Arduino board, LDR, LABVIEW setup

1. EXPERIMENT – 4
OBJECTIVE: To measure the intensity of light using LDR sensor by calibrating voltage with
Lumens using equations in LabVIEW.
APPARATUS USED: Arduino board, LDR, LABVIEW setup.
THEORY:
Introduction to LABVIEW: LabVIEW is an integrated development environment designed
specifically for engineers and scientists. Native to LabVIEW is a graphical programming language
(G) that uses a dataflow model instead of sequential lines of text code, empowering you to write
functional code using a visual layout that resembles your thought process. This means you spend
less time worrying about semicolons and syntax and more time solving the problems that matter.
Introduction to Arduino: Arduino is an open-source electronics platform based on easy-to-use
hardware and software. Arduino boards are able to read inputs - light on a sensor, a finger on a button,
or a Twitter message - and turn it into an output - activating a motor, turning on an LED, publishing
something online. You can tell your board what to do by sending a set of instructions to the
microcontroller on the board. To do so you use the Arduino programming language (based on Wiring),
and the Arduino Software (IDE), based on Processing.

2. Over the years Arduino has been the brain of thousands of projects, from everyday objects to
complex scientific instruments. A worldwide community of makers - students, hobbyists, artists,
programmers, and professionals - has gathered around this open-source platform, their
contributions have added up to an incredible amount of accessible knowledge that can be of great
help to novices and experts alike.
Light Emitting Diode: LDR is a light-controlled variable resistor. The resistance of a photoresistor
decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A
photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated
switching circuits. A photoresistor is made of a high resistance semiconductor. In the dark, a
photoresistor can have a resistance as high as several megohms (MΩ), while in the light, a
photoresistor can have a resistance as low as a few hundred ohms. If incident light on a
photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give
bound electrons enough energy to jump into the conduction band. The resulting free electrons (and
their hole partners) conduct electricity, thereby lowering resistance. The resistance range and
sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique
photoresistor may react substantially differently to photons within certain wavelength bands.
Calculate light intensity:
The resistance of the Light Dependent Resistor (LDR) varies according to the amount of light that
falls on it. The relationship between the resistance RL and light intensity Lux for a typical LDR is
RL=500/Lux (1)
If the LDR connected to 5V through a 3.3K resistor, using the voltage divider rule, the output
voltage of the LDR is
Vo=5×RL/(RL+3.3) (2)
Substituting RL from equation 1 into equation 2, we obtain the light intensity

3. Lux= (2500*Vo−500)/3.3 (3)
For a low cost LDR, at the same light intensity, the part to part variation in resistance can be as
high as 50%. Therefore such a low cost LDR is seldom used for measuring light intensity but more
for light presence/absence detection.
Parameter Min Typ Max Unit Test Cond
RL Light Resistance 20 100 kΩ 10 lux
5 kΩ 100 lux
Table 1: Typical Low Cost LDR Specification
The LabVIEW VI that reads the voltage across the LDR and converts the voltage to lux is
called EMANT300 Example LDR.VI
Interface Arduino through LabVIEW:
Step 1: In LabVIEW (any version) establish the following front panel
Step 2: Establish the following block diagram.

4. Step 4: This virtual instrument:
>> Starts communication with Arduino.
>> Detects if there is a change in control knob value.
>> If there is a change it sends the new value to Arduino.
>> Else, it clears serial port Input/output register to avoid data overflow and serial port
overloading.
>> When pressing STOP, it sends “0” (brake or hold order) to Arduino.
Step 5: Arduino Code
(Attachment available)
Step 7: This Arduino Sketch:
Checks if LabVIEW sent a new value. If there is a new value, it converts it into integer byte with
the same value. This integer byte represents the delay interval used in stepping sequence. That,
the greater the delay the lower the speed and vice versa. Else, Arduino continue running the
motor at current speed. This prevents the processor from overloading the serial port and pushes it
to avoid Arduino Serial port hanging.
RESULT: Successfully measure the intensity of light using LDR sensor by calibrating voltage
with Lumens using equations in LabVIEW.