The Electronics Tube is the central “brain” for the AUV. The electronics tube can be broken into several subsystems: the PC/104, Data Acquisition Card (DAC), Wireless Card, Power Management Board, Relays, and DC/DC Converters. The electronics are mounted directly to the Subconn end cap via 3 PCB plastic squares and 4 threaded rods. Each plastic layer can be adjusted to house a variety of components.
The PC/104 was purchased new this year from Versalogic Corporation. The EPM-CPU-10 was chosen with a Pentium III/Celeron processor module with 10/100 Ethernet, Video, and PC/104-Plus interface. Unlike the PC/104 used in Gamera, the Versalogic model contains a built in I/O port, in the form of a detachable ribbon. The CPU can run at 566MHz, but is currently throttled to 350MHz do to heat dissipation considerations.
The system contains 256 MB of low power system RAM that is supported in a high-reliability latching 144-pin SODIMM socket. The PC/104 contains one PCI-based IDE channel, with a 40-pin interface. This is capable of supporting up to two IDE devices (hard drives, CD-ROM, etc.). Currently, the device is attached to an IBM 1GB Micro Drive.
JS2 (marked on board) is available for SVGA display used for debugging or setting up the computer. At all other times, the user can remotely log into the PC/104 via the wireless card.
JS4 connects to the breakout ribbon cable with the following I/O connections:
| Port | Current Use |
| RS-232 Serial Port COM1 | DVL |
| RS-232 Serial Port COM2 | Acoustics |
| Parallel Port | Unused |
| USB Port 1 | Web Camera 1 (Downward Facing) |
| USB Port 2 | Web Camera 2 (Forward Facing) |
| AT Keyboard Port | Keyboard as needed |
| PS/2 Mouse Port | Unused |
| IDE Data LED & Programmable LED | Hard Drive Activitiy / Programmable LED unused |
| Ethernet Port | Connected for Floating Wireless as needed |
The team has two I/O cables for the PC/104. One of them contains the bare essentials necessary for the competition (to remove excess wires) while the other is unaltered and used for testing and debugging (when the keyboard, etc are necessary).
The PC/104 has a custom power connector that contains the following inputs: Ground, +5VDC, +12VDC, -12VDC, and +3.3VDC (currently unused). Should the connector become damaged, the linked pdf file contains the wiring directions for the PC/104.
The DAC is a PC/104 compatible card that resides between the between the PC1/04 and Wireless Card. The DAC is model MM-32-AT made by Diamond Systems. The DAC has two sets of output pins on opposite sides. The larger of the array is the analog output, and the smaller is the digital output. The DAC card is essential to several components of the AUV, as it provides a means of analog communication between the PC/104 and non-standard systems. The digital portion of the DAC is used less frequently, and is usually used to trigger relays.
There are 4 analog output pins on the DAC and 32 analog inputs. The inputs can be configured (using jumpers) as 32 single-ended, 16 differential, or 16 SE + 8 DI with 16-bit resolution. A single-ended input is a single-wire input that is measured with reference to the board’s analog ground. A differential input is a two-wire input that is measured by subtracting the low input from the high input. This type of connection offers two advantages: It allows for greater noise immunity, and it allows for the signal to float away from the board’s ground. Both the input and output pins can be programmed in unipolar or bipolar mode set to input/output ranges of 0V-5V, 0V-10V, +-5V, and +-10V. For our purposes the board is set to operate in bipolar +-5V, with all inputs set to differential.
The 4 output channels on the DAC control the four Tecnadyne 250 thrusters onboard the AUV. The signal voltage from the DAC controls the amount of power (and thus thrust) to each thruster. The built in control circuitry on the Tecnadyne thrusters recognizes -5V as full reverse and +5V as full forward. Thus, by sending the thrusters a range of control voltage in the +-5V range, the computer is able to precisely control the thruster movement.
The input channels of the DAC are utilized for several purposes. Pins 31-34 are used in differential mode to read in the voltages of two lithium polymer power systems (thruster power and electronics power). A voltage divider circuit (see power board), is used to scale the output of the batteries to a readable range (between 0-5V). This is sent into the DAC where the value is scaled back in software to restore the original battery voltage. The li-po voltages are important values since they tell how much battery life remains, as well as the voltage levels supplied to the thrusters. Since this value changes over time, thruster control algorithms can be tweaked to stay stable as the thruster supply voltages drop over the course of the competition (from roughly 33V-28V).
The input channels (29-30) are also used for the pressure sensor input. The pressure sensor delivers a voltage between +0.5V and 4.5V, which is read through the DAC and converted in software to correlate with the AUV’s depth (in meters) under water.
Since all analog outputs of the DAC are utilized by the thrusters, the digital outputs of the DAC are used to trip any relays necessary in the competition. Currently, the Marker Dropper device is activated using this method. When the computer decides to drop a marker, a +5V signal is sent through the digital output, where it trips a Crydom relay. The relay allows raw voltage (from the thruster supply) to cause the droppers to retract and drop the steel balls into the targets.
The Wireless Ethernet Card is a PC/104 compatible card that lies at the bottom of the PC/104 stack. Users can telnet into the AUV using the specified login ID and password. The Wireless Card has a range of approximately 500 feet, and the card must reside outside of the water. If communication is required while the AUV is submerged, a user can logon via the Floating Wireless Card, which is a separate optional tethered communication method.
The Power Management Board has inputs for both the 30V thruster battery supply and the 30V electronics supply. The power management board distributes the raw incoming power from the 4-pin battery supply. The thruster power is distributed to each of the thrusters, and the electronics supply is delivered from the power board to the DC/DC converter inputs. In addition, the power management board has voltage divider circuitry used to output the (1/11) of the incoming voltage. The voltage step-down is required for the DAC to be able to read the voltage off the batteries, since its maximum capable input is 10VDC. The voltage is reduced on the power management board via two resistors in series linked in parallel to the raw power supply. The lines are then fed into an op-amp to deliver a low impedance signal into the DAC. The DAC has high impedance inputs, and so the signal must be low impedance for the DAC to read the signal properly. +5V and G is needed from the DC/DC power supply in order to power the op-amps on the management board.
The DC/DC board resides along the side of the electronics tube. Raw 30V power is supplied from the Power Management Board (and thus from the li-po battery tube) into the DC/DC converters.
The DC/DC converters create a floating ground and three available power supplies: +5V, +12V and -12V. These supplies remain stable even as the battery voltage decreases from the raw power supply. The DC/DC board requires between 18V and 36V to operate properly. The DC/DC board actually contains two separate DC/DC converters manufactured by Astrodyne. The FDC40-24S05 supplies the +5V supply, and the FDC40-24S12 supplies the -12V and +12V supply. The DC/DC units are mounted on a dual layer PCB custom designed board that allows multiple connections to be established to the converters.
The Duke AUV uses Subconn Low Profile Series underwater connectors to link the Battery Tube and Electronics Tube with each other and the numerous onboard sensors. The Subconn bulkhead connectors ensure full watertight seals at near full ocean depths. In addition, the quick release wet-mateble cables allow components to be unplugged and plugged into the system quickly and easily.
The Subconn connectors are rated between 10-15 Amps at 600V, allowing the thrusters and other onboard components to safely pull power from the lithium polymer batteries. In order for all the components to have the correct type of connectors, several sensors were sent to Deep Ocean Engineering to have Subconn connectors podded onto the open ended whips supplied by the sensor (DVL, etc) manufacturers. The DVL and Altimeter are podded with LP-7Pin female cable, the Pressure Sensor and Droppers are podded together into a LP-7Pin female cable, each of the Tecnadyne Thrusters contains a LP-7Pin female cable. The Battery Housing and Electronics Housing each have 4pin male bulkhead connectors linked via a LP F-F 4pin cable. In total, the Electronics Housing contains 10 LP male bulkhead connectors. The Camera Housing contains a LP-7pin bulkhead connector which is linked to the Electronics Housing via a LP F-F 7pin cable. Exact pin specifications can be found in pdf documents below.
Electronics Endcap Pin Labels
Electronics Endcap Pinout
The Duke AUV uses two Logitech QuickCams for vision-based navigation. The QuickCams are installed in a waterproof tube and connect to the Electronics tube through a Subconn cable. The cameras are interfaced with the Versalogic computer using standard USB cables. The cameras provide 640 X 480 video feed, with optional 1.3 Mega pixel still images and zoom features.
The computer is able to process about 10 frames/sec, allowing the AUV to detect interesting features even while moving at full speed through the water. One camera is downward facing in order to detect bins along the bottom of the pool. The other camera faces forward in order to detect the blue LED lights that mark off the array of bins underwater. The cameras gather and store images on the computer while the software analysis the images for shapes that signify LED sources and bins.
The Duke AUV team uses the RD Instruments Workhorse Navigator 1200kHz series for its main positioning system. The DVL uses 4 beams of sonar to measure its velocity in the water.
By integrating the velocity information, the DVL is also able to deliver XYZ position information from the DVL’s starting location. The DVL displays an abundant amount of other useful information – including compass heading, pitch, and roll. The DVL sends measurements up to 10 times a second, making navigation extremely accurate. By using the DVL as a feedback system, the Duke AUV can adjust its navigation on the fly. The DVL receives 24VDC of power from the main electronics tube. The power is provided from the +12V and -12V of the DC/DC converter. A separate Daytel DC/DC converter transforms this voltage into +24V and Ground. The DVL communicates with the PC/104 using standard RS232 communication. The power and communication wires connect to the DVL using the Duke AUV standard Subconn 7 pin connectors (see connector/pinouts for more information). Drivers have been written to communicate with the DVL using the Linux operating system. Driver and software integration can be found in the software section of this online report.
The AUV uses an onboard WL400 pressure sensor manufactured by Global Water Instrumentation to provide water pressure information. The Pressure sensor's cable is attached to a Subconn underwater connector that feeds into the electronics tube. The DC/DC converters provide the pressure sensor with +12V. The DAC reads in the input voltages from the pressure sensor (across a 250ohm resistor) and converts the voltage into a depth rating (in meters).
The pressure sensor reads 0.5V at sea level, and the output voltage rises as the sensor is submerged below the surface (reading 4.5V at 25PSI, or about 17 meters). The pressure sensor provides an essential feedback mechanism for the AUV's navigation. The onboard computer constantly reads depth information from the pressure sensor to ensure that the vehicle does not drift upward or downward as it tries to travel in the XY plane. As soon as the depth reading exceeds the specified tolerance, the center thruster will rotate and bring the vehicle to its appropriate Z coordinate position.
The Duke Robotics Team uses four 14.8V 8000mAh Lithium Polymer battery packs made by ThunderPower to supply the necessary power to the AUV. Two packs are connected in series to supply 29.6V, 8000mAh to the thrusters (System 1), and the other two packs are connected in series to supply 29.6V, 8000mAh to the Electronics Tube (System 2).
Both System 1 and System 2 enter the electronics tube through a 4 pin Low Profile Subconn Connector. System 1 is connected to the thruster input on the power board and is immediately routed back out to the thrusters. System 2 enters the power board where it is routed to the DC/DC converters (see DC/DC for more information). Both systems contain safety fuses in the battery tube before the power enters the Subconn connector. The power in System 1 is fed through an electrolytic capacitor in the battery tube in order to condition the power to the thrusters and prevent voltage spikes in the system. Extreme care should be taken when replacing the electrolytic capacitor, as connecting it in the reverse direction can cause the capacitor to heat up and eventually catch on fire.
Lithium polymer batteries provide the greatest energy density available to consumers. The batteries supply the AUV with 6-8 hours of computer use depending on the sensors attached. Typical thruster use allows the AUV to maneuver for one hour before a recharge. Care should be given when using the batteries, as draining the system below 10% (about 24V over system 1 or 2) will cause permanent damage to the batteries. The batteries must be charged with a lithium polymer compatible battery charger. Currently, the Duke AUV team uses the Orbit Microlader Charger. This charger is capable of fully charging each battery in about 4 hours.
Since wireless communication does not function through water, the AUV group has designed a floating wireless buoy that allows users to communicate with the AUV via a wireless enabled laptop. The Buoy has about 15ft of cable, allowing the user to control the AUV while the vehicle is submerged, and view the AUV’s activity in real time.
The two video feeds from the onboard cameras can be streamed to the laptop for easier navigation. Since communication during the competition is prohibited, the wireless buoy is used for testing and troubleshooting.
A D-Link Wireless Access Point Router is housed in a watertight Pelican box that floats at the surface. A 3.3Ah 5V lead acid battery powers the Router. A Waterproof Bulgen Ethernet cable provides communication between the Router and electronics tube. Any laptop with an 802.11b compatible wireless card can telnet onto the AUV.
D-Link Technical Manual
Bulgin Waterproof Ethernet Cable
The reed switch provides an emergency on/off switch that allows divers around the vehicle to easily deactivate power to the thrusters. The Duke AUV team uses the RI-80 SMD Series switch. The reed switch works as a magnetic on/off device.
When a magnetic field is placed over the switch, the reed switch flips to low resistance and allows current to flow. When the magnetic field is taken away, the switch flips to high resistance and no current is able to flow. Since the switch can only safely carry 350mA of current, the switch line does not directly interact with the thruster batteries. Instead, a 9V battery is connected in series with the reed switch, and the two open leads are placed across a Crydom relay. When the magnet is placed over the reed switch, the circuit is completed and 9 Volts drop over the relay. The 9V activates the relay, which in turn allows the positive +30V thruster power to reach the terminal blocks on the power board. The reed switch is podded inside of a 2 pin Subconn Low Profile series connector. The Subconn cable is mounted underneath the chassis against the bottom acrylic shell. A horseshoe magnet attached on the outside of the vehicle provides the magnetic field necessary to trip the reed switch.