AUTOMATIC ROOM TEMPERATURE FAN SPEED CONTROLLER USING PT-100

SYSTEM DESIGN The system is divided into six main parts, namely, the low-voltage power supply, fixed voltage circuit, sensor & driver circuit, subtraction circuit, buffer circuit and fan dimmer circuit. The sensor & driver circuit consists with PT-100 temperature sensor with associative circuits. The output of the sensor is converted in volts and it use as input of subtraction circuit also the output of fixed voltage circuit is applied to the input of subtraction circuit. The output of subtraction circuit controls the fan dimmer via buffer. The block diagram of the proposed system is depicted. 1 Low-Voltage Power Supply The low-voltage power supply unit consists of transformer X, diode D1, D2 and capacitor C1 [5]. The output of this unit is +12 volt dc which is denoted by +12V. 2 Fixed Voltage Circuit Fixed voltage circuit consists of resistor R1, Zener diode Z1, variable resistor VR1, VR2, VR3 and IC1 [6-7]. In this circuit Zener diode acts as a voltage regulator and IC1 works as a unity follower or buffer circuit. 3 PT-100 Sensor & Driver Circuit PT-100 sensor and driver circuit consists of diode D1, Zener diode Z2, resistor R2-R5, variable resistor VR4, VR5, transistor Q1, Sensor PT-100 and IC2. In this circuit transistor Q1 works as a constant current source to drive the sensor PT-100. Here IC2 works as a buffer to avoid the impedance mismatching. 4 Subtraction Circuit The subtraction circuit consists of IC3, resistor R6 – R9 and variable resistor VR6 [8]. Here VR6 is used to null the offset of this subtraction circuit. 5 Buffer Circuit The buffer circuit consists of IC4 with VR7. Here VR7 set the null offset of the output [9]. 6 Fan Dimmer The fan dimmer circuit consists of resistor R10, R11, opto-coupler, capacitor C2, triac 477DB and SCR TLC226B and fan. Here resistor R10 is used to limit the output current of the buffer circuit.