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<\/p>\nThis four-level thermometer is a simple and reliable electronic system designed to monitor the ambient temperature inside a room. It uses four colored LEDs (blue, green, yellow, and red) to indicate different temperature thresholds. The blue LED lights up when it is cold, the green LED indicates an ideal temperature (around 20\u201325\u202f\u00b0C), the yellow LED signals moderate heat, and the red LED turns on if the temperature exceeds a high threshold (above 30\u202f\u00b0C, for example). This intuitive display is perfect for use in spaces such as a bedroom, kitchen, or office.<\/p>\n
The circuit is based on the LM324 quad op-amp, a very common component in analog applications. It contains four independent amplifiers in a DIP-14 package, operating with a single supply from +3\u202fV to +32\u202fV (or \u00b11.5\u202fV to \u00b116\u202fV). It features low power consumption (1\u202fmA typical), a 1\u202fMHz bandwidth, and a slew rate of 0.5\u202fV\/\u00b5s. In this setup, each integrated comparator compares the voltage generated by the thermistor with a specific reference voltage, triggering the corresponding LED based on the measured temperature range.<\/p>\n
The temperature sensor used is a 100k\u2126 NTC thermistor MF52AT, a Negative Temperature Coefficient sensor whose resistance decreases as temperature increases. At 25\u202f\u00b0C, its resistance is precisely 100\u202fk\u2126 with a \u00b11% tolerance. It has a B coefficient of 3950\u202fK, offering good accuracy for ambient temperature measurement applications. The output voltage from the voltage divider (with a fixed resistor) changes predictably with temperature, allowing effective comparison via the LM324 comparator inputs.<\/p>\n
To ensure clear visualization and prevent multiple LEDs from lighting up simultaneously, the circuit uses three NPN transistors of type 2N3904. This standard small transistor can handle a collector current up to 200\u202fmA, with a typical current gain (hFE) of 100 to 300, and a transition frequency ft of 300\u202fMHz. They act as switches to automatically turn off the LEDs that do not match the current temperature, thus ensuring accurate indication.<\/p>\n
The entire setup is powered by regulated 5\u202fV supplied by an L7805 voltage regulator. This linear regulator can deliver up to 1\u202fA of output current, with a minimum input voltage of 7.5\u202fV, and includes protection against overheating and short circuits. It ensures a stable voltage, essential for reliable comparator thresholds in an analog system.<\/p>\n
In addition to its main function, this setup can also serve as a decorative night light, thanks to its colored LEDs creating a subtle ambient glow. Its simple design, low cost, and moderate power consumption make it an ideal project for electronics hobbyists looking to combine utility and aesthetics.<\/p>\n
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The MF52AT NTC thermistor is a Negative Temperature Coefficient temperature sensor, meaning its resistance decreases as temperature increases. This type of sensor is widely used for temperature measurement applications due to its high accuracy and ease of use. The MF52AT has a nominal resistance of 100\u202fk\u2126 at 25\u202f\u00b0C, making it an ideal choice for thermal monitoring projects requiring a moderate temperature range. Its B coefficient is approximately 3950\u202fK, meaning the relationship between temperature and resistance is well defined, allowing accurate measurements when used in a voltage divider circuit.<\/p>\n
One advantage of this thermistor is its fast response to temperature changes, enabling almost instant detection of ambient temperature variations. It also offers very good long-term stability, which is essential for applications where reliability is critical. The temperature range of the MF52AT typically extends from -40\u202f\u00b0C to +125\u202f\u00b0C, making it suitable for a wide range of domestic and industrial applications. Depending on the required precision, calibration or compensation may be necessary for the most critical applications.<\/p>\n
This thermistor is frequently used in simple circuits, such as LED thermometers, temperature controllers, or even overheat protection devices. Thanks to its small size and low power consumption, it remains a popular choice for low-cost electronic projects.<\/p>\n
The LM324 is a widely used quad operational amplifier in electronic circuits due to its low cost and characteristics suited for a wide range of applications. This component includes four independent operational amplifiers, allowing several comparators or filters to be built with a single IC. The LM324 operates under a supply voltage ranging from 3\u202fV to 32\u202fV (or \u00b11.5\u202fV to \u00b116\u202fV with a dual supply), making it very flexible for both low- and high-voltage designs. It typically consumes 1\u202fmA per channel, which is especially advantageous for low-power circuits.<\/p>\n
The LM324 offers a 1\u202fMHz bandwidth at unity gain, sufficient for many analog applications, though it is less suitable for high-frequency circuits. The slew rate is 0.5\u202fV\/\u00b5s, providing a good balance between speed and accuracy for most common uses. This IC also has a typical input offset voltage of 2\u202fmV, and it can be used with input voltages close to ground (0\u202fV), which is useful for systems requiring measurements near zero.<\/p>\n
The LM324 is thus particularly suitable for applications such as active filters, voltage comparators, non-inverting amplifiers, and signal conditioning circuits. Thanks to its robustness and ease of use, it remains a popular component in analog electronics.<\/p>\n
The L7805 is a linear voltage regulator from the 78xx series, designed to provide a fixed +5\u202fV output voltage. It is one of the most commonly used regulators in electronic circuits requiring a stable power supply, especially for powering microcontrollers, sensors, or logic modules. The L7805 typically operates with an input voltage between 7\u202fV and 20\u202fV, although the maximum range can go up to 35\u202fV depending on the version. To ensure proper regulation, it is recommended to maintain a minimum 2\u202fV difference between input and output (dropout voltage).<\/p>\n
This component can provide up to 1\u202fA output current, and some versions with heatsinks can go up to 1.5\u202fA. It features built-in protection against short circuits, overheating, and overcurrent, making it highly reliable in a variety of environments. The L7805 is often used with filtering capacitors (typically 0.33\u202f\u00b5F at the input and 0.1\u202f\u00b5F at the output) to improve stability and reduce oscillations.<\/p>\n
Thanks to its ease of implementation, robustness, and low cost, the L7805 remains an essential component for many electronic projects requiring regulated 5\u202fV power, especially in robotics, home automation, or embedded electronics.<\/p>\n
The 2N3904 is a widely used NPN bipolar junction transistor for amplification or switching functions in electronic circuits. It is designed for low-power applications, with a maximum collector-emitter voltage (Vce) of 40\u202fV and a maximum base-emitter voltage (Vbe) of 6\u202fV. This transistor can handle a collector current (Ic) up to 200\u202fmA, making it ideal for driving LEDs, relays, or small motors. Its typical DC current gain (hFE) ranges from 100 to 300, ensuring good amplification in standard circuits.<\/p>\n
The transition frequency (ft) of the 2N3904 is about 300\u202fMHz, making it suitable for high-frequency applications in RF or audio circuits. It also features fast switching time, generally under 300\u202fns, making it useful in digital or PWM circuits. Lightweight, cost-effective, and easy to integrate (TO-92 package), the 2N3904 is an ideal choice for both electronics enthusiasts and professionals.<\/p>\n","protected":false},"excerpt":{"rendered":"
This four-level thermometer is a simple and reliable electronic system designed to monitor the ambient temperature inside a room. It uses four colored LEDs (blue, green, yellow, and red) to indicate different temperature thresholds. The blue LED lights up when it is cold, the green LED indicates an ideal temperature (around 20\u201325\u202f\u00b0C), the yellow LED… 4-Level LED household thermometer<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":803,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"off","neve_meta_content_width":70,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","iawp_total_views":17,"footnotes":""},"categories":[2],"tags":[],"class_list":["post-802","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-projects"],"_links":{"self":[{"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/posts\/802","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/comments?post=802"}],"version-history":[{"count":5,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/posts\/802\/revisions"}],"predecessor-version":[{"id":809,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/posts\/802\/revisions\/809"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/media\/803"}],"wp:attachment":[{"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/media?parent=802"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/categories?post=802"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.zonetronik.com\/en\/wp-json\/wp\/v2\/tags?post=802"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}