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Dual Relay Board Kit (#27114)
The Dual Relay Board can be used to turn lights, fans and other devices on/off while keeping them
isolated from your microcontroller. Once properly assembled, the Dual Relay Board Kit allows you to
control two high-power devices (up to 8 A) via the included Omron mechanical relays.
Independent
control of each relay is provided via a 2 x 3 header — friendly to servo cables and convenient connection
to many development boards, such as the Board of Education, Propeller Board of Education, Professional
Development Board and Propeller Professional Development Board. LEDs indicate relay status.
Features
Control two high-power devices at up to 8 A each with one kit
Provides isolation between microcontroller and device being controlled
Screw terminals for relay connections
3-pin servo-style headers for signal interface
LED indicators for each relay
Key Specifications
Power Requirements: 12 VDC @ 85 mA (nominal)
Communication Interface: Logic (3.3 V/5 V) High/Low
Operating temperature: -40 to +185 °F (-40 to +85 °C)
Dimensions: 2.3” L x 1.8” W x 0.7” H (58.4 x 45.8 x 1.8 cm)
Application Ideas
120 VAC brushless lighting/fan control
12 VDC automotive applications
Copyright © Parallax Inc.
Dual Relay Board Kit (#27114)
v1.0 5/9/2012 Page 1 of 7
Bill of Materials
Designator Description
J1-J4
J5
K1-K2
R1-R4
D1-D2
D3-D4
Q1-Q2
PCB1
2 Position Screw Terminal Block
Connector, Header, 2x3, 0.1", Straight
Omron Relay G2RL-14-DC12, SPDT, 12A, 12VDC
Resistor, 1K, 5%, 1/4W, CF
LED, Red, T1-3/4
1N4004 Diode, Rectifier, 1V, 400V, 1A, Axial
2N3904 NPN Transistor, TO-92
Raw PCB, Dual Relay Board
Quantity
4
1
2
4
2
2
2
1
Part #
452-00012
450-00105
400-00052
150-01020
350-00006
501-00006
500-00008
300-27114
Additional Items Required
Soldering iron
Solder
Diagonal cutters
Safety glasses
Assembly Instructions
Step 1
Install the lower profile components first (D1-D2,
D3-D4, R1-R4 and Q1-Q2).
When installing D1-D2 (Red LED), be sure the flat
side of the LED lines up with the flat side on the
silkscreen.
When installing D3-D4 (1N4004 Diode), be sure the
stripe lines up with the stripe on the silkscreen.
When installing Q1-Q2 (2N3904 NPN Transistor),
be sure the flat face lines up with the flat side on
the silkscreen.
Resistors R1-R4 are not polarized and can be
mounted in either direction, however you will have
to bend one lead over to install the resistors
upright. See the photo at right for details.
Copyright © Parallax Inc.
Dual Relay Board Kit (#27114)
v1.0 5/9/2012 Page 2 of 7
Step 2
Install the connectors next (J1-J3, J4 and J5).
When installing J1-J3 (green terminal blocks), be
sure to connect these three together by sliding
them into each other using the tab/groove
before
installing onto the PCB. Wire holes should be facing
the outside of the PCB.
J5 (remaining green terminal block) is by itself at
the opposite end of the board. Wire holes should
be facing the outside of the PCB.
J4 should be installed with the shorter end of the
pins being inserted into the PCB.
See the photo at right for details.
Step 3
Install the relays last (K1-K2).
Be sure the relays are fully seated into the holes
before you begin soldering.
See the photo at right for details.
Copyright © Parallax Inc.
Dual Relay Board Kit (#27114)
v1.0 5/9/2012 Page 3 of 7
Precautions
As with any device capable of switching high voltages, precautions should always be taken to avoid
damage and/or injury. The following precautions are recommended in addition to any precautions by the
manufacturer of any equipment connected to this device.
Always disconnect main power when connecting circuits to the Dual Relay Board.
Download and read the relay datasheet from the 27114 product page before using the relays.
When using with high-power circuits, mount the Dual Relay Board inside a suitable enclosure or
electrical panel using standoffs. The board should not be able to move.
Secure all electrical connections to the board so they cannot move; provide strain relief for any
wires extending outside the enclosure.
Fuse any incoming voltage rails that are to be switched by the relays, prior to entering the Dual
Relay Board.
Always be sure any incoming voltage rails are powered off prior to connecting them to the Dual
Relay Board.
Observe Max Switching Current listed below! The Relays are capable of switching more current
than the Terminal Blocks and PCB can handle.
While mechanical relays provide physical electrical isolation from control circuits, it is possible for
EMF generated by high-power devices to affect the control circuits. This is especially true if the
control wires and/or power leads are longer than 6”. Always try to keep wires as short as possible
and avoid running high-power leads near or across control lines.
Pin Definitions and Ratings (J4)
Pin
1
2
3
4
5
6
Name
Relay 1
Relay 2
NC
NC
GND
GND
Type
I
I
―
―
G
G
Function
Relay 1 Signal Input (3.3V/5V)*
Relay 2 Signal Input (3.3V/5V)*
No Connection
No Connection
Signal/Relay Coil Ground
Signal/Relay Coil Ground
Pin Type: P = Power, G = Ground, I = Input, O = Output
*Inputs signals on pin 1 and 2 are typically 3.3 V or 5 V but are independent and do not need to be the
same. For example Relay 1 could be switched via a 3.3 V control signal while Relay 2 could be switched
via a 5 V control signal.
Specifications
Symbol
12V
―
―
Quantity
Relay Supply Voltage
Relay Supply Current
Max Switching Current
Minimum
7
―
―
Typical
12
85
―
Maximum
―
―
8
Units
V
mA
A
Copyright © Parallax Inc.
Dual Relay Board Kit (#27114)
v1.0 5/9/2012 Page 4 of 7
Module Dimensions / Connection Diagram
Note: The two pins at the J4 (pins 5/6) label are both ground pins, while the pins labeled RLY1 and RLY2
(pins 1/2) are the signal/control pins. Pins 3 and 4 are no connected but allowed you to connect a
powered servo cable without a conflict with the servo supply.
Theory of Operation
In the schematic details to the right the
red box is intended to encapsulate one
complete relay circuit to help show how
the relay driver circuit is built and what
components are required.
One complete relay circuit consists of ½
of J4, R3, Q1, D1, R1, D3 and K1. J5
supplies voltage to K1 at port 12 V. The
relay (K1) requires approximately 33 mA
to activate. This is more than most I/O
pins on a microcontroller can source/sink,
so a transistor (Q1) is used to drive the
relay.
Q1 is a standard NPN switching/amplifier
transistor with a usable current rating of
100 mA, which is well within the
requirements for the relay (~33 mA) and
LED (~10 mA). The gain (h
FE
) of this
transistor may vary but is typically 100,
while the minimum is 30. The V
BE
(forward voltage) of Q1 is about 0.7 V, so
to allow a range of control voltages the
resistor (R3) must be chosen carefully.
Copyright © Parallax Inc.
Dual Relay Board Kit (#27114)
v1.0 5/9/2012 Page 5 of 7
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