Relay 3 Click
PID: MIKROE‐3357 Weight: 42 g
Relay click 3 is a dual relay Click board, featuring two single-pole doublethrow relays which can be operated by output pins of the host
microcontroller (MCU). It offers an elegant and easy solution for controlling a
wide range of power applications. Two SRD-5VDC-SL-C relays used on this
Click board™ are hermetically sealed relays which require 5V across their
coils while consuming about 0.4W while active. They allow up to 28VDC
across the connected load, while conducting up to 7A. Relay 3 click can be
used in various PLC-based systems, as a remote ON/OFF switch, and other
similar applications.
Relay click 3 is supported by a mikroSDK compliant library, which includes
functions that simplify software development. This Click board™ comes as a
fully tested product, ready to be used on a system equipped with the
mikroBUS™ socket.
Besides two relays, the 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 it work?
Relay click features two SRD‐05VDC‐SL‐C small-size relays, from SongleRelays.
These are reliable relays in a sealed 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 105 operations while loaded, and
even up to 107 with no load applied. This relay is of a single-pole-doublethrow 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 labeled with NC, while
Normally Open contacts are labeled 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 labeled as
RE1 and RE2, respectively.
There are two LEDs (yellow) which 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 labeled
according to the relay they are connected to: REL1 for the Relay 1, and REL2
for the 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 the 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, 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.
ON!
DO NOT TOUCH THE BOARD WHILE THE EXTERNAL POWER SUPPLY IS
Note: Relay 3 click has exposed pins/pads. To stay safe take precaution 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
Input
Voltage
5V
Click board
size
L (57.15 x 25.4 mm)
Pinout diagram
This table shows how the pinout on Relay 3 Click 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
NC
4
SCK
TX
13
NC
NC
5
MISO
SCL
12
NC
NC
6
MOSI
SDA
11
NC
NC
7
3.3V
5V
10
+5V
Power Supply
GND
8
GND
GND
9
GND
Ground
Ground
Relay 3 click maximum ratings
Description
Min
Typ
Max
Unit
Operational Current Range (28V DC /
220V AC)
0
-
6
A
Operational Voltage Range (AC)
0
-
220
V
Operational Voltage Range (DC)
0
-
28
V
Mechanical Endurance
0
-
100,000
operations
Onboard settings and indicators
Label
Name
Default
Description
LD1
PWR
-
Power indicator LED
LD2
REL1
-
Relay 1 activity LED indicator
LD3
REL2
-
Relay 2 activity LED indicator
Software support
We provide a library for the Relay 3 Click on our LibStock page, as well as a
demo application (example), developed using MikroElektronika compilers. The
demo can run on all the main MikroElektronika development boards.
Library Description
The library contains functions for turning on/off relays 1 and 2. Library
contains functions for turning on/off relays 1 and 2 after a defined period of
time.
Key functions:
void relay3_relayOn( uint8_t relay_ ) - Turns selected relay on.
void relay3_relayOff( uint8_t relay_ ) - Turns selected relay off.
void relay3_onDelay( uint8_t relay_, uint8_t units_, uint16_t time_ ) - Turns selected
void relay3_offDelay( uint8_t relay_, uint8_t units_, uint16_t time_ ) - Turns selected
relay on after a defined period of time in selected units of time.
relay off after a defined period of time in selected units of time.
Examples description
The application is composed of three sections :
System Initialization - Initializes LOG functionality, initializes RST and CS pins as OUTPUTs.
Application Initialization - Initializes GPIO driver.
Application Task - Activates relays 1 and/or 2 based on user input.
void applicationTask( )
{
dataReady = UART_Rdy_Ptr( );
if (dataReady != 0)
{
receivedData = UART_Rd_Ptr( );
switch (receivedData)
{
case '1' :
{
relay3_case1( );
break;
}
case '2' :
{
relay3_case2( );
break;
}
case '3' :
{
relay3_case3( );
break;
}
default :
{
mikrobus_logWrite( "wrong command", _LOG_LINE );
break;
}
}
}
}
Additional Functions
void relay3_case1() - Turns relay 1 on/off
void relay3_case2() - Turns relay 2 on/off
void relay3_case3() - Turns relay 3 on/off
The full application code, and ready to use projects can be found on
our LibStock page.
Other mikroE Libraries used in the example:
UART
Additional notes and informations
Depending on the development board you are using, you may need USB UART
click, USB UART 2 click or RS232 click to connect to your PC, for development
systems with no UART to USB interface available on the board. The terminal
available in all MikroElektronika compilers, or any other terminal application
of your choice, can be used to read the message.
https://www.mikroe.com/relay‐3‐click/2‐13‐19