Electronics
This section takes you through assembly of the electronics of the ROV. Have a look at the electronics components and make sure that you have all of them present. This tutorial will not give detailed instructions on how to solder or how the various components work, feel free to research that on your own. The goal is to show the various steps required to complete the ROV-build.
The circuit design and PCB layout has been done in an open-source program called KiCAD, read more about it here if you are curious or want to try something like this for yourself.
The schematics can be downloaded as pdf documents from the bottom of this page. You can have a look at the PCB-layout from this picture. The green/yellow field on the circuit is a +Vbat zone, and the red field is the GND zone on the top of the PCB.
PCB soldering - Begin with this
end up with this
Components
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Big blue PCB
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Arduino Micro
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11 x 10k Ohm resistors
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8 x 10 Ohm resistors
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7 x 2-pin screw connectors
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2 x 3-pin screw connectors
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2 x IC sockets
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2 x Darlignton transistor arrays
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2 x 17-pin female headers
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16 x Diodes
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8 x Relays
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1 x Mosfet
Tools
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Soldering iron
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Solder
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Small flat wire cutters
Nice to have:
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Tip cleaner/brass sponge
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Helping hands
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Tape or putty
Procedure
If you have never soldered before, I suggest heading over to YouTube for some some video tutorials. For example this one. Pay attention to the details written on the board. It indicates the direction of the screw connectors for example.
General tips:
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Always clean the tip of the soldering iron regularly
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Heat for ca 1 second and apply a small dab of solder
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Start populating the PCB with the smallest components, so they stay in place if you flip the board over
Wire harness - Routing the power
Components
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Battery connector
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Fuse holder
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20A fuse
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Somewhat thick black wire
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5V UBEC
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Micro-USB cable
Tools
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Soldering iron
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Solder
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Wire stripper
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Heat shrink tubing
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Battery connector
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Wire cutters
Nice to have:
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Tip cleaner/brass sponge
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Helping hands
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Procedure
What we are doing here is basically only connecting the battery to the PCB with a wire. In addition we are converting the battery voltage down to 5V for the Raspberry Pi. The Micro-USB cable is routed down through the little hole in the board to power the Pi.
I like to tin the wire ends before I stick them in the screw connectors, so they don't separate and cause short circuits. Here we are also splicing two wires into each screw connector, to make room for them all I cut away some of the strands in the wire from the fuse holder. About half as many should be fine, as the wire is somewhat thicker than what we need anyway.
You may also have to change the connector on the battery. Be careful! These batteries can deliver quite a lot of power, only cut one wire at a time, and never have both battery wires stripped of insulation at the same time
Auxilary parts - Temp sensor, pressure sensor and front lights
Components
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Pressure sensor - MPX4250
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Temperature sensor - LM35
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16 x White LED's
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8 x 75 Ohm resistors
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Prototyping board
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Black and Red wire
Tools
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Soldering iron
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Solder
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Small flat wire cutters
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Glue gun
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Utility knife
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Heat shrink tubing
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Epoxy glue
Nice to have:
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Tip cleaner/brass sponge
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Helping hands
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Tape or putty
Procedure
The front lights are wired up as shown on the schematic, make sure you keep track of the polarity of the LED's. The long leg goes to positive voltage.
Cut out pieces of the prototyping board with 7 x 13 holes. Score along the 9th and 15th rows of holes with the utility knife and break the board along the line. Then procedure to solder it together according to the schematics.
The temperature sensor and pressure sensor we are preparing here, are the ones that will measure the temperature and pressure in the water outside the ROV. However, only the temperature sensor will go outside of the hull and into the water, the pressure is measured through a small tube that sticks through the wall of the ROV. Since the temperature sensor will become wet, we coat it in epoxy for protection!
The wiring of the sensors is quite simple; 5V, ground and a signal wire. In the pictures, the signal is the white wire.
Google the sensors for their pinout details
Threading the wires
Components
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Almost finished ROV
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Motors mounted
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PCB finished
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Sensors prepared
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Electronics mounting board with Pi installed
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Ethernet cable
Tools
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Soldering iron
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Solder
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Small flat wire cutters
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Wire stripper
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Glue-gun
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Permanent marker
Nice to have:
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Tip cleaner/brass sponge
Procedure
Start by measuring up how long the motor wires and ethernet cable needs to be in order to reach their desired locations without too much to spare on the outside. Mark the position on the wires where they should be in relation to the wire-throughs in the hull.
Glue them in place, and start filling the tube with hot-glue a little at a time. Too much at once and it will just be dripping out and making a mess.
Wiring up the motherboard
Components
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Finished motherboard
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Finished headlights
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Prepared sensors (temperature and pressure)
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Motors and cables glued in place
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Micro-USB cable
Tools
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Soldering iron
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Solder
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Wire strippers
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Small flat wire cutters
Nice to have:
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Tip cleaner/brass sponge
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Glue gun
Procedure
Connect the micro-USB cable between the Raspberry Pi and the Arduino, it might be easier to route nicely if you wait with connecting it to the Arduino.
Measure the required length of wire from the sensors, then; cut, strip and tin the wires before you screw them in place. Do the same with the motor wires. Since the different motor-control channels already are defined in the Arduino code, it's easiest for everyone if we stay with those definitions, they are as follows:
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Channel 1 and 2: Rise/dive motors these work together, so where they go doesn't matter)
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Channel 3: Port side motor, that's on the left side if you are facing the rear of the boat
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Channel 4: Starboard side motor. Well, it's the only one left anyway
If the motors spin the wrong way when you test them, just reverse the polarity of the motors. I.e, change the two wires around.
When mounting the front lights, there are several different options; they can be placed underneath the board, on each side of the camera, on top of the board as I have done here or in the lid of the hull, just make sure they don't crash into anything when you close the ROV-lid.
Design files
The ROV circuitry features a custom motor-controller setup, which is currently undergoing some serious rework. You can find the currently used schematic and PCB-layout here.
The motor controller is based on relays, in order to keep the electrical system as easy to understand as possible. The major disadvantage with this choice is that we only have ON/OFF control of the DC motors. Which makes the control less smooth. This is however a feature which is perfect as a DIY modification to the ROV.
The circuitry design is done using KiCAD - a free design tool for the job.