Wednesday, December 11, 2013

Basics of connecting HDF27 relay using

HFD27/005-S is a relay that is used commonly in many embedded circuits. In the post we will see the basics of using the HFD27 relay using the Arduino uno board.

A relay is used to connect or disconnect a circuit based on a trigger signal.

The following figure shows the wiring diagram for the HFD27.

 photo HFD27_witing.png

The pins 1 and 16 are the pins where we need to give the trigger pulse.

The pins 4,6,8 is one set of terminals which can be used to connect/disconnect a circuit and smilarly 13,11,9 are another set of terminals. Thus we have two relays in the HFD27 but both are controlled by the same trigger signal.

Among the three pins 4,6,8 4 and 6 are normally closed that is 4 is be default connected to 6 and when the triggering signal or pulse is given to pin1 the connection between 4 and 6 is broken.

Connection between 4 and 8 is normally open and when a signal/pulse is given to the pin1 4 and 8 get connected to each other.

Which means the arm of the switch is connected between 4 and 6 by default and when a pulse is given to the relay the arm moved from 6 to 8, thus disconnecting 6 and connecting 4 to 8.

The same it true for the pins 13,11 and 9 respectively.

To test its using Arduino make the following connections

Connect pin1 of HFD27 to digital I/O Pin4 of Arduino.
Connect pin 4 to 5v pin on Arduino board.
Connect pin 6 to a 1K resistor
Connect the other end of the resistor to a the anode of an LED,LED1.
Connect pin 13 also the 5v pin on Arduino board
Connect pin 9 to a 1k Resistor
Connec the other end of the resistor to the anode of an LED,LED2.
Connect pin 16 and cathode of the LEDs to a common point and connect the common point to the ground pin on the Arduino board.

In the circuit we are going to use send the trigger pulse to pin 4 of Arduino which will send the signal to the relay hence make/break the connections.

From the connections that we made above the LED1 will be on by default and LED2 will be off. To test it just connect the Arduino board with out laoding any program and the LED1 should turn and LED2 should be off.

Now load the following program into the board.

Once the program is loaded and run, we should see the LED1 and LED2 turn on and turn off alternately every 4 seconds as we are changing the state of the triggering signal every 4 seconds.

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