Did anyone ever wish for timer that turn things OFF after some time but not ON? like a smart snooze button for electronics.
Also, 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
Hence, 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 waits for some time before turning ON and also waits before turning OFF is called a delay ON–delay OFF timer and also some people call it a dual delay timer or a 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
Moreover, many engineers use these timers in many machines and control systems to plan actions, control operations and execute tasks precisely.
Delay ON Timer Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 10k 1/4 W CFR | 2 |
| 100k 1/4 W CFR | 1 | |
| 1M 1/4 W CFR | 1 | |
| Capacitors | Electrolytic 220µF 25V | 1 |
| Semiconductors | Transistor BC547 | 1 |
| Transistor BC557 | 1 | |
| Diode 1N4148 | 1 | |
| Diode 1N4007 | 1 | |
| 12V Relay | 1 |
The device we want to turn ON after some time (the load) connects to the relay and when we first turn ON the power, current flows through a resistor called R2.
At the beginning, another component blocks current, so electricity cannot reach the base of transistor T1.
As a result, capacitor C2 acts like a shortcut to ground and electricity passes through R2 and it loses some power and starts to charge up C2 like filling a small battery.
Also, when C2 gets enough power the voltage makes transistor T1 turn ON very fast and 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.
We can change the turn ON delay by selecting different values for R2 or C2 and R1 helps C2 discharge quickly when the power turns off so the circuit resets sooner.
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:
Also, if we want to know exact delay time then we can use a stopwatch or oscilloscope and also there are 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 and connect other leg of C2 to ground.
- Now take the point where R2 and C2 meet and connect it to base of transistor T1.
- After that connect emitter of T1 to ground.
- Then connect collector of T1 to +12V and also connect collector of T1 to base of transistor T2.
- Also, connect emitter of T2 to ground and connect collector of T2 to the relay coil pins.
- Then take diode D3 connect its anode to collector of T1 and its cathode to base of T1 which will help with current control.
- Now connect one relay contact to the load, with thing we want to turn ON and connect other end of the load to +12V.
- Lastly, connect other relay contact to emitter of T2.
Adjustment:
- To change the delay time turn or adjust the variable resistor R2.
Final Check:
- Always check that all wires and parts connect correctly and safely, then turn ON the power; after a short delay, the relay clicks and the load turns ON.
Delay OFF Timer Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 10k 1/4 W CFR | 1 |
| 100k 1/4 W CFR | 1 | |
| 1M 1/4 W CFR | 1 | |
| Capacitor | Electrolytic 220µF 25V | 1 |
| Semiconductors | Transistor BC547 | 2 |
| Diode 1N4148 | 2 | |
| Diode 1N4007 | 1 | |
| 12V Relay | 1 |
When we turn the power ON, electricity flows through resistor R2 and fills capacitor C1 like a small battery and as C1 charges, it continuously gains more power.
When C1 gets enough power it turns ON a small switch transistor and 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 and when the time is over the capacitor stops the small switch and this cuts OFF power to a relay.
Hence, when relay loses its power it opens like a small bridge breaking and this makes the circuit turn OFF and the connected device also turns OFF.
Finally, when we turn the power ON again everything resets and is ready to work again.
Adjustment:
To change the delay time before, switch OFF and adjust R2 and C1, bigger values of R2 or C1 = longer delay time.
Hence, 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, also this formula works for similar type of circuits only.
To check real delay time use a stopwatch or an oscilloscope and 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:
- First, one end of R2 connects to +12V and other end of R2 connects to one leg of C1 then the other leg of C1 connects to ground.
- Also, connect the point where R2 and C1 meet to base of T1.
- Next, emitter of T1 connects to ground and collector of T1 connects to +12V.
- Now use BC547 instead of BC557 for T2.
- Then collector of T1 connects to base of T2, emitter of T2 connects to ground and collector of T2 connects to relay coil pins.
- Anode of D3 connects to collector of T1 and cathode of D3 connects to base of T1 this helps protect circuit from reverse voltage.
- Also, one relay contact connects to the load and other side of load connects to +12V.
- Last relay contact connects to collector of T2 and connect ground of circuit to power source ground.
- Finally, +12V from power source connects to the positive rail.
Final Check:
- Always check all wires and parts are connected correctly and safely.
Conclusion:
Overall, a Simple Delay ON Delay OFF Timer Circuit can achieve a easy function and also, they provide basic functions.
Furthermore, these circuits let us set when a device turns OFF after the power cuts out (delay OFF) and when it turns ON again after the power returns (delay ON).