NE555 adjustable delay timer relay module is a time-delay switch based on the NE555 timer IC, allowing control of the relay's ON delay from 0 to 10 seconds. The delay can be set via an onboard multi-turn potentiometer. This module helps protect sensitive electronic components and devices from high inrush currents caused by inductive loads during power restoration.
Specification
The quick technical specification of the circuit board is given below.
| Module Type | Adjustable Delay Timer Switch |
| Chip Used | NE555 |
| Input Type | DC |
| Input Voltage | 5V |
| Input Terminal | +VCC, GND |
| Power ON Indicator | Red Light |
| Delay Time Range | Adjustable (0 to 10 Sec.) |
| Load Terminal | COM, NC, NO |
| Load Rating | 10A at 250V AC /10A at 28V DC Max. |
| Relay ON Indicator | Red Light |
| PCB Colour | Red |
Circuit Diagram
Schematic of ne555 adjustable delay timer relay module circuit as shown below.
The components are used in the circuit boards are - U1: NE555 Timer IC, C1: 100UF 50V Electrolytic Capacitor, C2: 100nF 0608 SMD Ceramic Capacitor, PR1: 100K Multi-Turn Potentiometer, RLY1: 5V Relay, Q1: S9013 SMD NPN Transistor, LED1 LED2: 0608 SMD Red LED, R1 R2: 1K 0608 SMD Resistor, D1 D2: 1N4148 SMD Fast Switching Diode, H1: 2-Pin Screw Terminal, and H2: 3-Pin Screw Terminal.
Circuit Working Explanation
The working principle of this adjustable delay timer module is simple and involves a combination of two circuits - A monostable timer circuit based on the 555 timer IC, and a relay driver circuit using a transistor.
When the circuit receives a 5V DC input at Vcc terminal (H1), diode (D1) protects against reverse polarity, and power-ON is indicated by LED (LED1). The 555 timer IC (U1) is configured as a monostable pulse generator. In this configuration, capacitor (C1) charges through potentiometer (PR1) from the 5V supply. When the voltage at the trigger/threshold pins rises from below 1/3 Vcc to above 2/3 VCC, the timer output remains high for a duration (0 to 10 Seconds) determined by the adjustable potentiometer. Capacitor (C2) stabilizes the control voltage.
The timer output is then used as an input signal to the base of the N-channel transistor (Q1) via a turn-ON indicator LED (LED2) and a current-limiting resistor (R2). When the input signal is high (≤ 4V), the transistor becomes forward biased and lets current flow from collector to emitter.
The relay (RLY1) coil is connected between +VCC and the collector of transistor (Q1). When the transistor is ON, current flows through the relay coil, energizing it and changing the state of the relay contacts — NO and COM contacts close, and NC and COM contacts open. These contacts are used to turn ON or OFF the load connected at terminal (H2).
A flyback diode (D2) is connected in parallel with the relay coil to protect the transistor from high-voltage spikes generated when the relay coil is turned off.
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