555 Based Adjustable Auto On Off Delay Timer Circuit

Overview
In this tutorial, we will build an IC 555 Based Adjustable Auto On Off Delay Timer Circuit. It is an adjustable delay timer circuit using 555 IC that can automatically turn on/off any output after a fixed duration. Earlier we build
Automatic LED Blinking Circuit
as well as
Flashing Police Light Effect
based on same concept.
The NE555 timer IC is a versatile component widely used in pulse generation and timing applications. The Project 555 timer-based monostable circuit is designed to control a relay for a user-adjustable period. When triggered by a push button, the circuit activates a relay (and an LED indicator) for a specific duration determined by external resistors and a capacitor. This setup is ideal for applications like timed lighting, appliance control, or automation systems.
Components Required
We need following components to build this project.
IC: NE555P timer IC
Resistors: 10K (2)
Resistors: 1K
Potentiometer: 1MΩ
Capacitor: 10µF
Diode: 1N4007
LED
Push Button Switch
Relay (5V/9V coil)
Breadboard
Jumper wires
Power supply (5V–9V)
555 Based Adjustable Auto On Off Delay Timer Circuit
The circuit is structured into four primary functional sections.
First, the
power supply
(5V–9V DC) provides the necessary voltage to the NE555P timer IC, with its ground (Pin 1) and VCC (Pin 8) connected directly to the DC source.
The
timing network
forms the core of the circuit, utilizing a series combination of resistor R1 (10KΩ), potentiometer VR1 (1MΩ), and capacitor C1 (10µF) to determine the output pulse duration. Pin 7 (DISCH) of the 555 IC connects to the junction between R1 and VR1, allowing the potentiometer to adjust the timing interval, while Pins 6 (THRES) and 2 (TRIG) are linked to the capacitor, enabling precise control over the charging and discharging cycles.
The
trigger input
consists of a push button that, when pressed, connects Pin 2 (TRIG) to the ground, initiating the timing cycle. This action transitions the 555 IC into its monostable mode.
Finally, the
output stage
involves Pin 3 (OUT) driving a relay (U0) through resistor R3 (1KΩ), which switches connected AC/DC loads. A flyback diode (D1: 1N4007) protects the relay coil from voltage spikes, while an LED paired with a current-limiting resistor (R2: 1KΩ) provides a visual indication of relay activation.
Working and Testing
In standby mode, the 555’s output (Pin 3) is LOW. Pressing the button pulls Pin 2 (TRIG) LOW, activating the monostable mode.
The output goes HIGH for a duration calculated as:
T = 1.1 × (R1 + VR1) × C1
Adjusting VR1 (1MΩ) varies the delay from
0.11 seconds (minimum)
to
11 seconds (maximum)
. While HIGH, Pin 3 energizes the relay and LED. The relay switches the connected AC/DC load.
Testing Procedure
:
Power Up
: Connect a 5V–9V supply. Ensure the LED and relay remain off initially.
Trigger Test
: Press the button. The LED should illuminate, and the relay should click, staying active for the set time.
Adjust Timing
: Rotate VR1 to test the delay range. Use a stopwatch to verify timing accuracy.
Load Test
: Connect a load (e.g., lamp) to the relay’s output terminals to confirm switching.
Troubleshooting Tips
:
If the relay doesn’t activate, check R3’s value and ensure the relay coil voltage matches the supply.
For unstable timing, verify C1’s polarity and connections.
Ensure D1 is oriented correctly (cathode to +V) to suppress relay coil voltage spikes.
This is how you can make IC 555 Timer Based Adjustable Auto On Off Delay Timer Circuit for multipurpose applications.