This year, the electrical team’s main focus was to integrate all of the dependable systems from AquaUrsa onto Auri, along with a multitude of upgrades. Since Auri is much smaller, revisions have compensated for this change in size without sacrificing overall performance. Additionally, Auri is now equipped with an array of voltage measuring devices and environment sensors such that Auri’s health can always be monitored. Some of the main projects completed this year include: an upgraded power board to supply all of the electronics inside the hull, hydrophone filtering and amplification to be used for sonar, an improved actuator control board, battery and voltage monitoring circuits, internal environment sensors and a simplified motor board, just to name a few. Auri was designed with modulation and future advancement in mind, where all of the essential circuit boards come with additional room for expansion. This allows the easy addition and removal of peripheral systems, so that Auri is always prepared for the next big challenge.
The new power regulation board was meant to be a near drop-in replacement the board used in AquaUrsa, meaning that it needed to supply power on 12V, 5V, and 3.3V rails and it needed to be controllable using a single pole remote switch. Beyond those specifications, the design of the new board began to deviate from that of the old board to reflect new or upcoming robotic requirements. This included higher power output, especially on the 5V and 3.3V rails. Other requirements included reverse input voltage polarity protection and current sensing.
The battery monitoring system is designed to monitor the voltages of the four batteries powering the robot and display them on an LCD in real time. The main system is incorporated into the power board; however, the LCD and a hall sensor are separate. The system uses two INA3221s to monitor the voltages of the batteries and the current from the motors. Each of the INA3221s can monitor up to three channels and detect load voltage, bus voltage, and current from each channel using small current sensing resistors. The INA3221s have several warning features such as power-valid, warning, and critical that are active based on the voltages measured. These features have not yet been coded or tested, but the wiring is there for future use. The system uses a teensy 3.2 to run the INA3221s, a standard 16x2 LCD, a shift register, and a hall sensor. The teensy was chosen due to its small size, low cost, and compatibility with Arduino software. To reduce the number of LCD pins required on the teensy from six to three, a 74HC595N shift register was added to the board. To conserve power, the backlight of the LCD can be switched on and off using a DRV5033 digital omnipolar hall switch which will be mounted near the outside of the hull. In summary, the INA3221s measure the voltage and current values which are collected by the teensy. This data can be used by the software team to determine exactly when voltage or current drops occur. The teensy also sends the voltage data to the LCD mounted next to the hull which displays the values when a magnet is present near the hall sensor.
HoneyWell’s HIH7120 is a dual humidity and temperature sensor the purpose of which is to monitor humidity of the air inside the hull to possibly detect leaks and prevent equipment failures. The temperature sensor will be used to detect the internal temperature of the submarine so that equipment failure due to overheating may be avoided. This sensor was the best choice for several reasons including its digital output. The sensor outputs the data over I2C after the master device sends a measurement request otherwise the sensor is in a low power mode which conserves energy. The sensor also has an unlimited moisture sensitivity level meaning that the sensor won’t have to be replaced very often. This sensor also boasts a fast response time which will allow the submarine’s computer to dynamically monitor the humidity levels and be able respond quickly given a rapid change in the internal environment. While the sensor isn’t the most accurate, for the purposes of detecting a change in humidity it will work fine. Furthermore, the sensor’s small size will allow for it to be integrated into a smaller pcb conserving valuable space in the inside of the submarine. Finally, the sensor’s relatively low cost will be a benefit if the circuitry is damaged or more than one sensor is needed, inside the quad or for going through prototypes of the board as soldering the sensor to the board is tricky due to its small size.
NXP MPL3115A2 is a dual pressure and temperature sensor. The pressure sensor is an absolute piezoresistive sensor, the purpose of which is to monitor the pressure inside the hull for any sudden changes which would indicate a hull breach or failure. This sensor was chosen also because if it’s digital I2C interface. This allows it to be directly interfaced with a microcontroller making the pcb design smaller and more compact. Next the sensor is quite accurate and has a quick response time allowing for the internal pressure to be dynamically monitored at a high degree of accuracy. This will allow the detection of minor changes in the pressure very quickly and allow the submarine to detect possible hull failures. This sensor is also quite small and low powering which offers the same advantages as described for the humidity sensor. Finally, the sensor is even lower cost than the humidity sensor allowing for multiple sensor to be purchase for multiple measurements prototypes and replacements.
The actuator board of Auri was designed to control all output devices on the robot other than the thrusters and motors. It features a Teensy 3.2 microcontroller that receives instructions from the ODROID via the microUSB port, and its GPIO pins control different components in the board. The board takes power inputs of 5V and 12V from the power board.
Two servo motors (left and right) are controlled independently by PWM output pins from the Teensy 3.2, to set the angle, and the board also supplies 5V power to each servo motor.
Circuitry was designed to provide power to two independent 12V 1A solenoids, one for each torpedo, when needed. A BUK9K6R2-40E,115 IC (MOSFET 2N-CH 40V 40A), was used for switching power to the solenoids ON/OFF. This IC was chosen due to the high amount of power needed by the solenoids. 1N4007 diodes were used to protect against voltage spikes when power to the solenoid was switched from ON to OFF.
The board also features ON/OFF control for three independent LED strips, through the use of three VN3205N3-G-ND MOSFETs.