Rd 3 - Electronics • Ohm’s Law • Potential Divider • Resistor in Series and Parallel • - Application of Ohm’s Law • 4. Operational Amplifier (Comparator and Gain) • 5. Switches and Relay
Using Operational Amplifier to control Music IC 9V Battery 1 SPDT Switch Thermistor Variable Resistor 10K Resistor (*3) 3140 Op_amp TIP121 Transistor IN4148 Diode M66T Music IC 8 Ohm Speaker 3V Battery Connector 1 SPDT Relay 220uF Capacitor 9 Volt Circuit 3 Volt Music IC
Circuit Symbol 3140 Op-Amp An integrated circuit consisting of a silicon chip in a plastic 8 pin package Contains 20 transistors eleven resistors and one capacitor. Typical uses: - Voltage comparator, High gain amplifier
Op-Amp as a Comparator Compares the voltage at pin 2 to the voltage at pin 3 If V3 > V2 the output is high (on) If V3 < V2 the output is low (off) Voltage at pin 2 = threshold or reference voltage
Darlington Pair A special arrangement of two transistors (often called a DarlingtonPair) is shown in the diagram opposite. There are number of situations in which we might make use this configuration. What are the advantage of using an arrangement such as this? • It is much more sensitive • The TIP121 is a form of Darlington pair and can carry up to 1 amp of current. Most transistors carry 100mA • Only a tiny base current is needed as the gain is around 1000 • Note however that this transistor switches at 1.2V Why?
Potential Divider – DPDT motor control (Reversal) 9 Volt Battery Clip 3V Battery Clip 3 Terminal Blocks 1k resistor BC337 Transistor 1N4148 Diode Red LED 470 Ohm Resistor 1 DPDT relay 1 Toggle Switch 1 SPST Switch 2 Microswitches Motor
Variable Resistor Variable resistors consist of a resistance material with connections at both ends and a wiper which moves along the track as the arm is rotated through 270°. The track is normally rotary but straight track versions, usually called sliders, are sometimes used. The further clockwise the wiper is rotated, the larger the resistance.
T b T a P 1 P 2