{"id":5580,"date":"2024-01-10T23:30:03","date_gmt":"2024-01-10T18:00:03","guid":{"rendered":"https:\/\/electrocredible.com\/?p=5580"},"modified":"2024-02-18T15:16:14","modified_gmt":"2024-02-18T09:46:14","slug":"raspberry-pi-pico-ldr-photoresistor-light-dark-sensor","status":"publish","type":"post","link":"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/","title":{"rendered":"Raspberry Pi Pico LDR(Photoresistor) Interfacing Guide &#8211; Light\/Dark Sensor"},"content":{"rendered":"\n<p>This tutorial will guide you to interface an LDR\/photoresistor with Raspberry Pi Pico W. LDR (Light Dependent Resistor) is an electronic sensor commonly used in electronic circuits for applications such as light-sensitive switches.<\/p>\n\n\n\n<p>MicroPython code is used here to read analog values from an LDR. Detailed steps are shown to control AC appliances based on light sensed by LDR.<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_65 counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title \" >Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #000000;color:#000000\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #000000;color:#000000\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Components_Required\" title=\"Components Required\">Components Required<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Brief_Overview-_LDR_or_Photoresistor\" title=\"Brief Overview- LDR or Photoresistor\">Brief Overview- LDR or Photoresistor<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#How_to_Read_LDR_Using_Raspberry_Pi_Pico\" title=\"How to Read LDR Using Raspberry Pi Pico \">How to Read LDR Using Raspberry Pi Pico <\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Wiring_LDR_with_Raspberry_Pi_Pico\" title=\"Wiring LDR with Raspberry Pi Pico\">Wiring LDR with Raspberry Pi Pico<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#LDR_MicroPython_Code\" title=\"LDR MicroPython Code\">LDR MicroPython Code<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Understanding_Data_from_the_Photoresistor\" title=\"Understanding Data from the Photoresistor\">Understanding Data from the Photoresistor<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Demonstration\" title=\"Demonstration\">Demonstration<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Sense_Light_Darkness_using_LDR_Raspberry_Pi_Pico_W\" title=\"Sense Light\/ Darkness using LDR &amp; Raspberry Pi Pico W\">Sense Light\/ Darkness using LDR &amp; Raspberry Pi Pico W<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#DarkLight_Detector_Circuit-_Control_AC_Appliances\" title=\"Dark\/Light Detector Circuit- Control AC Appliances\">Dark\/Light Detector Circuit- Control AC Appliances<\/a><ul class='ez-toc-list-level-4' ><li class='ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Schematic_Photoresistor-controlled_AC_Bulb\" title=\"Schematic: Photoresistor-controlled AC Bulb\">Schematic: Photoresistor-controlled AC Bulb<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Dark_Sensor_MicroPython_Code\" title=\"Dark Sensor MicroPython Code\">Dark Sensor MicroPython Code<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Light_Sensor_MicroPython_Code\" title=\"Light Sensor MicroPython Code\">Light Sensor MicroPython Code<\/a><\/li><\/ul><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-ldr-photoresistor-light-dark-sensor\/#Conclusion\" title=\"Conclusion\">Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Components_Required\"><\/span>Components Required<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ol>\n<li>Raspberry Pi Pico or Pico W.<\/li>\n\n\n\n<li>An LDR.<\/li>\n\n\n\n<li>A 10k\u03a9 resistor.<\/li>\n\n\n\n<li>Breadboard and connecting wires.<\/li>\n\n\n\n<li>5V Relay module (optional).<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Brief_Overview-_LDR_or_Photoresistor\"><\/span>Brief Overview- LDR or Photoresistor<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>A Light Dependent Resistor (LDR) is a photoconductive device whose electrical resistance varies with light intensity. LDRs are commonly used in devices like automatic streetlights that get triggered on\/off based on sunlight.<\/p>\n\n\n\n<p>When there&#8217;s a lot of light, the LDR&#8217;s resistance decreases. In other words, it allows more electric current to flow through it. In low light or darkness, the LDR&#8217;s resistance increases, restricting the flow of electric current.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"493\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-Resistance-change-in-light-and-darkness.webp\" alt=\"\" class=\"wp-image-5805\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-Resistance-change-in-light-and-darkness.webp 700w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-Resistance-change-in-light-and-darkness-300x211.webp 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><figcaption class=\"wp-element-caption\">How the resistance of a photoresistor changes with light intensity<\/figcaption><\/figure>\n\n\n\n<p>You can test a photoresistor by setting your multimeter to the resistance sensing position and connecting the multimeter leads to the legs of the LDR. See how the resistance changes when you cover the sensor with your hand. When I tested in total darkness, the resistance was more than 1 megaOhm. When the LDR was moved close to a light bulb, its resistance dropped to around 100 Ohms. <\/p>\n\n\n\n<p>Photoresistors are also available as modules as shown below. These modules come with an onboard potentiometer, comparator, and other passive components so it becomes easy to interface.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"600\" height=\"489\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-module.webp\" alt=\"\" class=\"wp-image-5806\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-module.webp 600w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-module-300x245.webp 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Photoresistor module<\/figcaption><\/figure>\n\n\n\n<p>Such LDR modules can control relays without the need for a microcontroller. However, setting the threshold can be tricky through trial and error.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"How_to_Read_LDR_Using_Raspberry_Pi_Pico\"><\/span>How to Read LDR Using Raspberry Pi Pico <span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Due to the resistive nature of a photoresistor, we can use it in series with another resistor to form a <a href=\"https:\/\/electrocredible.com\/voltage-divider-circuit-basics-formula-types-applications\/\" target=\"_blank\" data-type=\"post\" data-id=\"2983\" rel=\"noreferrer noopener\">voltage divider<\/a>. <\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"638\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/06\/resistive-voltage-divider-circuit-1024x638.webp\" alt=\"resistive voltage divider circuit diagram\" class=\"wp-image-3374\" style=\"width:600px\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/06\/resistive-voltage-divider-circuit-1024x638.webp 1024w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/06\/resistive-voltage-divider-circuit-300x187.webp 300w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/06\/resistive-voltage-divider-circuit-768x479.webp 768w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/06\/resistive-voltage-divider-circuit.webp 1089w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p>Instead of <em>R<sub>1<\/sub><\/em>, we will connect the LDR. A 10k\u03a9 resistor will replace R2. <\/p>\n\n\n\n<p>The output of a voltage divider depends on the total voltage supplied across the resistors and the value of the resistors. As the resistance of an LDR changes with the intensity of light falling on it, we will get a variable output voltage depending on light intensity. This voltage can be measured by Raspberry Pi Pico with the help of an ADC. <\/p>\n\n\n\n<p>ADC( Analog-to-digital converter) are circuits that help to read real-world analog voltages by converting them to digital data. Raspberry Pi Pico\/Pico W has three pins for ADC that give access to three inbuilt ADCs.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>ADC Channel<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\"><strong>GPIO Pin<\/strong><\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\">ADC0<\/td><td class=\"has-text-align-center\" data-align=\"center\">GPIO 26<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\">ADC1<\/td><td class=\"has-text-align-center\" data-align=\"center\">GPIO 27<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\">ADC2<\/td><td class=\"has-text-align-center\" data-align=\"center\">GPIO 28<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>To learn more about ADC, read <a href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-adc-micropython-potentiometer\/\" data-type=\"post\" data-id=\"1517\" target=\"_blank\" rel=\"noreferrer noopener\">how to use the ADC in Raspberry Pi Pico<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Wiring_LDR_with_Raspberry_Pi_Pico\"><\/span>Wiring LDR with Raspberry Pi Pico<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Connect one terminal of the LDR to the 3.3 volts output pin onboard Raspberry Pi Pico. Connect the other terminal of the LDR to one terminal of a 10k\u03a9 resistor. The remaining terminal of the 10k\u03a9 resistor connects to the Ground. (Tip: The third pin from any corner of Raspberry Pi Pico is a GND pin).<\/p>\n\n\n\n<p>We have used <strong>GPIO 28<\/strong> to read the output of the voltage divider, but you can also use <strong>GPIO 26<\/strong> or <strong>GPIO 27<\/strong>.  <strong>GPIO 28<\/strong> is the 7th pin from the top right corner of Pico.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"744\" height=\"536\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-PICO-W-SCHEMATIC.webp\" alt=\"\" class=\"wp-image-5807\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-PICO-W-SCHEMATIC.webp 744w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-PICO-W-SCHEMATIC-300x216.webp 300w\" sizes=\"(max-width: 744px) 100vw, 744px\" \/><figcaption class=\"wp-element-caption\">Schematic of Raspberry Pi Pico W with an LDR<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"564\" height=\"913\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-with-Pico-on-breadboard.webp\" alt=\"\" class=\"wp-image-5808\" style=\"width:300px\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-with-Pico-on-breadboard.webp 564w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-with-Pico-on-breadboard-185x300.webp 185w\" sizes=\"(max-width: 564px) 100vw, 564px\" \/><figcaption class=\"wp-element-caption\">Raspberry Pi Pico W connected with LDR on a breadboard.<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"LDR_MicroPython_Code\"><\/span>LDR MicroPython Code<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Raspberry Pi Pico needs to be flashed with a<a href=\"https:\/\/micropython.org\/download\/\" target=\"_blank\" rel=\"noopener\"> <strong>MicroPython UF2<\/strong><\/a> file to program it in MicroPython. You can read our<a href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-tutorial-for-beginners\/\"> getting started guide for Raspberry Pi Pico<\/a> where we show all the steps required to start programming Raspberry Pi Pico &amp; Pico W.<\/p>\n\n\n\n<p>The steps to upload MicroPython code are explained using Thonny IDE.<\/p>\n\n\n\n<p>1. With all connections done according to the above schematic, connect the Pico to your computer using a USB cable. Open Thonny IDE and set the interpreter to use MicroPython on Raspberry Pi Pico.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"835\" height=\"523\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/12\/Thonny-IDE-select-interpreter-as-MicroPython-Raspberry-Pi-Pico.webp\" alt=\"Thonny IDE select interpreter as MicroPython Raspberry Pi Pico\" class=\"wp-image-5532\" style=\"width:700px\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/12\/Thonny-IDE-select-interpreter-as-MicroPython-Raspberry-Pi-Pico.webp 835w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/12\/Thonny-IDE-select-interpreter-as-MicroPython-Raspberry-Pi-Pico-300x188.webp 300w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/12\/Thonny-IDE-select-interpreter-as-MicroPython-Raspberry-Pi-Pico-768x481.webp 768w\" sizes=\"(max-width: 835px) 100vw, 835px\" \/><\/figure>\n\n\n\n<p>&nbsp;2. Paste the following code into a new project.(<strong>File<\/strong>&gt;<strong>New<\/strong> in Thonny IDE)<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">from<\/span> machine <span class=\"hljs-keyword\">import<\/span> ADC\n<span class=\"hljs-keyword\">import<\/span> time\nadc = ADC(<span class=\"hljs-number\">28<\/span>) \n<span class=\"hljs-keyword\">while<\/span> <span class=\"hljs-literal\">True<\/span>:\n    digital_value = adc.read_u16()     \n    print(<span class=\"hljs-string\">\"ADC value=\"<\/span>,digital_value)\n    volt=<span class=\"hljs-number\">3.3<\/span>*(digital_value\/<span class=\"hljs-number\">65535<\/span>)\n    print(<span class=\"hljs-string\">\"Voltage: {}V \"<\/span>.format(volt))\n    time.sleep(<span class=\"hljs-number\">1<\/span>)\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>3. Click on <strong>File<\/strong>&gt;<strong>Save as<\/strong> and select the save location as Raspberry Pi Pico.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"312\" height=\"268\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/06\/save-to.webp\" alt=\"Thonny Save to\" class=\"wp-image-379\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/06\/save-to.webp 312w, https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/06\/save-to-300x258.webp 300w\" sizes=\"(max-width: 312px) 100vw, 312px\" \/><\/figure>\n\n\n\n<p>4. Name the code file as <strong>main.py<\/strong>.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"655\" height=\"427\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/11\/save-as-main.py-in-Thonny-Pi-Pico-1-1.webp\" alt=\"main.py\" class=\"wp-image-5200\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/11\/save-as-main.py-in-Thonny-Pi-Pico-1-1.webp 655w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/11\/save-as-main.py-in-Thonny-Pi-Pico-1-1-300x196.webp 300w\" sizes=\"(max-width: 655px) 100vw, 655px\" \/><\/figure>\n\n\n\n<p>5. Run the code by clicking the <strong>Run<\/strong> icon or by pressing the <strong>F5 <\/strong>key<strong>.<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"785\" height=\"285\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/05\/run-button-Thonny-1.webp\" alt=\"run-button-Thonny-1\" class=\"wp-image-176\" style=\"width:600px\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/05\/run-button-Thonny-1.webp 785w, https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/05\/run-button-Thonny-1-300x109.webp 300w, https:\/\/electrocredible.com\/wp-content\/uploads\/2022\/05\/run-button-Thonny-1-768x279.webp 768w\" sizes=\"(max-width: 785px) 100vw, 785px\" \/><\/figure>\n\n\n\n<p>Now, in the shell of Thonny IDE, you can view the output voltage from the voltage divider connected to the LDR. <\/p>\n\n\n\n<p>You can also view the plot of ADC value in the inbuilt plotter of Thonny IDE. Click on <strong>View<\/strong>&gt;<strong>Plotter<\/strong> to view the plotter. Here is a screenshot of the plotter showing ADC data when I covered the light sensor with my hand and then removed the hand after a few seconds:<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"325\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/Thonny-IDE-shell-showing-ADC-data-plot-obtained-from-LDR-.webp\" alt=\"\" class=\"wp-image-5810\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/Thonny-IDE-shell-showing-ADC-data-plot-obtained-from-LDR-.webp 700w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/Thonny-IDE-shell-showing-ADC-data-plot-obtained-from-LDR--300x139.webp 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><figcaption class=\"wp-element-caption\">Plot of ADC values while light intensity falling on an LDR is varied<\/figcaption><\/figure>\n\n\n\n<p>Note: Only print one value for plotting. Comment out other <code>print<\/code> statements from your code.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Understanding_Data_from_the_Photoresistor\"><\/span>Understanding Data from the Photoresistor<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>If you move the photoresistor from light to darkness, the output voltage printed in the shell of your IDE will change from a higher value to a lower value.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"496\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-light-to-darkness-.webp\" alt=\"\" class=\"wp-image-5811\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-light-to-darkness-.webp 700w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-light-to-darkness--300x213.webp 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><\/figure>\n\n\n\n<p>The formula for the output voltage of the voltage divider formed by series resistors <em>R<sub>1<\/sub><\/em> &amp; <em>R<sub>2<\/sub> <\/em> is: <\/p>\n\n\n\n<p class=\"has-text-align-center\">$V_{out}= Vin\\;\\times\\;\\left( \\frac{R_{2}}{R_{1}+ R_{2}} \\right)$<\/p>\n\n\n\n<p>Here, the photoresistor replaces <strong>R<sub style=\"\">1<\/sub><\/strong>. The 10k\u03a9 resistor replaces <strong>R2<\/strong>. The resistance of the LDR (<strong>R1<\/strong>) increases when moving from a well-lit area to a dark one. So, the output voltage of the voltage divider will decrease. This is evident in the output printed in the shell of the IDE.<\/p>\n\n\n\n<p>The image below shows the output when LDR is moved from a dark area to a bright area &#8211; the voltage read by ADC increases.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"451\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-dark-to-light-.webp\" alt=\"\" class=\"wp-image-5812\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-dark-to-light-.webp 700w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/ldr-change-in-voltage-when-sensor-moved-from-dark-to-light--300x193.webp 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Demonstration\"><\/span>Demonstration<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The animation below demonstrates how the output in the shell of Thonny IDE varies as I change the amount of light falling on the photoresistor.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"600\" height=\"338\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/02\/Raspberry-Pi-Pico-LDR-demostration.webp\" alt=\"\" class=\"wp-image-6333\"\/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Sense_Light_Darkness_using_LDR_Raspberry_Pi_Pico_W\"><\/span>Sense Light\/ Darkness using LDR &amp; Raspberry Pi Pico W<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>We can apply the methods described so far to build projects such as automatic lights. Such lights can switch on\/off automatically according to ambient light.<\/p>\n\n\n\n<p>Here are two examples of how we can control AC appliances that can turn off when the LDR detects light or darkness.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"DarkLight_Detector_Circuit-_Control_AC_Appliances\"><\/span>Dark\/Light Detector Circuit- Control AC Appliances<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>To control AC appliances, we need to interface with a relay module. Relays are electromechanical switches that help to interface low-voltage devices such as microcontrollers to high-voltage devices such as AC bulbs or fans.<\/p>\n\n\n\n<p>Take a look at our <a href=\"https:\/\/electrocredible.com\/raspberry-pi-pico-relay-control-using-web-server\/\" data-type=\"post\" data-id=\"2078\">guide on interfacing relays with Raspberry Pi Pico<\/a> where we thoroughly explain how to control relays.<\/p>\n\n\n\n<p>We shall use a commonly available relay module as shown below. A single-channel relay module will work, but here we have explained using a 2-channel relay.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"586\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/02\/2-channel-relay-module-pinout-1024x586.webp\" alt=\"2 channel relay module pinout diagram\" class=\"wp-image-2140\" style=\"width:600px;height:auto\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/02\/2-channel-relay-module-pinout-1024x586.webp 1024w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/02\/2-channel-relay-module-pinout-300x172.webp 300w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/02\/2-channel-relay-module-pinout-768x439.webp 768w, https:\/\/electrocredible.com\/wp-content\/uploads\/2023\/02\/2-channel-relay-module-pinout.webp 1211w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p>Each channel of a relay module lets us control an appliance independently. The common pin (<strong>COM<\/strong>) either makes contact with the <strong>NO<\/strong> or <strong>NC<\/strong> terminal, depending on the state of the relay. When the relay is not powered, the Normally Open (<strong>NO<\/strong>) terminal stays open and the Normally Connected (<strong>NC<\/strong>) terminal is shorted to <strong>COM<\/strong>. The reverse condition occurs when the relay is powered.<\/p>\n\n\n\n<p>The two input pins <strong>IN1<\/strong> and <strong>IN2<\/strong> control the two relays. Connecting these pins to the ground(or VCC in some modules) will switch on the respective relays.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Schematic_Photoresistor-controlled_AC_Bulb\"><\/span>Schematic: Photoresistor-controlled AC Bulb<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>The relay module is powered from 5V via the <strong>VBUS<\/strong> pin of Pico W. <strong>GPIO 16<\/strong> sends the control signal to the relay. One relay out of the two is left unused. <\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"693\" src=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-pico-relay-circuit-1024x693.webp\" alt=\"\" class=\"wp-image-5813\" style=\"width:800px\" srcset=\"https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-pico-relay-circuit-1024x693.webp 1024w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-pico-relay-circuit-300x203.webp 300w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-pico-relay-circuit-768x520.webp 768w, https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-pico-relay-circuit.webp 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Schematic for controlling AC appliances using Raspberry Pi Pico and LDR<\/figcaption><\/figure>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Dark_Sensor_MicroPython_Code\"><\/span>Dark Sensor MicroPython Code<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">from<\/span> machine <span class=\"hljs-keyword\">import<\/span> ADC, Pin\n<span class=\"hljs-keyword\">import<\/span> time\nadc = ADC(<span class=\"hljs-number\">28<\/span>) <span class=\"hljs-comment\">#pin to read LDR <\/span>\nrelay_pin=Pin(<span class=\"hljs-number\">16<\/span>, Pin.OUT) <span class=\"hljs-comment\">#pin connected to relay module<\/span>\n<span class=\"hljs-keyword\">while<\/span> <span class=\"hljs-literal\">True<\/span>:\n    digital_value = adc.read_u16()     \n    volt=<span class=\"hljs-number\">3.3<\/span>*(digital_value\/<span class=\"hljs-number\">65535<\/span>)\n    <span class=\"hljs-keyword\">if<\/span> volt&lt;<span class=\"hljs-number\">1<\/span>:\n        relay_pin.value(<span class=\"hljs-number\">0<\/span>) <span class=\"hljs-comment\">#turns on the relay<\/span>\n    <span class=\"hljs-keyword\">if<\/span> volt&gt;<span class=\"hljs-number\">1.2<\/span>:\n        relay_pin.value(<span class=\"hljs-number\">1<\/span>) <span class=\"hljs-comment\">#turns off the relay<\/span>\n    time.sleep(<span class=\"hljs-number\">1<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>This MicroPython code will switch on the AC bulb when the light falling on the LDR goes below a certain threshold. If the light intensity crosses another threshold, the bulb will switch off.<\/p>\n\n\n\n<p>The reason for including two threshold values in the code is to add <a href=\"https:\/\/en.wikipedia.org\/wiki\/Hysteresis\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">hysteresis<\/a>. Otherwise, the bulb may oscillate between on and off states when the value is close to the threshold.<\/p>\n\n\n\n<p>Note that the code <code>relay_pin.value(1)<\/code> turns off the relay. Usually, a relay module turns off when we send +5V to the input pin. But you may also find some modules that turn off by the code <code>relay_pin.value(1)<\/code>.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Light_Sensor_MicroPython_Code\"><\/span>Light Sensor MicroPython Code<span class=\"ez-toc-section-end\"><\/span><\/h4>\n\n\n\n<p>The same code as above may be slightly modified if we want to turn off an appliance when light falls on the photoresistor.<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"Python\" data-shcb-language-slug=\"python\"><span><code class=\"hljs language-python\"><span class=\"hljs-keyword\">from<\/span> machine <span class=\"hljs-keyword\">import<\/span> ADC, Pin\n<span class=\"hljs-keyword\">import<\/span> time\nadc = ADC(<span class=\"hljs-number\">28<\/span>) <span class=\"hljs-comment\">#pin to read LDR <\/span>\nrelay_pin=Pin(<span class=\"hljs-string\">'LED'<\/span>, Pin.OUT) <span class=\"hljs-comment\">#pin connected to relay module<\/span>\n<span class=\"hljs-keyword\">while<\/span> <span class=\"hljs-literal\">True<\/span>:\n    digital_value = adc.read_u16()     \n    volt=<span class=\"hljs-number\">3.3<\/span>*(digital_value\/<span class=\"hljs-number\">65535<\/span>)\n    <span class=\"hljs-keyword\">if<\/span> volt&lt;<span class=\"hljs-number\">1<\/span>:\n        relay_pin.value(<span class=\"hljs-number\">1<\/span>) <span class=\"hljs-comment\">#turns off the relay<\/span>\n    <span class=\"hljs-keyword\">if<\/span> volt&gt;<span class=\"hljs-number\">1.2<\/span>:\n        relay_pin.value(<span class=\"hljs-number\">0<\/span>) <span class=\"hljs-comment\">#turns on the relay<\/span>\n    time.sleep(<span class=\"hljs-number\">1<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">Python<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">python<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Conclusion\"><\/span>Conclusion<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>In this guide, we discussed how we can interface an LDR with Raspberry Pi Pico W. We also explained a basic application circuit that can detect light\/darkness and control AC appliances such as home lighting.<\/p>\n\n\n\n<p>You may use this information to build more projects such as solar panel sun trackers, automatic curtains, automatic night lamps, etc. <\/p>\n","protected":false},"excerpt":{"rendered":"<p>This tutorial will guide you to interface an LDR\/photoresistor with Raspberry Pi Pico W. LDR (Light Dependent Resistor) is an electronic sensor commonly used in electronic circuits for applications such as light-sensitive switches. MicroPython code is used here to read analog values from an LDR. Detailed steps are shown to control AC appliances based on [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":5815,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","footnotes":""},"categories":[11],"tags":[8,14],"uagb_featured_image_src":{"full":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE.webp",1200,628,false],"thumbnail":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE-150x150.webp",150,150,true],"medium":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE-300x157.webp",300,157,true],"medium_large":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE-768x402.webp",768,402,true],"large":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE-1024x536.webp",1024,536,true],"1536x1536":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE.webp",1200,628,false],"2048x2048":["https:\/\/electrocredible.com\/wp-content\/uploads\/2024\/01\/LDR-RASPBERRY-PI-PICO-FEATURED-IMAGE.webp",1200,628,false]},"uagb_author_info":{"display_name":"Abhilekh Das","author_link":"https:\/\/electrocredible.com\/author\/abhilekh-2\/"},"uagb_comment_info":0,"uagb_excerpt":"This tutorial will guide you to interface an LDR\/photoresistor with Raspberry Pi Pico W. LDR (Light Dependent Resistor) is an electronic sensor commonly used in electronic circuits for applications such as light-sensitive switches. MicroPython code is used here to read analog values from an LDR. Detailed steps are shown to control AC appliances based on&hellip;","_links":{"self":[{"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/posts\/5580"}],"collection":[{"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/comments?post=5580"}],"version-history":[{"count":122,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/posts\/5580\/revisions"}],"predecessor-version":[{"id":6335,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/posts\/5580\/revisions\/6335"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/media\/5815"}],"wp:attachment":[{"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/media?parent=5580"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/categories?post=5580"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/electrocredible.com\/wp-json\/wp\/v2\/tags?post=5580"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}