Time Delay Relay Description:
Time Delay Relay using 555 Timer– In this tutorial, you will learn how to turn ON a relay for a specific time using 555 Timer and a few electronic components like resistors, capacitors, and diodes. The Time Delay Relays can be used in hundreds of different types of electronic and controller based projects. In this project, I have used a Pushbutton which is used to turn ON the relay for the specified time. A variable resistor or Potentiometer is used to adjust the time. This is a low cost and purely electronics-based project. This is the cheapest and simplest automatic relay controller circuit.
Advanced Time Delay Relays can be designed using programmable controllers.
In my previous tutorial I designed a project “Control anything on Time Basis”, this project was based on the Atmega328 microcontroller, this is the same microcontroller which is used in Arduino Uno Board. With the help of this project, you can turn ON anything, for more details read my article on “Control Anything on Time basis”.
Later, I designed an advanced version of the same project “Advanced Countdown Timer”.
This countdown timer can be used as the end product. With the help of this Countdown timer, you can control different types of electrical loads like for example Light Bulbs, Heaters, Water Pumps, Washing Machines, Fans, etc. in fact, this countdown timer can be used anywhere where you need to control anything on the time basis. This countdown timer is ideal for AC and DC loads.
Using this Arduino based countdown timer is very simple; the instructions are displayed on the 16×2 LCD. The user simply enters the time in minutes and seconds and press the Asterisks “*” key on the Keypad. The total time is displayed in seconds. The timer is started which is based on the millis function. The load which is connected with the relay is turned ON. This load will remain ON until the total seconds decrements to 0.
If at any time you need to change the minutes and seconds, you can simply press the Hash “#” key on the keypad which will take you back to the main screen, and you can start again by entering the minutes and seconds.
So, if you want more control over the relay then you should read my above articles. Anyhow, let’s continue with our original topic “Time Delay Relay using 555 Timer”. Before, I am going to explain the Time Delay Relay circuit diagram, I highly recommend reading my article on the 555 Timer IC, which covers all the basics. After reading my article on the 555 Timer IC then you can resume from here.
Without any further delay, let’s get started!!!
The components and tools used in this project can be purchased from Amazon, the components Purchase links are given below:
*Please Note: These are affiliate links. I may make a commission if you buy the components through these links. I would appreciate your support in this way!
Why we need the 555 Timer IC?
It is very simple to generate delays using the Arduino Uno, Arduino Mega, Arduino Nano, PIC microcontroller, etc. But there are situations when we prefer the 555 Timer IC and this is because, the 555 Time is cheap, easy to use, durable, no programming is needed, and so many other factors. Let me give you an example.
Let’s say you want to make an Automatic Street Lights control system using Arduino. Now, you can do this project using the Arduino Uno or any other controller board. You can easily interface the LDR and a relay module with the Arduino. But you know it will increase the overall project cost. Nobody is going to purchase such a costly circuit. On the other hand, the same project can be done using the 555 Timer IC.
IC 555 Pin Diagram / Description / configuration / Pinout:
A standard 555 Timer IC package includes 25 transistors, 15 resistors, and 2 diodes on a Silicon chip installed in an 8-pin mini DIP ”dual-in-line package”. Two other packages of the Timer ICs are available which are 556 and 558. The 556 Timer IC has 2 timing circuits “Dual Timer”, while the 558 Timer IC has a total of 4 timing circuits “Quad Timer”. But in this article, we will only discuss the IC 555 timer. As you can see in the picture above, the 555 Timer IC has a total of 8 pins which are clearly labeled as GND, TRIG, OUT, RESET, CTRL, THR, DIS, and Vcc. Let’s talk about each pin in detail.
555 Timer IC Pins description:
- GND “Ground”:
Ground reference voltage, low-level 0V.
- TRIG “Trigger”:
The OUT pin 3 goes high and a timing interval starts when this input falls below ½ of CTRL voltage which is typically 1/3 Vcc, CTRL being 2/3 Vcc by default if CTRL is left open. In other words, the OUT pin remains high as long as the trigger is low. The output of the IC 555 timer totally depends on the amplitude of the external trigger voltage applied to this pin.
This output is driven to approximately 1.7V below +Vcc, or to GND.
A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET pin of the NE555 Timer IC rises above approximately 0.7 volts. Overrides TRIG which overrides threshold.
- CTRL “Control”:
Provides control access to the internal voltage divider (by default, 2/3 Vcc).
- THR “Threshold”:
The timing (OUT high) interval ends when the voltage at the threshold pin is greater than that at the CTRL pin (2/3 Vcc if CTRL is open).
- DIS “Discharge”:
Open Collector output which may discharge a capacitor between intervals. In phase with the output.
Positive supply voltage, which is usually between 3 and 15 volts.
555 Timer IC Features:
- High Current Drive Capability (200mA)
- Adjustable Duty Cycle
- Temperature Stability of 0.005%/ °C
- Timing From µSec to Hours
555 Timer IC Applications
- Precision Timing
- Pulse Generation
- Time Delay Generation
- Sequential Timing
555 Timer IC Working:
The 555 Timer has three modes of Operation which are
- Bistable Mode
If you want to study the different modes of operation then read my article on 555 Timer IC.
555 Timer based Time Delay Relay Circuit Diagram:
For the best understanding let me share with you the inside diagram of the 555 Timer IC.
In this Time Delay Relay Circuit, the 555 Timer is used in the Monostable Mode. No doubt the heart of this circuit is 555 Timer IC. The other main components are the resistors R1, R2, Pushbutton S1, Capacitors C1, C2, Diodes, and a 12V SPDT type relay.
As you can see R2 is connected in series with a capacitor C2, this is an electrolyte capacitor. The positive leg of the capacitor is connected with the resistor while the Gnd leg of the capacitor is connected with the ground.
The discharge pin and the non-inverting input of the first voltage comparator are connected between the R2 and C2. The Vcc is 12v. One side of the resistor R1 is connected with the Vcc while the other side of the R1 is connected with the Switch S1, while the other side of the S1 is connected with the Ground. A wire from the middle of the R1 and S1 is connected with the inverting input of the 2nd voltage comparator which is the Trigger pin of the 555 timer IC.
When the switch is open R1 keeps the trigger input High by connecting it with the Supply voltage Vcc. Due to this the voltage on the inverting input will be greater than the voltage available on the non-inverting input which is 1/3 Vcc. So the output of the 2nd voltage comparator will be zero 0 which is given as the input to the Flip-Flop S pin. We get 1 at the Q bar which turns on the Transistor and discharges the capacitor C2. So this way the voltage available at the inverting input of the 1st voltage comparator “2/3 Vcc” is greater than the voltage available on the non-inverting input. Due to this the output of the 1st voltage comparator will also be zero “0”. So, the Output of the 555 Timer IC remains LOW.
To make the output of the 555 Timer IC High, or in simple words to turn ON the relay, we need to press the Switch S1 which is a push-button. The time we press the switch S1 the trigger pin is pulled low and the comparator outputs 1 which is given as the input to the Flip-Flop. The Q-bar gives 0 which keeps the transistor off, due to which now the R2 will charge the Capacitor C2, meantime the output of the 555 Timer IC remains High. As the capacitor is charged and the voltage reaches 2/3 Vcc the Output of the 555 timer goes low.
So the ON time of the 555 timer depends on the value of the resistor R2 and the capacitor C2. Large value capacitors will take a lot of time to charge. We can calculate the time by using the following formula.
T = 1.1 * C2 * R2.
So the delay time can be adjusted using the potentiometer R2, you can also use a fixed value resistor if you want to keep the delay time constant.
This Time Delay Relay can also be used in security projects. You can replace the Pushbutton with a PIR Sensor, IR sensor, or any other sensor, when the sensor is activated it will turn ON the buzzer or Light for the specified time. You can connect AC or DC loads with the 12 Relay. So that’s all about the Time Delay Relay Circuit.
Time Delay Relay Proteus Simulation:
Before testing my Time Delay Relay circuit on the Breadboard, first I designed a Proteus simulation. I was able to adjust the ON time using the variable resistor or potentiometer. I successfully controlled the relay.
Relay Turned ON when I pressed the switch:
Relay turned OFF when the time was completed:
At this point, I was pretty confident with the connections.
After this, I did all the connections on the Breadboard and it worked in the same way. I varied the time duration, I could hear the relay tick sound. Now the final step was to design the PCB board.
Following the same exact connections, I designed a PCB for the Time Delay Relay based on the 555 Timer and 12V SPDT type relay. You can clearly see all the connections. To make the design elegant and to fast the PCB etching time; I applied the Ratnest command.
More about the Time Delay Relays:
Time-delay, or time-release relays, allow necessary actions to happen at specific times in an electrical apparatus because they, in essence, act as a timer. The purpose of time-delay relays is to start or stop currents from moving in coils and armatures, the moving parts of electrical mechanisms. They are designed to allow electrical circuits to release at certain times. These types of relays are triggered either by the opening and closing of a signal or by input currents. Time-delay relays are extremely useful in many of today’s modern electrical devices. For instance, one time-delay relay used in combination with another can delay the powering up of some parts of conveyor belts. Because conveyor belts need to work in concert with each other, but all parts are not supposed to work at the same time, time-delay relays are utilized so that different parts start up at different times. If time-delay relays were not used in conveyor belts, items would pile up on top of each other, instead of moving from one working conveyor belt to the next at the proper time when needed.
Another application of time-delay relays is in the use of many of today’s lamps that turn themselves on and off at specified times. Christmas lights and traffic signals are excellent examples of time-delay or time-release relays being used to switch lights either on and off or to turn signals from one position to another. In these types of applications, more than one time-delay relay is necessary in order to give lights uniform frequency and measure time for the desired light application. Another useful operation of time-delay relays is when used for safety reasons. For instance, in furnaces and furnace fans, the furnace’s combustion chamber must be in use before the furnace is lighted in order for the fan to blow away fumes that can explode the furnace if a time delay did not prevent it. Time-delay relays are used in this instance in order to allow ventilation of the combustion chamber to avoid gaseous vapors or explosion. Motors that must begin slowly are another example of time-delay relays. These relays are used in motors that must start slowly in order to be activated slowly and use much less power than if the machine is started up all at once. Industrial machinery often must be started up slowly with time-delay relays because, without them, industrial machines would generate an enormous amount of power if started up all at once. This would not only use up a huge amount of power every time they must be started, but it could cause dangerous conditions because of the amount of current being used.
I hope, you have learned something new. If you have any questions regarding this article, let me know in a comment.