Motion Sensing, Optical Isolation, LEDs, Pull up Resistor, Hex Buffer

1
Lecture 4

• Motion Sensing, Optical Isolation, LEDs, Pull up
  Resistor, Hex Buffer

2
Intrusion Circuit

• See schematic for Circuit 3

3
Sensor Control

• When the sensor is activated, a pulse is sent
  which is indicated by the LED
• Also, the LED of the opto-isolator is activated
• The 10K ohm resistor holds the input of the 4049
  Hex Buffer high
• When the opto-isolator turns on, the buffer input
  is pulled low
• This results in a square wave pulse being sent to
  the next circuit acting as a trigger

4
Motion Sensing

• Infrared detection
• Uses a fresnel lens for focusing
• Pronounced frennel
• Detection to 20 feet
• Performance Characteristics
• Current and voltage limitations
• 2 ma at 5 volts

5
Infrared Detection

• IR longer wave length than light
• Lower frequency
• IR will pass through germanium and silicon
  (Light will not)
• Pyrolelectric sensor
• Generates surface electric charge when heated by
  IR
• Transistor activated by charge

6
Fresnel Lens

• Collapsed Plano Complex lens
• See figure

7
LEDs

• Maximum current 20 ma
• Supply 12V
• R V / I 12/.020 600 ohms

8
Optical Isolation

• Separates electrical circuits
• Uses light and light sensitive diode
• Activates a transistor that allows current to
  rush to ground
• Turns on the transistor
• 4N29 performance characteristics
• 2500 Volts isolation
• Max operating temperature 100 deg C

9
Pull up resistor

• With voltage dead headed
• What is the voltage everywhere in wire?
• Resistor limits electron replenishment
• Opto-isolator opens circuit to ground
• Resistor limits current flow
• Voltage after the resistor drops to near zero

10
Hex Buffer

• Digital device
• Output is either high or low
• Device to reverse characteristic of the circuit
• If input high, output low
• If input low, output high