ELECTRICAL SCHEMATICS OVERVIEW
All Created and Edited using Eagle CAD
( click to zoom in all images)
LASER EMITTER
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Our theme of our arcade game is an alien shooter. In keeping with our theme we decided to use a laser to mimic the classic space weapons used against the "aliens". The KY-008 is the one we picked to mount our turret. The 650 nm wavelength is perfect for our photoresistor. The design specifications required us build an arcade that was at least 3 feet in length. We needed our laser module to cover this length, which when we looked at the datasheet it easily covers up to 60 feet. Safety is a priority in our game, so we locked the turrets maximum direction to implement a hard stop so the players aren't able to point the laser directly at themselves.
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LIGHT DETECTOR
(SENSOR)
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For our sensors we had several options in our Arduino Mega kit. One of those options was using an IR receiver and emitter combination. These sensors detect infrared light being emitted from the IR emitter. The issue we had at hand was the way we wanted our game to play. Our theme is an alien space shooter so we wanted to visibly see something shooting out from our turret. Another problem we had was that we were going to implement a moving target( UFO Spacecraft), we needed a type of sensor that can detect light at any angle.
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We decided in using a photo-resistor for our targets. These work by light detection. Naturally these photo-resistors work by changing it's resistance with the amount of light received. Since we are using a laser module (KY-008) we want this to lower it's resistance to supply current to an LED; LED will trigger and light up. With its peak response roughly matching the laser 650 nm wavelength, this sensor is ideal. Throughout our tests and many nights of debugging we measured how much voltage was dropped across the photo-resistors. Starting at ranges from 0 ft we see no voltage dropped. From time to time we can see very small voltages dropped due to noise coming in from external light sources such as sunlight. In ranges from less than 10 feet we see voltage drops of around .750 volts when triggered. This voltage drop is lowered by a bit as we increase distance but it's still constant at distances up to 5 feet.
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Since the photo-resistor is light activated, having just an LED connected to it directly has an issue of lighting up directly in proportional to how much light is being captured by the photo-resistor. For an LED to fully brighten we need at least a constant input of 10mA. We've tried using no BJT transistor as a set up with the results lacking. The LED would certainly be dimmed if the laser wasn't held in place for a brief time. The point of this game would be to shoot the target and to quickly see an LED turn on or remain off. This setup would not work for our conditions.
The use of a transistor gives us the capability of switching the LED on and off depending on photo-resistor detecting light. This was our fix to our LED lighting brightly or dimly depending on the strength of the light coming from the laser module. 2N3904 BJT transistor are usually used to amplify analog signals. Due the photo-resistor being analog in nature we need to be able to amplify the signal being received from our laser module to then activate the LED like a switch. A buzzer was also implemented for hearing stimulation type of element. Just seeing light and motion of the target falling doesn't excite a player as much as hearing some noise along with it. The buzzer works in software where once the LED is triggered it sends a signal to the buzzer to also trigger at the same time. There wasn't any lag from light to buzzer, which was aided by the use of the transistor.
A lot of testing was done using this setup. A few issues that can affect the overall performance of this sensor is that it can pick up a lot of noise from external light sources, sometimes even setting off the LED/Buzzer combination. If we had an opportunity to build the arcade cabinet we would paint it black to lessen the amount of external light that can cause this issue. This would also add to our theme of feeling in space. Overall this setup was a better way to help us implement our shoot and activate style of gameplay.
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TURRET
The turret system acutated using two 28BYJ-48 stepper motors. Motor sizing analysis was not performed for this subsystem since it was it rig-tested with positive results. Important specs needed from the datasheet include:
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- 4-Phase Motor
- Rated Voltage: 5 VDC
- Speed Variation (Gear) Ratio: 1/64
- Stride Angle: 5.625 deg/64
- In-traction Torque: 34.3 mN*m
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The two motors are Pulse-Width-Modulated driven by ULN2003A Darlington array transistor boards which include flyback diodes for switching inductive loads. Specs:
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- Max. Current: 500 mA / Output
- Supply Input: 12-6 V
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Motors are connected with a capacitor to prevent inductive spikes.
Since motors require a lot of power to run, the system is powered by two possible optiions:
- Li ion or Pb power banks 10,000+ mAh batteries
- Automobile battery with a buck converter.
* Not implemented due to COVID-19 but worth mentioning since it was part of the design requirements.
TARGETS
(MOVING AND STATIC)
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For the moving target, mechanical calculations required a motor capable of 0.309 N*m of torque or 300 mW of power. Since the mechanism required motion to be locked in order to avoid collisions with the enclosing structure, Servo motors are the ideal choice because the are self contained units with a driver and an encoder.
The affordable 55g servo motors from SunFounder were found to be more than capable of meeting said requirements. We calculated its output using its datasheet data to be:
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- Max. Mechanical output: ~1.5 N*m
- Max. Power output: ~9 Watts
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For the Static Target, due to a team member dropping out and lack of time, motor calculations were skipped which lead to the motor not being able to handle the designed load. *see mechanical section for solution. Motor utilized is 9g SG90 servo.
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We have decided to breakup the turret and wiring it up on a separate Arduino due to the amount of pins required to run the stepper motors. The second Arduino will handle the control panel, sensors and target systems. Here we have the schematic for our moving and static targets. In our static target we have one servo with an alien cutout (initially we wanted 3D printed) mounted on the servo. In code when the photo-resistor is triggered the servo will drop down in a 90 degree motion. The buzzer and light is activated as well to show the alien has been hit. We have a 470uF capacitor to protect our Arduino in case of any current surges generated by the servo.
Our moving target works in a similar way but we have used two servos. These two servos are linked by an arm. One of the servos controls the arm connected at the base of the moving target, while the other controls the alien ship mounted on second arm.
CONTROL PANEL
The control panel is part of our second Arduino Mega subsystem. The 16x2 LCD display outputs important information pertaining to our arcade game. It outputs information such as: game timer, swipes detected and score tracker. We also see how our swiper sensor is built. Here we have used a pair of IR emitter and receiver. To start our game we slide a card across the IR emitter/receiver combination which breaks the IR path created by this combination. This is then counted on our LCD display as a swipe and initializes our game.
BLOCK DIAGRAM
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BOM
Built of Material
