![]() INTRODUCTION TO ULN2803 – relay driver IC.Microcontroller interfacing to relays using ULN2003. ![]() ![]() You can read about relay driver ICs here: You can use a relay driver IC to drive multiple arrays from GPIO pins of a microcontroller. Note: Some relay modules also come with an optoisolator as a switching device to provide optical isolation between low and high voltage circuits.īut if you are using a standalone relay without a module and you want to use multiple relays in your projects. By using a switching transistor, we can control the relay from the GPIO pin of a microcontroller. Hence, a switching transistor is used in this relay module to amplify current to the level of the minimum current requirement of the relay coil. But the maximum current sourcing capability of GPIO pins is generally less than 20mA. We usually provide an input signal to a relay from the general-purpose input-output pins of microcontrollers such as Arduino, TM4C123, ESP32, etc. Furthermore, it also provides power to the status LED, power LED and relay coil. It is used to provide input signal and 5V power supply. On the right hand side of the relay module is an input connector. Therefore, a freewheeling diode is used to avoid this effect. When the current passes through an inductive load, it produces an back EMF voltage. The coil used in the relay is an inductive type. Freewheeling DiodeĪ freewheeling diode is connected across the coil to avoid the effect of back EMF. Otherwise, higher voltage may damage the status and power LEDs. Do not connect more than 5V source to Vcc and GND pins of the module. Power LED is also a SMD type and it shows the status of power source connected with the 5V single channel relay module. The DC current passes through a relay coil. In other words, the status LED turns on when the relay is active and the coil is energized through a signal input pin. Status LED is SMD LED which is connected through current limiting resistor and it is available on top right corner of the module. If you are using a high AC voltage and high current load with this module, you should use thick main cables. This 5V relay module supports 10A maximum output current and maximum contact voltage of 250V AC and 30V DC. Each point of the module has screws which make it easy to connect cables and wires with the relay module. Each terminal of the output connector is connected with NO, NC and COM pins of 5V relay. We will discuss the wiring diagram to connect a LOAD and power source with this terminal in later sections of this tutorial. On the left hand of this figure is an output terminal which is used to connect a DC/AC load and DC/AC input power source.
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