Simple household electronic thermometer

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As shown, the transistor base bias resistor R1 is a 3 to 6 kΩ thermistor. When the room temperature rises, the R1 block becomes smaller, and the base voltage of the transistor increases, and the change in the collector current is displayed on the ammeter M. If you choose a 4 volt regulator, the transistor's β>50, you can use 0 ~ 30mA ammeter.
After the production is completed, the current meter scale can be checked with hot water, ice cubes and a standard watermark thermometer, and the circuit expression indication is changed to temperature reading. If you add a thermistor with the same characteristics and a switch changer, you can also test the external temperature, but a thermistor needs to be outside.