Simple household electronic thermometer

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