TC02 temperature measurement circuit

The temperature measurement circuit is shown in the figure. In the figure, S1 is the dot/bar display mode conversion switch. When the power supply voltage VCC>8V, LED1~LED10 can be connected without a current limiting resistor in series. The current when the LED is emitting light is set by the external resistors at pins 4 and 6. Assuming that the external resistors at pins 4 and 6 are 1.2kΩ (including R1 and the resistor from the center of BP1 to pin 4), they are connected in parallel with the total resistance of 10kΩ in the voltage divider of LM3914, so that the equivalent resistance between pins 4 and 6 is about 10.7kΩ. The current provided to the voltage divider circuit by the 1.25V reference voltage is 1.25V/1.07kΩ≈1.2mA. The LED emitting current is 10 times this current, that is, about 12mA. This is the advantage of the floating resistor divider. The reference voltage source between pins 7 and 8 is also floating. Pin 6 can be connected to pin 7 to use the internal 1.25V reference voltage, and pin 6 can also be connected to other reference voltages. If RP1 is not used, R1 is connected to pin 4 and then grounded, then the voltage at the top of the resistor divider is 1.25V. Because LM3914 is a linear voltage divider, the in-phase input of the adjacent voltage comparator increases by 0.125V step by step. When the input of pin 5 is zero, all 10 voltage comparators are locked and all LEDs are not lit; when a slowly rising signal voltage is input to pin 5, if it works in bar display mode, one LED will light up for every 0.125V increase in voltage, and all 10 LEDs will light up when it increases to 1.25V. If it works in dynamic point display mode, one LED will light up for every 0.125V increase in input voltage. After using BP1, the potential of pin 4 at the lower end of the resistor divider can be raised, so the range of displayed temperature can be changed. In actual use, changing the resistance value of RP1 can adjust the display range over a large range, while adjusting RP1 can fine-tune the temperature display range.

Component selection: TC02 is a voltage output integrated temperature sensor produced by TELCOM, USA. The output voltage is linearly related to the Celsius temperature. Its main characteristic parameters are: working voltage 3V~12V; typical quiescent current 40mA, maximum 60mA; output sensitivity 100mV/oC; maximum nonlinear error ±0.8℃; typical measurement accuracy is ±0.5℃; temperature measurement range is -40℃~125℃.