This experiment demonstrates how to control a high-power device using a relay and a low-power control signal. Relays act as electrically operated switches, enabling a small control voltage to manage devices that operate at higher voltages and currents.
Experiment Objective
To understand how a relay works and how it can control a high-power load, such as a light bulb or motor, using a low-power control circuit.
Components Required for the Relay Control Circuit
5V Relay Module
Transistor (e.g., 2N2222 or BC547)
1 kΩ Resistor
Diode (e.g., 1N4007)
LED and 330 Ω Resistor (for testing)
DC Power Supply (5V for relay control, appropriate voltage for the high-power load)
Load (e.g., a 12V light bulb or small DC motor)
Breadboard and connecting wires
Relay Control Circuit Setup
Note: Ensure correct polarities for all components and check connections before applying power.
Circuit Diagram and Operation
The circuit uses a transistor to drive the relay, allowing a small control signal to switch on a larger load. The relay coil is connected to the transistor’s collector, with a diode placed across the coil to prevent back EMF from damaging the transistor. The control signal is applied through a resistor to the transistor’s base, which then triggers the relay.
Procedure to Build the Relay Control Circuit
Step 1: Circuit Assembly
Place the transistor on the breadboard. Connect the emitter to ground.
Connect one end of the relay coil to the transistor’s collector.
Connect the other end of the relay coil to the 5V power supply.
Place a diode (1N4007) across the relay coil, with the cathode connected to the 5V side and the anode to the transistor collector.
Connect a 1 kΩ resistor between the control input signal and the transistor base.
Connect the relay’s output terminals to the high-power load circuit (e.g., 12V light bulb or motor), ensuring proper voltage and current ratings.
Step 2: Apply the Control Signal
Apply a low-power control signal (e.g., from an Arduino digital pin or 5V DC power source) to the base of the transistor.
This should activate the transistor, allowing current to flow through the relay coil, switching the relay.
Step 3: Test the Load
Observe the relay’s click sound as it activates.
Check that the load connected to the relay’s output terminals (e.g., the light bulb or motor) turns on when the relay is activated.
Observations
When the control signal is applied, the transistor allows current through the relay coil, closing the relay contacts and powering the load. Observe the relay's response time and any delay in activating the load.
Analysis of the Relay Control Circuit
This circuit demonstrates how a low-power signal can control a high-power load via a relay. The diode protects the transistor from voltage spikes created when the relay coil deactivates. Using a transistor allows the relay to be triggered with a low-current control signal.
Conclusion of the Relay Control Experiment
This experiment illustrates relay-based control of high-power devices. Relays provide an effective way to interface between low-power control circuits and high-power applications, making them invaluable in automation and control systems.
