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ArduSensor Light Quickstart Guide

The Basics:


A light sensor, LDR (light-dependent resistor), or a photoresistor is a type of resistor that changes resistance depending on the amount of light it is exposed to.  A photoresistor makes a great light detector (for if the room is dark, or light).






First off, if you don’t know how to solder, go here to learn the basics so that you are thoroughly prepared to assemble your kit.


Parts in Kit:



Qtechknow ArduSensor Light PCB (Printed Circuit Board)

Mini Photoresistor

10K Ohm Resistor - 1/4W

Male Headers (5)


Tools Needed to Assemble:


Soldering Iron

Lead Free Solder

Safety Glasses

Safety Mask

Vise or Third Hand


You will need to get on your own:



Arduino Leonardo with micro-B USB Cable




Arduino Uno with USB-B Cable



When using lead, take precautions like:


  • Make sure to wash your hands with soap and water twice after you solder
  • Don’t eat the solder
  • Don’t touch your face or eyes after touching the solder
  • Wear a mask to prevent the solder smoke to come into your mouth, or to prevent you from inhaling it
  • When working with hot solder, you especially want to wear eye protection


Assembling the Kit:


Take out the ArduSensor Light PCB out of the the bag and put face up into a vice or third hand.



Insert the photoresistor into the copper holes corresponding.  Make sure that you are putting it in the right way!  



Flip the PCB over and put it back into the vice or third hand face down, so that all of the leads show on the back.  Bend the leads outwards, with the photoresistor a little bit off of the PCB.  Put your soldering iron on one of the junctions where there is a copper hole, and one of the photoresistor legs popping through it.



Wait three seconds, and then take your solder, touch it briefly to the junction, and then take your soldering iron away.  The junction should look something like this volcano shape:



Repeat this process once more to the other joint with the copper hole and a photoresistor leg popping through it.


Trim the leads with your diagonal cutters, so that they don’t poke you.



After you are done, flip the PCB over again so that the text and photoresistor are facing upwards.



Take your 10K (Brown, Black, Orange, Gold) ohm resistor out.



Bend the leads so that they make an upside-down “U” shape. 



Put these two leads into the 10K ohm resistor footprint on the PCB.  



Flip the PCB over and bend the leads of the resistor out in opposite directions.


Solder the two copper holes that have resistor legs popping out of them (using the same method as before).



Trim the leads so they don’t poke you.



Take the 1 pin male header and 4 pin male header, and put them into these Arduino pins:  The 1 pin male header goes into A0, and the 4 pin male header goes into VIN, GND, GND, and +5V as shown below in the picture.  



Place the ArduSensor Light on top of these pins, making sure that the 1 pin male header goes into the 1 pin male header socket, and the 4 pin male header goes into the 4 pin male header.



Solder in place.  But make sure that you don’t put too much solder in, because that can cause the ArduSensor Light to be permanently installed on your Arduino!



Wait for the ArduSensor Light to cool off (around 20-30 seconds), then pull out of the Arduino sockets.  Now you are finished soldering your ArduSensor Light!









If you haven’t downloaded the Arduino IDE, go here to download the latest version.  If you haven’t installed drivers for the Arduino (haven’t downloaded the software yet, or haven’t done this step yet), read the following table:



If you have...

Arduino Uno

Arduino Leonardo


No drivers needed, proceed to the next step

Go here, then proceed


Go here, then proceed

Go here, then proceed



Put in your ArduSensor Button to your Arduino like this: Put the 1 pin male header into A0, and the 4 pin male header in VIN, GND, GND, and +5V.  





Plug in your Arduino with your USB cable (USB-B on the Arduino UNO or earlier, and USB-microB for Arduino Leonardo) to your computer.  Download this zip file and unzip onto your computer.  If you are on a Mac, double click the folder labeled “FishBank-ArduSensor-Light-Example-Code-f78ead3”, double-click the file named “LightRead.ino”, then press OK when the dialogue box pops up. If you are on a Windows computer, press Save instead of Open when you press the download button, double click the folder labeled “FishBank-ArduSensor-Light-Example-Code-f78ead3”, double-click the file named “LightRead.ino,” and then press OK in the pop up box.


The Arduino IDE should open up with the ArduSensor Light Read sketch.  This sketch prints out a number from 0 to 100 on how much light the photoresistor is receiving.


First, make sure to select the board that you are using from Tools > Board.




Then, go into Tools > Serial Port, and select the correct COM/Serial Port.  On a Mac, the usual Serial Port will be /dev/tty.usbmodemfa131.  Any small variation of that will be fine, but make sure to have /dev/tty at the beginning.




On Windows, the COM Port will usually be COM 4, and anything lower or higher might work.


Here are the basic buttons/functions in the Arduino IDE:



Now let’s upload the sketch/code to the Arduino.  Plug one end of the cable into your Arduino, and then the other end into your computer.  Press the Compile + Upload button (Verify if there is any errors in the code, and then upload the sketch/code onto the Arduino), and the program will run on the Arduino.


Press the Serial Monitor button (in the upper-right hand corner), and you should see that it prints out a number between 0 and 100.  Make sure that you have the settings “No line ending” and “9600” for the serial monitor, changeable in the bottom right hand corner.  


If there is lots of light, the reading should be at about 100, and if there is not that much light, the reading should be at about 0.  My lighting was very minimal, and I put my hand over the sensor, to reduce the light, just to demonstrate how this works.



If you have any more questions on this product or how to use it, contact Qtechknow Tech Support at


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