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McGraw-Hill - The Robot Builder's Bonanza Episode 2 Part 10

Tham khảo tài liệu 'mcgraw-hill - the robot builder's bonanza episode 2 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | USING A PYROELECTRIC SENSOR TO DETECT FIRE 651 Test the circuit by connecting an LED and 270-ohm resistor from the Vout terminal to ground. Point the sensor at a wall and note the condition of the LED. Now wave a match in front of the phototransistor. The LED should blink on and off. You ll notice that the circuit is sensitive to all sources of infrared light which includes the sun strong photolamps and electric burners. If the circuit doesn t seem to be working quite right look for hidden sources of infrared light. With the resistor values shown the circuit is fairly sensitive you can change them by adjusting the value of R1 and R2. WATCHING FOR THE FLICKER OF FIRE No doubt you ve watched a fire at the beach or in a fireplace and noted that the flame changes color depending on the material being burned. Some materials burn yellow or orange while others burn green or blue indeed this is how those specialty fireplace logs burn in different colors . Just like the color signature given off when different materials burn the flames of the fire flicker at different but predictable rates. You can use this so-called flame modulation in a robot fire detection system to determine what is a real fire and what is likely just sunlight streaming through a window or light from a nearby incandescent lamp. By detecting the rate of flicker from a fire and referencing it against known values it is possible to greatly reduce false alarms. The technique is beyond the scope of this book but you could design a simple flame-flicker system using an op amp a fast analog-to-digital converter and a computer or microcontroller. The analog-to-digital converter would translate the instantaneous brightness changes of the fire into digital signals. The patterns made by those signals could then be referenced against those made by known sources of fire. The closer the patterns match the greater the likelihood that there is a real fire. In a commercial product of this nature it is more likely that .