Using Relays — SIK Circuit 13
Control a relay with a transistor to switch between two LEDs. Learn about electromechanical switching, SPDT relays, Normally Open vs Normally Closed contacts, and flyback protection.
Maagizo
Parts & Introduction
Parts & Introduction
A relay is an electrically-operated mechanical switch. A small current energizes a coil that physically moves a contact arm, switching a separate circuit. Relays can control high-power devices (motors, lights, appliances) from low-power Arduino signals. This experiment uses an SPDT (Single Pole Double Throw) relay to alternate between two LEDs.
Parts Needed
- 1x Arduino Uno + USB cable
- 1x Breadboard
- 1x SPDT Relay
- 1x NPN Transistor (P2N2222A)
- 1x Diode (1N4148)
- 2x LEDs (different colors)
- 2x 330Ω Resistors
- 14x Jumper Wires
Vifaa kwa hatua hii:
SparkFun Inventors Kit - V3.21 kifaa
Arduino Uno R31 kipande
Breadboard1 kipande
NPN Transistor (P2N2222A)1 kipande
Diode (1N4148)1 kipande
5mm LED1 kipande
330 Ohm Resistor2 vipande
Jumper Wires8 vipandeZana zinazohitajika:
Hardware Hookup
Hardware Hookup
Wiring Instructions
Transistor + Relay Coil
- Connect transistor Base through 330Ω resistor to Arduino Digital Pin 2.
- Connect transistor Emitter to GND.
- Connect one side of the relay coil to transistor Collector.
- Connect other side of relay coil to 5V.
- Flyback Diode: Band (cathode) to 5V, anode to Collector.
Relay Contacts + LEDs
- Connect relay COMMON through a 330Ω resistor to 5V.
- Connect relay NC (Normally Closed) to LED 1 positive leg.
- Connect relay NO (Normally Open) to LED 2 positive leg.
- Connect both LED negative legs to GND.
Vifaa kwa hatua hii:
NPN Transistor (P2N2222A)1 kipandeDiode (1N4148)1 kipande5mm LED1 kipande330 Ohm Resistor2 vipandeBreadboard1 kipandeJumper Wires8 vipandeArduino Code
Arduino Code
Open the Arduino IDE and upload the following sketch to your Arduino board.
/*
SparkFun Inventor's Kit
Example sketch 13 — RELAYS
Use a transistor to drive a relay, alternating two LEDs.
Hardware connections:
Transistor BASE through 330 ohm resistor to digital pin 2
Transistor EMITTER to GND
Relay coil: one side to COLLECTOR, other to 5V
Flyback diode: band to 5V, anode to COLLECTOR
Relay COMMON through 330 ohm to 5V
Relay NC to LED 1 positive, Relay NO to LED 2 positive
Both LED negatives to GND
This code is completely free for any use.
*/
const int relayPin = 2;
const int timeDelay = 1000;
void setup()
{
pinMode(relayPin, OUTPUT);
}
void loop()
{
digitalWrite(relayPin, HIGH); // Relay on (COM connects to NO)
delay(timeDelay);
digitalWrite(relayPin, LOW); // Relay off (COM connects to NC)
delay(timeDelay);
}Vifaa kwa hatua hii:
Arduino Uno R31 kipandeZana zinazohitajika:
Test & Experiment
Test & Experiment
What You Should See
You should hear the relay clicking, and see the two LEDs alternating — one on, one off — switching every second.
Troubleshooting
- LEDs not lighting: Check LED polarity — longer leg is positive.
- No clicking sound: The transistor or coil circuit isn't working. Verify transistor orientation and coil connections.
- Relay not making good contact: The SIK relay is designed for soldering, not breadboarding. Press it firmly to ensure all pins contact.
- Confusion: Don't mix up the TMP36 temperature sensor with the transistor!
Experiments to Try
- Replace the LEDs with a motor on the NO contact — use the relay as a motor on/off switch.
- Use a button to control when the relay toggles.
- Add variable delay to create morse code patterns.
Vifaa
9- $105.00
- 1 kipandeKishikilia Nafasi
- 1 kipandeKishikilia Nafasi
- SPDT Relay1 kipande
- 1 kipandeKishikilia Nafasi
- Kishikilia Nafasi
- 2 vipande$3.00
- $5.00
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