Traditional Chinese Electronic thermometer: Circuit Design, Parts List & Workshop Prototype Guide
In short: Traditional Chinese Electronic thermometer. This entry documents a circuit & prototype taken from Chinese practical-technology literature, written for small-scale makers and home producers. The text below is the full English translation of the original Chinese workshop notes, covering materials and quantities, the step-by-step sequence, and the practical cautions recorded in the source. Roughly 4211 words of English technical text, translated and preserved without editing. It is intended for experimental and reference use, not for regulated or commercial certification.
electronic thermometerThis electronic thermometer uses light-emitting diodes for indication, so it is novel and unique and easy to read, even at night. The measuring range of this thermometer can be freely preset within a wide range. However, its disadvantage is that it can only give segmented indications at fixed points (such as 4 o'clock or 8 o'clock, etc.), but cannot provide continuous indications like ordinary mercury thermometers.The circuit diagram of the device is shown in Figure 4. It consists of a four-op amp integrated circuit 324, four light-emitting diodes, four general diodes 1N4148, a transistor (2N222 or 2N3904), a 2-input four-NAND gate integrated circuit 4011 (only half of it is used) and some RC components.The four operational amplifiers of the 324 are all made into voltage comparators. The inverting input terminals of each operational amplifier are connected in parallel and connected to the thermal diode; each of its non-inverting input terminals is connected to different reference voltage points. The reference voltage is supplied by a 50kΩ semi-variable potentiometer. The total voltage (6V) is obtained from the +9V power supply through a 5kΩ resistor and a 6V Zener diode. Adjusting each 50kΩ potentiometer can obtain different reference voltages (for example, 5, 4, 3, 2V respectively), so that each light-emitting diode emits light at different temperatures. For example, …
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Lei Cheng
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