In cases like this, the common circuit diagram would be as follows.įor simple on/off applications, the relay can be connected as shown above. Relay modules like this one are commonly used to drive mains loads from a microcontroller like the Arduino or a sensor. LEDs can be added to this basic circuit to act as indicators, and sometimes even optical isolation is added to the input to further improve the isolation. For this reason, a flyback diode is added anti-parallel to the relay coil to clamp the flyback voltage. The coil is also an inductive load, so when the coil is switched off, a large flyback voltage is developed which can damage the device turning it on and off. This is because although the coil consumes much less current than the currents it can switch, it still needs relatively significant current – low power relays consume around 50mA while higher power relays consume around 500mA. The extra components apart from the relay are there since it would not be possible to drive the relay directly from the pins of a microcontroller. digital logic or a sensor. Internal Circuit Diagram for Single Channel Relay Module This means that the relay can be used to switch mains current through an isolated low voltage digital system like a microcontroller. There are two advantages of this system – First, the current required to activate the relay is much smaller than the current that relay contacts are capable of switching, and second, the coil and the contacts are galvanically isolated, meaning there is no electrical connection between them. This is usually done using the help of a coil that attracts the contacts of a switch and pulls them together when activated, and a spring pushes them apart when the coil is not energized. The relay uses an electric current to open or close the contacts of a switch. The power LED is connected to V CC and turns on whenever the module is powered. The freewheeling diode prevents voltage spikes when the relay is switched off. This way, the input can be driven from a microcontroller or sensor output. The switching transistor takes an input that cannot supply enough current to directly drive the relay coil and amplifies it using the supply voltage to drive the relay coil. The jumper also has the input pin, which when pulled high activates the relay. The input jumper is used to supply power to the relay coil and LEDs. The 'relay status LED' turns on whenever the relay is active and provides an indication of current flowing through the relay coil. The bottom left rating says “10A 30VDC”, meaning the relay can switch a maximum current of 10A DC before the contacts get damaged. For example, the top left marking says “10A 250VAC”, which means the relay can switch a maximum load of 10A when connected to a 250V mains circuit. There are also voltage and current markings, which represent the maximum voltage and current, the relay can switch. The part number of the relay on the bottom says “05VDC”, which means that the relay coil is activated at 5V minimum – any voltage lower than this will not be able to reliably close the contacts of the relay.
Lots of information can be gleaned from the markings on the relay itself.
The second is the relay itself, which, in this case, is a blue plastic case. Adding screw terminals makes it easier to connect thick mains cables, which might be difficult to solder directly. The three connections on the terminal block are connected to the normally open, normally closed, and common terminals of the relay. This is the part of the module that is in contact with mains so a reliable connection is needed. The single-channel relay module is much more than just a plain relay, it contains components that make switching and connection easier and act as indicators to show if the module is powered and if the relay is active.įirst is the screw terminal block. Understanding 5V Single-Channel Relay Module The following are the major components present on a relay module we will get into the details later in this article.ĥV Relay, Transistor, Diode, LEDs, Resistors, Male Header pins, 3-pin screw-type terminal connector, etc.
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