Chapter 2.doc

CHAPTER 3
HARDWARE REQUIREMENTS
3.1 Node MCU:
Overview:
ESP-12E Wi-Fi module is developed by Ai-thinker Team. core processor
ESP8266 in smaller sizes of the module encapsulates Tensilica L106 integrates
industry-leading ultra low power 32-bit MCU micro, with the 16-bit short mode,
Clock speed support 80 MHz, 160 MHz, supports the RTOS, integrated Wi-Fi
MAC/BB/RF/PA/LNA, on-board antenna. The module supports standard
IEEE802.11 b/g/n agreement, complete TCP/IP protocol stack. Users can use the
add modules to an existing device networking, or building a separate network
controller. ESP8266 is high integration wireless SOCs, designed for space and
power constrained mobile platform designers. It provides unsurpassed ability to
embed Wi-Fi capabilities within other systems, or to function as a standalone
application, with the lowest cost, and minimal space requirement.
ESP8266EX offers a complete and self-contained Wi-Fi networking
solution; it can be used to host the application or to offload Wi-Fi networking
functions from another application processor. When ESP8266EX hosts the
application, it boots up directly from an external flash.
ESP8266EX is among the most integrated Wi-Fi chip in the industry; it
integrates the antenna switches, RF balun, power amplifier, low noise receive
amplifier, filters, power management modules, it requires minimal external
circuitry, and the entire solution, including front-end module, is designed to
occupy minimal PCB area.

Figure:ESP8266-12E
The ESP8266 has seen a wide adoption as a cost-effective solution for IOT and
Wi-Fi-capable devices. The ESP8266 was developed by Shangai-based Espressif
systems, as a Serial (UART) to Wi-Fi SoC (System on a Chip) based around
a Tensilica Xtensa LX3DPU. This tiny IC includes an RF front end, RAM, and
(usually) an onboard TCP/IP stack that allows it ready to connect to a nearby
Access Point, to act as an Access Point itself, or both.
Family of Breakout Boards (ESP-NN):
Quickly after launch, a variety of breakout boards for
the ESP8266 started becoming available. The most popular ones have been
the ESP-NN series, which typically integrate the SOC along with Flash RAM, a
crystal, and even an onboard antenna. The most salient distinction between
different ESP-NN models are the pins that are broken out from the ESP8266
As the ESP8266 was developed as a Serial to Wi-Fi adapter, its firmware
implemented an interpreter for AT commands. Thus initial usage of the IC was
limited to using a either a USB to Serial adapter, or a separate microcontroller
(e.g., ATmega328) to issue AT commands over the ESP8266's Serial UART

interface. For this reason, the ESP-01 board quickly became popular amongst
the ESP8266 community because of its 2×4, 0.1in-pitch connector that can be
easily wired to a USB to Serial adapter.
The connector gave access to the pins used for serial communication,
namely RX and TX, as well as 4 control
pins, GPIO0, GPIO2, CH_PD and RST (reset), along with VCC and GND.
However, other ESP-NN boards offer access to a wider variety of pins,
although their packaging is of a custom Surface-Mount Device, with castellated
pins as seen in the documentation page linked above. From the different ESP-NN
boards, we began to experiment with the ESP-12E. The main reason is that this
module was the one chosen by the developers of the Node MCU project for their
hardware Dev Kit 1.0
Because the ESP8266 provides a cost-effective solution to the rapidly
growing market of internet-connected projects and devices (i.e., the so-called
Internet of Things), it has become one of the most popular development platforms
over the past year and a half. In consequence, a dedicated community has formed
around the platform which has been focused on improving its functionality.
For starters, different firmware options have been ported to run on
the ESP8266, effectively taking it from a simple Serial to Wi-Fi adapter into a
fully functional microcontroller with access to its GPIO and hardware-based
functions like PWM, I2C, 1-Wire communication, and ADC; all this, of course, in
addition to maintaining its Wi-Fi capabilities.
Features:
• 802.11 b/g/n
• Integrated low power 32-bit MCU
•Integrated 10-bit ADC
• Integrated TCP/IP protocol stack
• Integrated TR switch, balun, LNA, power amplifier and matching network
• Integrated PLL, regulators, and power management units
• Supports antenna diversity
• Wi-Fi 2.4 GHz, support WPA/WPA2

• Support STA/AP/STA+AP operation modes
• Support Smart Link Function for both Android and IOS devices
• Support Smart Link Function for both Android and iOS devices
• SDIO 2.0, (H) SPI, UART, I2C, I2S, IRDA, PWM, GPIO
• STBC, 1x1 MIMO, 2x1 MIMO
• A-MPDU & A-MSDU aggregation and 0.4s guard interval Shenzhen Anxinke
Technology
• Deep sleep power < 5uA
• Wake up and transmit packets in < 2ms
• Standby power consumption of < 1.0mW (DTIM3)
• +20dBm output power in 802.11b mode • Operating temperature range -40C ~
125C
Applications:
 Smart power plugs
 Home automation
 Mesh network
 Industrial wireless control
 Baby monitors
 IP Cameras
 Sensor networks
 Wi-Fi location-aware devices
 Security ID tags
 Wi-Fi position system beacons
AT Commands:
Command Description
AT Test AT start up
AT+RST Restart module
AT+GMR View version Info
AT+GSLP Enter deep sleep mode
ATE AT commands echo or not

AT+RESTORE Factory Reset
AT+UART UART Configuration
AT+UART_CUR UART current configuration
AT+UART_DEF UART default configuration, save to flash
AT+SLEEP Sleep mode
AT+RFPOWER Set maximum value of RF TX power
AT+RFVVD RF TX power according to VDD33
A few different firmware options are available for the ESP8266. These allow us to
access the module in different ways, as you can see below.
AT Command Processor(Default):
The quickest way to get started with the ESP8266 is to use its original firmware,
which allows it to process any AT commands that it receives over its Serial
UART interface. The biggest advantage of this option is that we need not be
familiar with any specific language or framework to use the module. We can
simply send it a series of commands to achieve our goal. The downside to this is
that we need either an additional microcontroller involved or a USB to Serial
adapter to send the necessary commands.
Whereas the AT commands are the standard way of communicating with
wireless-capable ICs (e.g., Bluetooth, Wi-Fi, GSM), they pose the limitation of
needing another module to run the application that specifies these commands
accordingly. However, if we could run the application within the ESP8266 itself
then we'd have everything self-contained by a single IC. Fortunately, Espressif
made a Software Development Kit (SDK) available that allowed users to flash
different firmware options.
ESP-12E Pindesign:

Pin Descriptions:
NO. Pin Name Function
1 RST Reset the module
2 ADC A/D Conversion result. Input voltage range 0-
1v,scope:0-1024
3 EN Chip enable pin. Active high
4 IO16 GPIO16; can be used to wake up the chipset from de
sleep mode.
5 IO14 GPIO14; HSPI_CLK
6 IO12 GPIO12; HSPI_MISO

7 IO13 GPIO13; HSPI_MOSI; UART0_CTS
8 VCC 3.3V power supply (VDD)
9 CS0 Chip selection
10 MISO Salve output Main input
11 IO9 GPIO9
12 IO10 GBIO10
13 MOSI Main output slave input
14 SCLK Clock
15 GND GND
16 IO15 GPIO15; MTDO; HSPICS; UART0_RTS
17 IO2 GPIO2; UART1_TXD
18 IO0 GPIO0
19 IO4 GPIO4
20 IO5 GPIO5
21 RXD UART0_RXD; GPIO3
22 TXD UART0_TXD; GPIO1
Table: Pin mode
Mode GPIO15 GPIO0 GPIO2
UART Low Low High
Flash Boot Low High High
Table: Dimensionof ESP-12EWi-FiModule
Length Width Height PAD
Size(Bottom)
Pin Pitch
16 mm 24mm 3 mm 0.9 mm x 1.7 mm 2mm
Functional Descriptions:
MCU:
ESP8266EX is embedded with Tensilica L106 32-bit micro controller (MCU),
which features extra low power consumption and 16-bit RSIC. The CPU clock
speed is 80MHz. It can also reach a maximum value of 160MHz. ESP8266EX is

often integrated with external sensors and other specific devices through its
GPIOs; codes for such applications are provided in examples in the SDK.
Memory Organization:
Internal SRAM and ROM:
ESP8266EX Wi-Fi SOC is embedded with memory controller, including SRAM
and ROM. MCU can visit the memory units through iBus, dBus, and AHB
interfaces. All memory units can be visited upon request, while a memory arbiter
will decide the running sequence according to the time when these requests are
received by the processor. According to our current version of SDK provided,
SRAM space that is available to users is assigned as below:
▪ RAM size < 36kB, that is to say, when ESP8266EX is working under the
station mode and is connected to the router, programmable space accessible to
user in heap and data section is around 36kB.)
▪ There is no programmable ROM in the SOC, therefore, user program must be
stored in an external SPI flash.
External SPI Flash:
This module is mounted with an 4 MB external SPI flash to store user programs.
If larger definable storage space is required, a SPI flash with larger memory size
is preferred. Theoretically speaking, up to 16 MB memory capacity can be
supported.
3.2 Powersupply

All digital circuits require regulated power supply. In this article we
are going to learn how to get a regulated positive supply from the mains supply.
Step Down Transformer:
A transformer consists of two coils also called as “WINDINGS”
namely PRIMARY & SECONDARY. They are linked together through
inductively coupled electrical conductors also called as CORE.
A changing current in the primary causes a change in the Magnetic Field in
the core & this in turn induces an alternating voltage in the secondary coil. If load
is applied to the secondary then an alternating current will flow through the load.
If we consider an ideal condition then all the energy from the primary circuit will
be transferred to the secondary circuit through the magnetic field.
So,
The secondary voltage of the transformer depends on the number of turns in
the Primary as well as in the secondary.

Fig 3.4: Transformer
Rectifier:
A rectifier is a device that converts an AC signal into DC signal. For rectification
purpose we use a diode, a diode is a device that allows current to pass only in one
direction i.e. when the anode of the diode is positive with respect to the cathode
also called as forward biased condition & blocks current in the reversed biased
condition.
Rectifier can be classified as follows:
Half Wave rectifier.
Full Wave rectifier
Bridge rectifier
Filter Capacitor:
Even though half wave & full wave rectifier give DC output, none of them
provides a constant output voltage. For this we require to smoothen the waveform
received from the rectifier. This can be done by using a capacitor at the output of
the rectifier this capacitor is also called as “FILTER CAPACITOR” or
“SMOOTHING CAPACITOR” or “RESERVOIR CAPACITOR”. Even after
using this capacitor a small amount of ripple will remain.
We place the Filter Capacitor at the output of the rectifier the capacitor will
charge to the peak voltage during each half cycle then will discharge its stored
energy slowly through the load while the rectified voltage drops to zero, thus
trying to keep the voltage as constant as possible.
If we go on increasing the value of the filter capacitor then the Ripple will
decrease. But then the costing will increase. The value of the Filter capacitor
depends on the current consumed by the circuit, the frequency of the waveform &
the accepted ripple.

Where,
Vr= accepted ripple voltage.( should not be more than 10% of the voltage)
I= current consumed by the circuit in Amperes.
F= frequency of the waveform. A half wave rectifier has only one peak in one
cycle so F=25HZ
Whereas a full wave rectifier has Two peaks in one cycle so F=100hz.
Fig 2.5 : Waveforms of Filter capacitor
Voltage Regulator:
A Voltage regulator is a device which converts varying input voltage into a
constant regulated output voltage.
A regulated power supply is very much essential for several electronic devices
due to the semiconductor material employed in them have a fixed rate of current
as well as voltage. The device may get damaged if there is any deviation from the
fixed rate.
Here comes the 7805 Voltage Regulator IC to the rescue. It is an IC in the 78XX
family of linear voltage regulators that produce a regulated 5V as output.
7805 Voltage Regulator:
7805 is a three terminal linear voltage regulator IC with a fixed output voltage of
5V which is useful in a wide range of applications.
Some of the important features of the 7805 IC are as follows:

It can deliver up to 1.5 A of current (with heat sink).
Has both internal current limiting and thermal shutdown features.
Requires very minimum external components to fully function.
Fig 2.6: Voltage Regulator
Pin description of IC 7805 regulator:
As mentioned earlier, 7805 is a three terminal device with the three pins being 1.
INPUT, 2. GROUND and 3.OUTPUT. The following image shows the pins on a
typical 7805 IC in To-220 Package.
Pin no Pin Description
1 INPUT Pin 1 is the INPUT Pin. A
positive unregulated voltage
is given as input to this pin.
2 GROUND Pin 2 is the GROUND Pin.
It is common to both Input
and Output.
3 OUTPUT Pin 3 is the OUTPUT Pin.
The output regulated 5V is
taken at this pin of the IC.

Table 1: Pin description of IC 7805
Features:
 The first important point to note is that the input voltage should always be
greater than the output voltage (atleast by 2.5V).
 The input current and output current are almost identical. This means that
when a 7.5V 1A supply is given at input, the output will be 5V 1A.
 The remaining power is dissipated as heat and hence a heat sink like the
one shown below must be used with 7805 IC.
3.3 DHT-11 Sensor:
Over View:
Sensing and controlling current flow is a fundamental requirement in a wide
variety of applications including, over-current protection circuits, battery
chargers, switching mode power supplies, digital watt meters, programmable
current sources, etc. One of the simplest techniques of sensing current is to place a
small value resistance (also known as Shunt resistor) in between the load and the
ground and measure the voltage drop across it, which in fact, is proportional to the
current flowing through it. Whereas this technique is easy and straightforward to
implement, it may not be very precise because the value of the shunt resistor
slightly varies with its temperature, which in fact is not constant because of the
Joule heating. Besides, this simple technique does not provide isolation between
the load and current sensing unit, which is desirable in applications involving high
voltage loads. Today, we will talk about Allegro ACS712 device which provides
an economical and precise way of sensing AC and DC currents based on Hall-
effect. This discussion is divided into two parts. The first part will provide a brief
overview of the ACS712 sensor and its characteristics. In the second part, a test
experiment will be carried out to interface the sensor with a PIC microcontroller
to measure a dc current.

Fig: ACS712-05 Current sensor Module
Description:
The current sensing technique based on a shunt resistor is described in How to
measure dc current with a microcontroller? And implemented in the Multi-
functional power supply project. The major disadvantages of this technique are:
 load is lifted from the direct ground connection.
 non-linearity in the response due to Joule heating that drifts the resistance
value.
 lack of electrical isolation between the load and the sensing part.
The Allegro ACS712 current sensor is based on the principle of Hall-effect,
which was discovered by Dr. Edwin Hall in 1879. According to this principle,
when a current carrying conductor is placed into a magnetic field, a voltage is
generated across its edges perpendicular to the directions of both the current and
the magnetic field. It is illustrated in the figure shown below. A thin sheet of

semiconductor material (called Hall element) is carrying a current (I) and is
placed into a magnetic field (B) which is perpendicular to the direction of current
flow. Due to the presence of Lorentz force, the distribution of current is no more
uniform across the Hall element and therefore a potential difference is created
across its edges perpendicular to the directions of both the current and the field.
This voltage is known Hall voltage and its typical value is in the order of few
microvolts. The Hall voltage is directly proportional to the magnitudes of I and B.
So if one of them (I and B) is known, then the observed Hall voltage can be used
to estimate the other.
The ACS712 device is provided in a small, surface mount SOIC8 package. It
consists of a precise, low-offset, linear Hall sensor circuit with a copper
conduction path located near the surface of the die. When current is applied
through the copper conductor, a magnetic field is generated which is sensed by
the built-in Hall element. The strength of the magnetic field is proportional to the
magnitude of the current through the conduction path, providing a linear
relationship between the output Hall voltage and input conduction current. The
on-chip signal conditioner and filter circuit stabilizes and enhances the induced
Hall voltage to an appropriate level so that it could be measured through an ADC
channel of a microcontroller. The pin diagram of ACS712 device and its typical

application circuit is shown below. Pins 1, 2 and 3, 4 form the copper conduction
path which is used for current sensing.
The internal resistance of this path is around 1.2 m? Thus providing low power
loss. As the terminals of this conduction path are electrically isolated from the
sensor leads (pins 5 through 8), the ACS712 device eliminates the risk of
damaging the current monitoring circuit due to the high voltage on the conduction
side. The electrical isolation between the conduction current and the sensor circuit
also minimizes the safety concerns while dealing with high voltage systems.
Fig: Pin diagram and a typical application circuit of ACS712
In low-frequency applications, it is often desirable to add a simple RC filter
circuit at the output of the device to improve the signal-to-noise ratio. The
ACS712 contains an internal resistor (RF) connected between the the output of the
on-chip signal amplifier and the input of the output buffer stage (shown below).
The other end of the resistor is externally accessible through pin 6 (Filter). With

this architecture, users can implement a simple RC filter through the addition of
an external capacitor (CF) between the Filter pin and ground. It should be noted
that the use of external capacitor increases the rise time of the sensor output, and
therefore, sets the bandwidth of the input signal. The maximum bandwidth of the
input signal is 80 KHz at zero external filter capacitor. The bandwidth decreases
with increasing CF. The datasheet of ACS712 recommends using 1 nF for CF to
reduce noise under nominal conditions.
Fig: Functional block diagram of ACS712
Sensitivity and output of ACS712:
The output of the device has positive slope when an increasing current flows
through the copper conduction path (from pins 1 and 2, to pins 3 and 4). The
ACS712 device comes in three variants, providing current range of±5A (ACS712-
05B), ±20A (ACS712-20B), and ±30A (ACS712-30A). The ACS712-05B can
measure current up to ±5A and provides output sensitivity of 185mV/A (at +5V
power supply), which means for every 1A increase in the current through the
conduction terminals in positive direction, the output voltage also rises by 185
mV. The sensitivities of 20A and 30A versions are 100 mV/A and 66 mV/A,

respectively. At zero current, the output voltage is half of the supply voltage
(Vcc/2). It should be noted that the ACS712 provides ratio metric output, which
means the zero current output and the device sensitivity are both proportional to
the supply voltage, VCC. This feature is particularly useful when using the
ACS712 with an analog-to-digital converter.
The precision of any A/D conversion depends upon the stability of the reference
voltage used in the ADC operation. In most microcontroller circuits, the reference
voltage for A/D conversion is the supply voltage itself. So, if the supply voltage is
not stable, the ADC measurements may not be precise and accurate. However, if
the reference voltage of ADC is same as the supply voltage of ACS712, then the
ratio metric output of ACS712 will compensate for any error in the A/D
conversion due to the fluctuation in the reference voltage.
Let me explain this with an example. Suppose, an ADC chip uses Vcc = 5.0V as a
reference for A/D conversion and the same supply voltage powers an ACS712
sensor chip. The analog output of the ACS712 will be digitized through the ADC
chip. When there is zero current through the current sensor, the output is Vcc/2 =
2.5V. If the ADC chip is 10-bit (0-1023), it will convert the analog output from
the ACS712 sensor into digital value of 512 count. Now, if the supply voltage
drifts and becomes Vcc = 4.5V, then, due to the ratio metric nature, the new
output of the ACS712 sensor will be 4.5/2 = 2.25V, which will still be digitized to
512 by the ADC as its reference voltage is also lowered to 4.5V. Similarly, the
sensitivity value will also be lowered by a factor of 4.5/5 = 0.9, which means if
the ACS712-05B is powered with a 4.5V supply, the sensitivity is reduced to
166.5 mV/A, instead of 185mV, A. This concludes that any fluctuation in the
reference voltage will not be a source of error in the analog-to-digital conversion
of the ACS712 output signals.
The curve below shows the nominal sensitivity and transfer characteristics of the
ACS712-05B sensor powered with a 5.0V supply. The drift in the output is

minimum for a varying operating temperature, which is attributed to an innovative
chopper stabilization technique implemented on the chip (read ACS712 datasheet
for detail).
Accurate sensor to measure AC/DC current up to 20A. The sensor can even
measure high AC mains current and is still isolated from the measuring part due
to integrated hall sensor. The board operates on 5V.
ACS712 current sensor operates from 5V and outputs analog voltage proportional
to current measured on the sensing terminals. You can simple use a
microcontroller ADC to read the values.

Sensing terminal can even measure current for loads operating at high voltages
like 230V AC mains while output sensed voltage is isolated from measuring part.

Provides up to 3000 VRMS galvanic isolation. The low-profile, small form factor
packages are ideal for reducing PCB area over sense resistor op-amp or bulky
current transformer configurations. The low resistance internal conductor allows
for sensing up to 20 A continuous current. Providing typical output error of 1%.
Features:
 100 mV/A output sensitivity
 5.0 V, single supply operation
 Output voltage proportional to AC or DC currents
 Factory-trimmed for accuracy
 Extremely stable output offset voltage
 Nearly zero magnetic hysteresis
 Ratio metric output from supply voltage
 Low-noise analog signal path
 Device bandwidth is set via the new FILTER pin
 5 µs output rise time in response to step input current
 80 kHz bandwidth
 Total output error 1.5% at TA = 25°C
 Small footprint, low-profile SOIC8 package
 1.2 mΩ internal conductor resistance
 2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8
Sensor Specifications:

3.4 Relay:
Introduction:
A relay is an electrically operated switch. Many relays use an electromagnet to
mechanically operate a switch, but other operating principles are also used, such as solid-
state relays. Relays are used where it is necessary to control a circuit by a separate low-
power signal, or where several circuits must be controlled by one signal. The first relays
were used in long distance telegraph circuits as amplifiers: they repeated the signal
coming in from one circuit and re-transmitted it on another circuit. Relays were used
extensively in telephone exchanges and early computers to perform logical operations.
A type of relay that can handle the high power required to directly control an electric
motor or other loads is called a contactor. Solid-state relays control power circuits with
no moving parts, instead using a semiconductor device to perform switching. Relays with
calibrated operating characteristics and sometimes multiple operating coils are used to
protect electrical circuits from overload or faults; in modern electric power systems these
functions are performed by digital instruments still called "protective relays".
Magnetic latching relays require one pulse of coil power to move their contacts in one
direction, and another, redirected pulse to move them back. Repeated pulses from the
same input have no effect. Magnetic latching relays are useful in applications where
interrupted power should not be able to transition the contacts.

Magnetic latching relays can have either single or dual coils. On a single coil device, the
relay will operate in one direction when power is applied with one polarity, and will reset
when the polarity is reversed. On a dual coil device, when polarized voltage is applied to
the reset coil the contacts will transition. AC controlled magnetic latch relays have single
coils that employ steering diodes to differentiate between operate and reset commands.
Basic design and operation:
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron
core (a solenoid), an iron yoke which provides a low reluctance path for magnetic flux, a
movable iron armature, and one or more sets of contacts (there are two contacts in the
relay pictured). The armature is hinged to the yoke and mechanically linked to one or
more sets of moving contacts. The armature is held in place by a spring so that when the
relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of
the two sets of contacts in the relay pictured is closed, and the other set is open. Other
relays may have more or fewer sets of contacts depending on their function. The relay in
the picture also has a wire connecting the armature to the yoke. This ensures continuity of
the circuit between the moving contacts on the armature, and the circuit track on
the printed circuit board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that
activates the armature and the consequent movement of the movable contact either makes
or breaks (depending upon construction) a connection with a fixed contact. If the set of
contacts was closed when the relay was de-energized, then the movement opens the
contacts and breaks the connection, and vice versa if the contacts were open. When the
current to the coil is switched off, the armature is returned by a force, approximately half
as strong as the magnetic force, to its relaxed position. Usually this force is provided by a
spring, but gravity is also used commonly in industrial motor starters. Most relays are
manufactured to operate quickly. In a low-voltage application this reduces noise; in a
high voltage or current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil to
dissipate the energy from the collapsing magnetic field at deactivation, which would
otherwise generate a voltage spike dangerous to semiconductor circuit components. Such
diodes were not widely used before the application of transistors as relay drivers, but
soon became ubiquitous as early germanium transistors were easily destroyed by this
surge. Some automotive relays include a diode inside the relay case.

Simple electromechanical relay
Applications of Relays:
Relays are used in electronics to switch a smaller current which in turn will control larger
current. They prevent the user to have direct contact to the main device being controlled
that might be holding high voltage. These devices are comparable to a remote control
which is used to make a big electronic equipment work. The larger relays or contactors
are being utilized in industries to provide energy on machineries such as pumps and
motors.
The function of relay can be easily understood by explaining how head lights turn on.
The switches to turn this on can be found on the dashboards of cars. Once moved, they
will send a small current on the coil turning on the contactor. The relay then will control a
high power load which in this case is the head lights. Besides this instance, relays have
other more applications which we deal with everyday but have not been able to notice.

Relays are being applied at home, industries and even on the street. Electronic equipment
for domestic use have parts that require energy in order to function. An example of it is
refrigerator. This appliance has motors and fans. Relays are responsible in controlling
these parts so that refrigerator work and produce cold temperature. Another application of
relays is controlling traffic lights. They can be operated remotely with the use of a
switching component. Automatic garage door is another occasion where relays are being
utilized. The door’s movement and direction are the ones being controlled.
Relays do not only energize electronic equipment but also make devices to stop
functioning. These capabilities have brought automation and convenience in our lives.
They let electronics run smoothly and safely. Now, we do not have to deal directly with
electronics that contain high voltage which may cause danger if they suddenly
malfunction.
2-Channel Relay Board:
This is a LOW Level 5V 2-channel relay interface board, and each channel needs
a 15-20mA driver current. It can be used to control various appliances and
equipment with large current. It is equipped with high-current relays that work
under AC250V 10A or DC30V 10A. It has a standard interface that can be
controlled directly by microcontroller. This module is optically isolated from high
voltage side for safety requirement and also prevent ground loop when interface
to microcontroller.

 Relay Maximum output: DC 30V/10A, AC 250V/10A.
 2 Channel Relay Module with Opto-coupler. LOW Level Trigger expansion
board, which is compatible with Arduino control board.
 Standard interface that can be controlled directly by microcontroller ( 8051,
AVR, *PIC, DSP, ARM, ARM, MSP430, TTL logic).
 Relay of high quality low noise relays SPDT. A common terminal, a normally
open, one normally closed terminal.
 Opto-Coupler isolation, for high voltage safety and prevent ground loop with
microcontroller.
Schematic:
VCC and RY-VCC are also the power supply of the relay module. When you
need to drive a large power load, you can take the jumper cap off and connect an
extra power to RY-VCC to supply the relay; connect VCC to 5V of the MCU
board to supply input signals. NOTES: If you want complete optical isolation,

connect "Vcc" to Arduino +5 volts but do NOT connect Arduino Ground.
Remove the Vcc to JD-Vcc jumper. Connect a separate +5 supply to "JD-Vcc"
and board Gnd. This will supply power to the transistor drivers and relay coils. If
relay isolation is enough for your application, connect Arduino +5 and Gnd, and
leave Vcc to JD-Vcc jumper in place.
It is sometimes possible to use this relay boards with 3.3V signals, if the JD-VCC
(Relay Power) is provided from a +5V supply and the VCC to JD-VCC jumper is
removed. That 5V relay supply could be totally isolated from the 3.3V device, or
have a common ground if opto-isolation is not needed. If used with isolated 3.3V
signals, VCC (To the input of the opto-isolator, next to the IN pins) should be
connected to the 3.3V device's +3.3V supply.
NOTE: Some Raspberry-Pi users have found that some relays are reliable and
others do not actuate sometimes. It may be necessary to change the value of R1
from 1000 ohms to something like 220 ohms, or supply +5V to the VCC
connection.

Module Layout:
Operating Principal:
See the picture below: A is an electromagnet, B armature, C spring, D moving
contact, and E fixed contacts. There are two fixed contacts, a normally closed one
and a normally open one. When the coil is not energized, the normally open
contact is the one that is off, while the normally closed one is the other that is on.

Supply voltage to the coil and some currents will pass through the coil thus
generating the electromagnetic effect. So the armature overcomes the tension of
the spring and is attracted to the core, thus closing the moving contact of the
armature and the normally open (NO) contact or you may say releasing the former
and the normally closed (NC) contact. After the coil is de-energized, the
electromagnetic force disappears and the armature moves back to the original
position, releasing the moving contact and normally closed contact. The closing
and releasing of the contacts results in power on and off of the circuit.
Input:
VCC : Connected to positive supply voltage (supply power according to relay
voltage)
GND : Connected to supply ground.
IN1: Signal triggering terminal 1 of relay module
IN2: Signal triggering terminal 2 of relay module
Output:
Each module of the relay has one NC (normally close), one NO (normally open)
and one COM (Common) terminal. So there are 2 NC, 2 NO and 2 COM of the
channel relay in total. NC stands for the normal close port contact and the state
without power. NO stands for the normal open port contact and the state with

power. COM means the common port. You can choose NC port or NO port
according to whether power or not.
Testing set up:
When a low level is supplied to signal terminal of the 2-channel relay, the LED at
the output terminal will light up. Otherwise, it will turn off. If a periodic high and
low level is supplied to the signal terminal, you can see the LED will cycle
between on and off.

Features:
The 2-Channel Relay Module includes the following features:
2.2.5 Incandescent:
Overview
The incandescent light bulb or lamp is a source of electric light that works by
incandescence, which is the emission of light caused by heating the filament.
They are made in an extremely wide range of sizes, wattages, and voltages.

Incandescent bulbs are the original form of electric lighting and have been in use
for over 100 years. While Thomas Edison is widely considered to be the
inventor of the incandescent bulb.
Working:
An incandescent bulb typically consists of a glass enclosure containing a
tungsten filament. An electric current passes through the filament, heating it to a
temperature that produces light.
Incandescent light bulbs usually contain a stem or glass mount attached to the
bulb's base which allows the electrical contacts to run through the envelope
without gas/air leaks. Small wires embedded in the stem support the filament
and/or its lead wires.
The enclosing glass enclosure contains either a vacuum or an inert gas to
preserve and protect the filament from evaporating.
Fig 2.10: Incandescent Bulb
Where are they used?
Incandescent bulbs require no external regulating equipment, have a very low
manufacturing cost, and work well on either alternating current or direct current.

They are also compatible with control devices such as dimmers, timers, and
photo sensors, and can be used both indoors and outdoors. As a result, the
incandescent lamp is widely used both in household and commercial lighting,
for portable lighting such as table lamps, car headlamps, and flashlights, and for
decorative and advertising lighting.

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