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Electrical Design
Our Circuits
Every circuit was assembled, soldered and debugged by each team member. General board layout was planned as a group while exact placement was left up to personal discretion.
The following circuits were located on wide PCB's, dubbed 'Natasha' boards:
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2 H-bridges, which enabled direction reversal of main driving wheels. Compact IC's were not used - as a learning opportunity, these circuits were built from individual components
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2 Optoisolators to communicate with the microcontroller
The following circuits were connected to broad PCB's, dubbed 'Boris' boards:
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STM32 'Blue Pill' microcontroller
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Sonar sensor to detect aluminum cans
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3 Optoisolators to protect microcontroller and issue commands to servo motors
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2 Schmitt Trigger circuits to allow incremental registering of mechanical switches
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Potentiometers for PID tuning, allowing for quick and convenient adjustment
tape sensor circuit
tape sensor on robot
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tape sensor circuit
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On the underside of the robot, reflectance sensor circuits were used for tape following
EMI Considerations
Board architecture relied heavily on noise considerations throughout the project. Various techniques our team used to mitigate potential issues are described below:
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Sensitive control circuitry was isolated on the 'Boris' board while "noisier" circuits were placed on the 'Natasha' board
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Optoisolators were used when the microcontroller interfaced with DC or servo motors
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A faraday cage was built to house control circuitry - a layer of aluminum foil was used as the cage and was placed in-between construction paper to minimize the risk of a short circuit
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Shielded cables protected all outgoing control connections from the 'Boris' board, i.e., tape sensor, sonar, and H-bridge control circuits
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Lengths of all connective wires were reduced to decrease inherent resistance
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Assorted decoupling capacitors
shielded cable
open faraday cage + Boris board
shielded cable
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Design Awareness
Initial battery selection
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Our team performed current draw tests to select the number of 9V batteries to optimize battery life and robot weight
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Current draw from the SG-90 and MG996R Servo Motors were found under various loads, yielding the graphs below
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The number of 9V batteries (3) were selected using a Voltage vs Service Life graph taken from it's datasheet, provided by Duracell
Rechargeable AA batteries
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Most of our members adopted AA rechargeable batteries during testing and integration, to achieve greater current output than 9V's and ultimately reduce waste
Servo - Current vs Applied Load
Duracell 9V - Voltage vs Life
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