Thermistor circuit (5)

An electrical appliance requires a sensor that senses the temperature. The appliance operates best in temperatures $0^{\circ}\textrm{C} \leq T \leq 60^{\circ}\textrm{C}$ . When the temperature goes outside this range, a warning LED turns on.

Using the following circuit, with both switches closed and node A connected to ground: The voltage at node B is fed as an analog input signal into a 10-bit ADC (analog to digital converter) with reference voltage $V_{ref} = 1\textrm{V}$ .

As in part 4 : The (NTC) thermistor has a resistance $R_0 = 1875\Omega$ at $T_0 = 25^{\circ}\textrm{C}$ . Its resistance reduces to a fifth of its $25^{\circ}\textrm{C}$ resistance when the temperature is increased to $100^{\circ}\textrm{C}$ .

If the warning LED turns on when the output (in decimal) of the ADC is:

• less than $x$
• greater than $y$

Enter $x+y$ .

Note: Due to the mapping of voltages to discrete output values in the ADC: even when an input is outside the working range of the appliance, if the ADC output is the same value as one inside the range, the warning light will stay off.