Our PAC required a number of circuits in order to achieve full functionality. To show you how we did it, we've detailed our circuits below for each piece of functionality.
Pinout Diagram
Power Distribution
powerdistributionpac.pdf | |
File Size: | 82 kb |
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Two in-parallel 7.2V NiMH batteries provides the power to the PAC. A 10A fuse is used to guard against overdrawing current, and a SPST switch is used as the master kill switch. A XL2596S buck converter is used to step the 7.2V of batteries down to 5V. This 5V power line is used to power most electronics in the PAC.
Pair/Unpair
cap1188.pdf | |
File Size: | 64 kb |
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Pairing and unpairing commands were detected by touching the magic lamp on top of the PAC. Touches of the magic lamp were measured as a change in capacitance of an electrode inside the magic lamp. The CAP1188 sensor was used for determining when touch events occurred and relayed these events to the TIV via I2C.
Team Color Select
colorselect.pdf | |
File Size: | 37 kb |
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The Color Select circuit is comprised of a single pole, double throw switch. The common connection is connected to TIVA pin PB6. One switching connections is connected to 5 V, while the other is connected to ground. Thus, when the switch pulls the TIVA pin high, the TIVA will transmit all messages as one color (ie: red), and when the switch pulls the TIVA pin low, the TIVA will transmit messages as the other color (ie: blue).
Brake
brake.pdf | |
File Size: | 34 kb |
File Type: |
For the brake button, TIVA pin PB4 will read a high value when the LOBBYIST is operating normally. When the user wants the LOBBYIST to brake, a push button will pull the pin low, signaling the PAC to communicate to the LOBBYIST to brake.
Team Select
player_select.pdf | |
File Size: | 53 kb |
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A 12 position, single pole rotary switch without a stop is used on the PAC to select the LOBBYIST number that the user would like to pair with. Every 3 consecutive pin connections are shorted together, essentially creating a single pole, quadruple throw rotary switch. Each circuit represents one of the active players.
The TIVA pin for each individual player circuit is pulled high using the internal TIVA pull-up resistors. When selected by the rotary switch (which is connected to ground), the pin of the desired player is driven to a low state.
The TIVA pin for each individual player circuit is pulled high using the internal TIVA pull-up resistors. When selected by the rotary switch (which is connected to ground), the pin of the desired player is driven to a low state.
Special Action
ir.pdf | |
File Size: | 195 kb |
File Type: |
A simple IR transmitter/receiver circuit is used to detect the special action (sword swing). Under normal circumstances, the IR signal is recognized by the receiver. When the sword is swung in the PAC, the IR signal is blocked, which is processed by TIVA pin PE0.
The IR receiver contains a high-pass filter (centered at 2.5V) after the initial amplification. This is used to eliminate the DC offset that occurs from ambient light. A 500k potentiometer was used to adjust and tune the corner frequency of the filter.
A 74HCT14 inverting schmitt trigger is placed after the high pass filter in order to create a binary signal that is unaffected by noise.
The IR receiver contains a high-pass filter (centered at 2.5V) after the initial amplification. This is used to eliminate the DC offset that occurs from ambient light. A 500k potentiometer was used to adjust and tune the corner frequency of the filter.
A 74HCT14 inverting schmitt trigger is placed after the high pass filter in order to create a binary signal that is unaffected by noise.
Audio
wav_trigger.pdf | |
File Size: | 69 kb |
File Type: |
The WAV Trigger is a polyphonic audio player and amplifier. It was programmed by unidirectional UART communication to play background music while the PAC was powered and occasionally played sound effects in response to user inputs.
Thrust/Direction Sensing
accelerometer.pdf | |
File Size: | 420 kb |
File Type: |
The x- and y-axis accelerometers of an analog 3-axis accelerometer are used to determine the thrust and direction. Tilt in the x-axis determines the amount of direction change, while the y-axis determines the amount of thrust. In order to eliminate the high frequency noise from the accelerometer signal, a low-pass filter is placed directly after the accelerometer output. Since we are sending signals at a frequency of 5 Hz, the corner frequency of the low pass is placed at around 10 Hz.
The zero tilt offset from the y-axis accelerometer is negligible. Thus, since the peak-to-peak amplitude of the tilt signal is approximately 0.1 V, an MCP6294 op-amp is used to create a non-inverting amplification circuit with a gain of 28.
The zero tilt offset from the x-axis accelerometer is approximately 0.05 V. Therefore, in order to ensure that the amplified signal remains somewhat close to 1.65 V, the MCP6294 amplification circuit has a gain of approximately 10. Additional amplification is added in software in order to compensate for the smaller hardware gain.
3.3k pull-down resistors are placed close to the TIVA inputs. This helped reduce capacitive noise.
All electronics in this circuit are powered off of a 3.3V line that is created by an LP2950-3.3 linear regulator.
The zero tilt offset from the y-axis accelerometer is negligible. Thus, since the peak-to-peak amplitude of the tilt signal is approximately 0.1 V, an MCP6294 op-amp is used to create a non-inverting amplification circuit with a gain of 28.
The zero tilt offset from the x-axis accelerometer is approximately 0.05 V. Therefore, in order to ensure that the amplified signal remains somewhat close to 1.65 V, the MCP6294 amplification circuit has a gain of approximately 10. Additional amplification is added in software in order to compensate for the smaller hardware gain.
3.3k pull-down resistors are placed close to the TIVA inputs. This helped reduce capacitive noise.
All electronics in this circuit are powered off of a 3.3V line that is created by an LP2950-3.3 linear regulator.
Wireless Communication
pac_xbee.pdf | |
File Size: | 89 kb |
File Type: |
A Digi XBee was used for radio communication. The Tiva interfaces with the XBee using API UART communication.