some delay.

Connection steps to follow:

• One end of R2 connects to +12V.
• Other end of R2 connects to one leg of C1.
• The other leg of C1 connects to ground.
• Connect the point where R2 and C1 meet to base of T1.
• Emitter of T1 connects to ground.
• Collector of T1 connects to +12V.
• Use BC547 instead of BC557 for T2.
• Collector of T1 connects to base of T2.
• Emitter of T2 connects to ground.
• Collector of T2 connects to relay coil pins.
• Anode of D3 connects to collector of T1.
• Cathode of D3 connects to base of T1 this helps protect circuit from reverse voltage.
• One relay contact connects to the load.
• Other side of load connects to +12V.
• Last relay contact connects to collector of T2.
• Connect ground of circuit to power source ground.
• +12V from power source connects to the positive rail.

Final Check:

• Be sure all wires and parts are connected correctly and safely.

Conclusion:

A simple delay ON delay OFF timer circuit can achieve a versatile function.

These circuits allow to program when a device will switch OFF when the power is cut OFF which is the delay OFF and when it will turn ON when the power comes back which is the delay ON.

They also provide basic functions.

References:

Auto on-off-on delay timer circuit