Over the past few days, I've spent a fair amount of time assembling the circuit boards for the StIRLing test bed. I now have a complete sensor shield and an almost complete power and control board. The next steps involve testing the boards and mounting them to the robot.
Sensor Shield
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The sensor shield (shown the with accelerometer,
gyro sensor, and magnetometer installed) |
The sensor shield mounts on top of the Arduino Mega, providing connections to all of the various sensors and electrical equipment on the robot. This shield includes headers for an accelerometer, gyro sensor, magnetometer, force sensitive resistors (FSRs), and ambient light sensors. The shield also includes ports for the jumper wires between the sensor shield and the power and control board.
This board took around three hours to solder together. It is simply an Arduino Mega prototyping shield with all of the necessary headers soldered on, with the idea of providing an easier method of (dis)connecting sensors and other equipment. The board also has built in resistors for the headlights and FSRs, simplifying the wiring process.
Despite the utility provided by this design, there are a few significant issues. One of which is the large amount of exposed wiring on the underside of the shield. This was necessary in order to provide power to all of the components attached to the shield. The original prototype shield lacked power busses, and my solution involved stripping a length of wire and soldering it to the +5v (or GND) terminals and another, unallocated, location on the shield. This works (I haven't had any issues so far), but it seems like a really primitive solution.
Another issue is the difficulty in producing this board, this board took about three hours to solder and some creative wiring solutions were required in order to make all the necessary connections. One of these wiring solutions involves having wire stick out the side of the shield, being routed around the pins the shield uses to attach to the Arduino Mega. This has the effect of making the shield fit somewhat poorly. I plan to avoid these issues by creating my own circuit board layout and making a custom board, but this will take time that I currently lack. Future versions of the StIRLing Platform will include custom sensor shields.
Power and Control Board
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The Power and Control Board (shown with the servo
controllers, relay and USB power adapter installed) |
The power and control board handles all of the power supply and servo control needs of the StIRLing platform test bed's electronics. It is almost complete, but lacks a few parts that I didn't own when I soldered the board together. This board provides connections to a tether and battery as well as a voltage regulator on 5v USB power adapter. These components are wired up in order to supply the Raspberry Pi with 5v (through a USB adapter with the aim of stabilizing the power output) and supply the Arduino with 7.2-7.5v (depending on the power supply in use).
This board is simply a prototype board with all of the components soldered in a very compact fashion. I originally intended for the this board to mount on top of the sensor shield, but I decided against this for a number of reasons (the prototype board I had on hand was too small to function as a shield, a lacked right-angled headers, etc.). Instead, this board will likely be mounted on its side, next to the Arduino.
This board took about three hours to solder together, with some of the soldering proving to be more difficult than it was on the sensor shield. As I had a relatively small prototype board, I had to be very efficient when packing the board. The result is a very densely-packed circuit board with more than a few soldering mistakes on the other side.
In future versions of the StIRLing Platform, this board will definitely be replaced by a custom circuit board, likely in the form of a shield. This board was assembled with a fair amount of difficulty, as it was not assembled in ideal conditions (small prototype board, missing parts, etc.). So far, this board looks okay (no accidental connections), but it has not been fully tested yet.
Overall
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The StIRLing test bed so far, with electronics in position. |
Both boards will work for now, but should be replaced by custom-etched PCBs in future versions of the StIRLing platform. In their current configuration, the boards take up a fair amount of space on the robot, but future versions will likely improve this. For now, these boards will suffice, allowing testing and software production to proceed, after a few more tests and improvements.