Withdrawn. UVFL UltraViolet Flame sensor $149.00
This sensor is no longer available. It is listed here for reference only.
The UV Flame sensor detects candle flame and other sources of Ultraviolet light..
The UV Flame sensor is intended for use with the Lego Mindstorms™ Robotic Invention System. It may be used with either the RCX or the NXT controller. Connection to the NXT requires a NXT conversion cable (W770323). The sensor is intended to help your robot find a candle and go to it, as in a robotic firefighting competition. The sensor detects the presence of ultraviolet light. Ultraviolet (UV) is like normal light, except you can not see it with you eye. UV light does not pass through normal glass or most clear plastics.
DANGER! The sensor uses an ionization tube that runs at 350 volts. This voltage is dangerous! Do not operate the sensor if it is wet or the glass tube is broken. This product should only be used with adult supervision.
Connect the sensor to the NXT using a NXT conversion cable (W770323) The UV Flame Sensor is a Boolean (yes/no) device. You can program it like a light* sensor detecting light or no light. . When it is not detecting UV light the output is 1020 Raw. When it detects UV light it produces a pulse with a value around 550 Raw. The output pulse is 100 milliseconds long. You should read the sensor frequently or you may miss the pulse. The sensor is best programmed using the custom Techno-stuff Flame Sensor Block You can download the custom block here. Follow these directions to install the block After installing you should see the flame sensor block in the "Complete Palette" view.
In the example program below set the sound block to beep for 0.1 second. The program will beep rapidly when a flame is near the sensor.
The UV Flame Sensor is a Boolean (yes/no) device. You program it like a light sensor detecting light or no light. . When it is not detecting UV light the output is zero. (Light sensor scaled) When it detects UV light it produces a pulse with a value around 75. The output pulse is 100 milliseconds long. You should read the sensor frequently or you may miss the pulse. The RIS program below will beep rapidly when a flame is near the sensor.
With Robolab, the sensor is best used as an event source. Use the “Light sensor event” block to set up the UV Flame Sensor. The program below sets up the UV Flame sensor as an interrupt source and enables events (interrupts), then goes into a tight loop. When the flame sensor detects UV light the program jumps to the "event landing" and plays a sound. This program only detects the first pulse from the sensor and then stops. The program uses the default settings for the "light sensor event" block. (Port 1, red event, trigger value is 55).
A small tea candle 1 meter away will generate about 15 pulses in 5 seconds. The same candle at 2 meters will generate around 8 pulses in 5 seconds. Maximum detecting distance of a cigarette lighter is about 5 meters.
Inside the glass tube a 350 volt potential exists between the metal plate and the curved wire. When UV light hits the metal plate electrons are released. The electrons are accelerated toward the wire. As they travel they strike gas molecules and ionize the gas, releasing more electrons. The process grows quickly until much of the gas is ionized. The ion/electron mixture conducts electricity and discharges a small capacitor, causing the current to fall below what is needed to maintain ionization. The tube can not “fire” again until the capacitor recharges to about 280 volts. This takes aprox. 50 mS.
When the tube discharges it creates a pulse that is filtered through a counting circuit. If the circuit has seen 3 pulses in the last two seconds, the pulse is passed through. Otherwise, the pulse is blocked. This prevents false