Firing System and Detection
Posted on Tuesday 30 October 2012
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The firing system is what the robot uses to shoot at the other robot. A robot will have one firing device and multiple targets which will detect the shots fired.
Design
The firing device will be made from a laser diode. A laser diode has a small emission angle meaning that it is very accurate. To detect the laser, a photo transistor will be used. This detects the light and converts it to an electrical signal. The laser diode and photo transistors will be connected to the Arduino, as the Arduino is very good at receiving input from a variety of sensors and also controlling emitters.
Laser Diode
The laser diode that has been chosen is the Optek Technology OPV380 Laser Diode. Below is a table of the specifications of this device along with a picture of the diode.
TABLE 1: SPECIFICATIONS OF LASER DIODE
SPECIFICATIONS
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VALUES
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FIGURE 2: OPTEK TECHNOLOGY LASER DIODE
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Wavelength
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580nm
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Current
Rating
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12mA
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Output Power
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1.5mW
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Forward
Voltage
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2.2V
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Reverse
Current
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100nA
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Maximum
Series Resistance
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55Ω
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Minimum
Series Resistance
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20Ω
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Maximum
Reverse Voltage
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5V
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Diode Case
Style
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Flat lens
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No. Of Pins
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2
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Maximum Operating Temperature
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85°C
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Minimum Operating Temperature
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0°C
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Beam Divergence
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20°
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Laser Class
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1M
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This laser was chosen as it requires very low drive currents to obtain the same amount of output power as LEDs. This feature allows the laser diode to be used in low power consumption applications such as battery operated equipment, which makes it perfect for use in the robot. The price of this laser diode is £6.99.
Phototransistor
To detect this laser diode, the Optek Technology OP550A phototransistor has been chosen. It consists of NPN silicon phototransistors moulded in clear epoxy packages. It has a wide receiving angle that provides relatively even reception over a large area. Below is a table of specifications and a picture of the phototransistor.
TABLE 2: SPECIFICATIONS OF PHOTOTRANSISTOR
SPECIFICATIONS
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VALUES
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Figure 3:
Optek Technology Phototransistor
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Wavelength
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935nm
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Power Consumption
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100mW
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Power Dissipation
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100mW
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Collector Emitter Voltage
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0.4V
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Current
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2.55mA
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Dark Current
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100nA
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Voltage
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5V
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Nom Sensitivity @ mW/cm2
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2.55mA @
1mW/cm2
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Transistor Type
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NPN
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Maximum Operating Temperature
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100°C
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Minimum Operating Temperature
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-40°C
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External
Depth
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2.28mm
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External
Length/Height
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5.71mm
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External
Width
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4.45mm
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Package/Case
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Side
Emitting
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The phototransistor is priced at £0.64, making it very cheap to buy several to have different targets across the robot.
Other Design Options Considered
Infra-red emitters were considered instead of the laser. An infra-red emitter is a lot cheaper than a laser. However, the beam from an infra-red emitter is not as accurate, and cannot be seen so that the user can aim. A laser can be seen and therefore aimed at a target. Also, the laser diode that was chosen uses a much lower drive current than infra-red LEDs.
Projectiles were also considered to be the firing device but were disregarded due to their complexity to construct and detect electronically.
