If you’re familiar with using a compass (the tool that points to magnetic north, not the one that makes circles) the concept of holding the device level makes sense. It must be level for the needle to balance and rotate freely. You just use your eyes to make sure you’re holding the thing right. Now think of a digital compass. They work by measuring the pull of a magnetic field, and have no visual method of showing whether they’re level or not. To ensure accurate readings you might use an accelerometer to compensate for a tilted magnetometer.
The process involves taking measurements from both an accelerometer and a magnetometer, then performing calculations with that data to get a true reading. Luckily the equations have been figured out for us and we don’t need to get too deep into trigonometry. You will, however, need to use sine, cosine, and arctangent in your calculations. These should be available in your programming language of choice. Arduino (used here) makes use of the avr-libc math library to perform the calculations.
We usually avoid the prospect of buying new tools just for one project. In the long run we’re sure we’d use them again, but sometimes even with that outlook you can’t afford it. Case in point is our life-long-lust for a laser cutter; we just can’t justify the upfront cost but we sure would use it constantly if we had one.
If you do find that you’re interested in taking on a project that calls for laser cut parts, [I Heart Robotics] shows you how to do it with a few simple hand tools. The bot seen above is their TurtleBot. You can cut your own parts using a laser cutter, you can buy a kit from them, or you can bust out a ruler, compass, drill, coping saw, printer, and tape to make the pieces by hand.
It’s a simple enough concept. Print out the templates, tape them to your hard board, then start drilling and sawing. You won’t get the precision a machine tool can, but in some cases you don’t need to be all that perfect.
While some people can rely solely on memory and landmarks to find their way home, others need a bit more help. Consider Instructables user [_macke_] for instance.
Like other screenless GPS navigation devices we have seen, his “Find Home Detector” uses a GPS module to obtain his location, guiding the way home via a set of alternate indicators. In this case, he uses LEDs which are laid out like a compass rose. When [_macke_] is aimed toward his destination, the LED nearest to his fingertips lights up, letting him know he is on the right path. As he turns away from home, the other LEDs light, indicating the direction in which he should turn.
His forearm-mounted GPS navigator uses a LilyPad Arduino to control the system, much like others we have seen. It is connected to a GPS sensor and a compass module that work in concert to guide him home. The compass is responsible obtaining his heading information, and while it might look as if the LEDs that surround the module are pointing North, they are in fact indicating the heading of his destination instead.
It’s a cool little creation, and we can imagine it would be quite helpful if you happen to be walking home after a long night of drinking.
Be sure to check out the video below for a quick demonstration.
Continue reading “Forearm-mounted GPS uses LEDs to light the way home”
We’re not sure if this is the first time, but here’s some pretty solid proof that Arduino has found its way into the weapons of war. The creators, [Derek Wales], [John Eischer], and [George Hopkins] are all Electronics Engineering majors at West Point. They came up with this idea after seeing video footage of a firefight in Afghanistan where combat soldiers were calling in artillery strikes using a compasses and GPS devices. It’s an all-in-one unit that can provide the same information quickly and accurately. The prototype above, which they call the DemonEye, contains a laser range finder, digital compass, and a GPS module. The article also states that it contains a mini-computer but we recognize that as an Arduino Mega (thanks to Miguel over at Areopago 21 for noticing this first and sending in the tip about it).
The prototype apparently comes in at $1000. Okay, it seems a bit high but not out of the ballpark. What we can’t understand is how the second generation of devices was billed out at $100,000 for five more units. What’s the going rate for laying out military-grade PCBs?
[Ben Kokes] threw together a hardware package to capture data from a football. In the center of a Nerf football he made room for an accelerometer, gyroscope, and an electronic compass. All three can capture 3-axis data and, along with the LEDs ringing the circumference, they’ve controlled by an XMEGA192 microcontroller.
This makes us think back to a time when baseballs with a built-in speed sensor first hit the market… does this hack have mass marketing potential? Perhaps, but only if the $225 sensor price tag were greatly reduced. When we first started reading the description we hoped that [Ben] had coded an interpreter that would render 3D playback video from the data. He hasn’t done that, but from the data graphs he did assemble we don’t think that functionality is out of the question. We’ll keep our fingers crossed.
[eric], inspired by this Wired article, built his own haptic compass. Named “the clown belt”, it is a belt with 12 little vibrating motors mounted evenly all around. A digital compass vibrates whichever motor is closest to north at all times. This basically gives the owner an extra sense. He doesn’t go much into his own experiences, but the Wired article mentions “dreaming in north” and feeling strange once they finally removed it. Precise direction senses may not be super power worthy, but they would be cool.
In our Dev Phone 1 excitement last week, we somehow overlooked phoneWreck’s teardown of the T-Mobile G1. The complex slider mechanism is certainly worth looking out. One of the major oddities they point out is the inclusion of two vibration motors. One is mounted next to the SIM on the mainboard. While the other is mounted in the frame next to the earpiece. We wonder what was gained/solved by using two. The phone also includes a digital compass module. We’d like a more detailed explanation of how the Xilinx CPLD is used. From this article in 2006, it seems HTC uses them to generate custom clock signals and switching off devices for power management.