Relay 3 Click Board™

Product Code: MIKROE-3357

Besides two relays, the Relay 3 Click Board™ contains all the necessary electronic components for driving the relay coils. Two LED indicators provide visual feedback about the activity of the relays. Although it can withstand up to 7A through its contacts, the life expectancy of the relay drops proportionally with the current through the contacts. Therefore, Relay 3 click is a good solution for power or signal switching in a range of low to medium power applications, including domestic appliances, office machines, audio equipment, etc. How Does The Relay 3 Click Board™ Work? The Relay 3 Click Board™ features two SRD-05VDC-SL-C small-size relays, from Songle Relays. These are reliable relays in sealed a plastic housing, offering good isolation. Despite its size, the SRD-05VDC-SL-C relay is able to withstand up to 7A and 220V AC/28V DC. It can endure up to 10 5 operations while loaded, and even up to 10 7 with no load applied. This relay is of a single-pole-double-throw type: when the coil is energized, it will attract the internal switching elements and close one of the contacts, while opening the other contact at the same time.

Normally Closed contacts are usually labelled with NC, while Normally Open contacts are labelled as NO. These relays are designed so that their coils can be easily activated by relatively low currents and voltages. The SRD-05VDC-SL-C relay can be operated with 5V, making it a good choice for activating it by an MCU pin. However, to provide sufficient current for the activation, an additional MOSFET has to be used. Gates of two MOSFETS (one for each relay) are controlled by the MCU pins, therefore are routed to the mikroBUS™. The gates are routed to RST and CS pins of the mikroBUS™ and are labelled as RE1 and RE2, respectively. There are two LEDs (yellow) that are used to indicate the activity state of the relay. When the current flows through the MOSFET, the coil will be energized, and the relay will be activated. This current also flows through these LEDs, indicating that the relay is active. The LEDs are labelled according to the relay they are connected to: REL1 for Relay 1, and REL2 for Relay 2. A Schottky diode is connected across the relay coil, preventing the back-EMF which can be generated because of the inert nature of the coil. The back EMF can have an adverse effect on the circuit and can potentially damage the control circuit. The diode is connected in the inverse direction, allowing the back-EMF to discharge through the relay coil, instead. Each relay is equipped with a 3-pole screw terminal, rated for up to 6A. Therefore, the maximum current through the connected load should not exceed this value. However, as already mentioned above, a high current negatively affects the life expectance of the relay itself, so switching large currents should be avoided. The middle pole of the screw terminal is connected to the common terminal of the relay (COM) while two other poles are the NC and NO contacts of the relay. Having both NC and NO contacts is useful, expanding the implementation possibilities of Relay 3 click. DO NOT TOUCH THE BOARD WHILE THE EXTERNAL POWER SUPPLY IS ON! Note : Relay 3 click has exposed pins/pads. To stay safe take precautions when applying high voltage to the click. The click is to be used by trained personnel only when applying high voltage. SPECIFICATIONS Type Relay Applications Relay 3 click is a good solution for power or signal switching in a range of low to medium power applications, including domestic appliances, office machines, audio equipment, etc. On-board modules SRD-05VDC-SL-C, small-size sealed relays from Songle Relay Key Features Two small-sized SPDT relays in a sealed plastic housing. LED indicators for indicating the activity of each relay. Screw terminals allow secure connection of the load. Protection from back-EMF generated as a result of the coil inductance. Interface GPIO Compatibility mikroBUS Click board size L (57.15 x 25.4 mm) Input Voltage 5V PINOUT DIAGRAM This table shows how the pinout on the Relay 3 Click Board™ corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns). Notes Pin Pin Notes NC 1 AN PWM 16 NC RE1 RST 2 RST INT 15 NC RE2 CS 3 CS RX 14 NC