Building A GPS Receiver From The Ground Up

One of the more interesting facets of GPS is that, at least from the receiver’s point-of-view, it’s a fairly passive system. All of the information beamed down from the satellites is out in the ether, all the time, free for anyone on the planet to receive and use as they see fit. Of course you need to go out and buy a receiver or, alternatively, possess a certain amount of knowledge to build a circuit that can take those signals and convert them into something usable. Luckily, [leaning_tower] has the required knowledge and demonstrates it with this DIY GPS receiver.

This receiver consists of five separate circuit boards, all performing their own function. The first, a mixer board, receives the signal via an active antenna and converts it to a lower frequency. From there it goes to a second mixer and correlation board to compare the signal to a local reference, then a signal processing board that looks at this intermediate frequency signal to make sense of the data its seeing. Finally, an FPGA interfacing board ties everything together and decodes the information into a usable form.

Dealing with weak signals like this has its own set of challenges, as [leaning_tower] found out. The crystal oscillator had to be decapped and modified to keep from interfering with the GPS radio since they operated on similar frequencies. Even after ironing out all the kinks, the circuit takes a little bit of time to lock on to a specific satellite but with a second GPS unit for checking and a few weeks of troubleshooting, the homebrew receiver is up and running. It’s an impressive and incredibly detailed piece of work which is usually the case with sensitive radio equipment like GPS. Here’s another one built on a Raspberry Pi with 12 channels and a pretty high accuracy.

Designing A PCB GPS Antenna From Scratch

These days, when it comes to GPS devices the antenna is typically part of the package. But what better opportunity for [Pepijn] to learn how to make a GPS antenna from scratch for a badge add-on?

A patch antenna is an antenna of a flat design, which [Pepijn] was going to put directly on a PCB. However, there was added complexity due to GPS being a circularly polarized signal, and that meant doing some research.

Sadly, nowhere did [Pepijn] encounter a straightforward reference design or examples, but in the end success came from going with a truncated corner patch antenna design and using simulation software to figure out exactly what dimensions were needed. (The openEMS free simulation software didn’t bring success, but the non-free Sonnet with a trial license did the trick.) The resulting PCB may not look particularly complex, but every detail matters in such designs.

KiCad handled the PCB CAD design but the prototype came from cutting the PCB on a CNC machine instead of having it fabricated and shipped; a much cheaper and faster option for those with access to the right tools. A bit more testing had the prototype looking good, but the real proof came when it successfully received GPS signals and spewed valid NMEA messages. The design files are on GitHub but as [Pepijn] says, the project was about the journey more than anything else.

Ordering Pizza While Racing

As [Matt Stele] prepared to bike a local 300-mile (~480km) race in addition to training, he had to prepare for food. A full day of riding was ahead on gravel trails, and one of the best options for him was Casey’s General Store pizza. However, as it was a race, other riders were much faster than him. So, all the hot slices were gone when he arrived. With the help of a serverless GPS tracker, some cloud lambdas, and some good old-fashioned web scraping, [Matt] had a system that could order him a fresh pizza at the precise moment he needed. Continue reading “Ordering Pizza While Racing”

Mapping The Depths With An Autonomous Solar Boat

Ever look out at a pond, stream, or river, and wonder how deep it is? For large bodies of water that are considered navigable, it’s easy enough to pull up a chart and find out. But what if there’s no public data for the area you’re interested in?

Well, you could spend all day on a little boat taking depth readings and making your own chart, but if you’re anything like [Clay] you could build a solar-powered autonomous robot to do it for you. He’s been working on the boat, which he calls Gumption Trap, for the better part of a year now. If we had to guess, we’d say the experience of designing and building it has ended up being a bit more interesting to him than the actual depth of the water — but that’s fine by us.

The design of the boat is surprisingly economical, as far as marine designs go. Two capped four-inch PVC pipes are used as pontoons, and 3D printed brackets attach those to an aluminum extrusion frame that holds the electronics and solar panel high above the water. This arrangement provides an exceptionally stable platform that would be all but impossible to flip under normal circumstances.

Around the back of the craft, there’s a pair of massive 3D printed thrusters, complete with some remarkably chunky printed propellers. The lack of rudders keeps things simple, with differential thrust between the two motors enough to keep the Gumption pointed in the right direction.

Continue reading “Mapping The Depths With An Autonomous Solar Boat”

Cosmic Ray Navigation

GPS is a handy modern gadget — until you go inside, underground, or underwater. Japanese researchers want to build a GPS-like system with a twist. It uses cosmic ray muons, which can easily penetrate buildings to create high-precision navigation systems. You can read about it in their recent paper. The technology goes by MUWNS or wireless muometric navigation system — quite a mouthful.

With GPS, satellites with well-known positions beam a signal that allows location determination. However, those signals are relatively weak radio waves. In this new technique, the reference points are also placed in well-understood positions, but instead of sending a signal, they detect cosmic rays and relay information about what it detects to receivers.

The receivers also pick up cosmic rays, and by determining the differences in detection, very precise navigation is possible. Like GPS, you need a well-synchronized clock and a way for the reference receivers to communicate with the receiver.

Muons penetrate deeper than other particles because of their greater mass. Cosmic rays form secondary muons in the atmosphere. About 10,000 muons reach every square meter of our planet at any minute. In reality, the cosmic ray impacts atoms in the atmosphere and creates pions which decay rapidly into muons. The muon lifetime is short, but time dilation means that a short life traveling at 99% of the speed of light seems much longer on Earth and this allows them to reach deep underground before they expire.

Detecting muons might not be as hard as you think. Even a Raspberry Pi can do it.

A ginger cat, wearing a blue harness with a brass and wooden box on its back

Handmade GPS Tracker Keeps An Eye On Adventurous Cats

One of the most convenient things about having cats is their independent lifestyle: most are happy to enjoy themselves outside all day, only coming back home when it’s time for dinner and a nap. What your cat gets up to during the day remains a mystery, unless you fit it with a GPS collar. When [Sahas Chitlange] went searching for a GPS tracker for his beloved Pumpkin, he found that none were exactly to his liking: too slow, too big, or simply unreliable. This led him to design and build his own, called Find My Cat.

Continue reading “Handmade GPS Tracker Keeps An Eye On Adventurous Cats”

Giving Your Pets A Digital Squeak

A pet tracker has a particularly grueling set of requirements: small, light, rugged, incredibly long battery life, safe for the pet, and cheap. [Mihai Cuciuc] was looking at the options and wasn’t thrilled with any of them. So as any hacker would, he rolled his own, dubbed Squeak.

It uses an RN2483 module as it is a LoRAWAN module with publically available firmware from Microchip itself. This means [Mihai] could add his code and keep the modem code without having to reverse engineer everything or add a second microcontroller. In addition to the modem, there’s a GPS unit connected via UART. The clever part is the dual voltage regulators — the one powering the GPS is enabled or disabled by the RN2483. In addition, the RAM V_BACKUP line is always powered, which means the RN2483 can power up the GPS and let it get a quick fix (thanks to the RAM backup line).

To maximize the chances of a packet making it through, he made them only have the bare essentials. There are return packets to change the tracker’s mode (such as uplink interval or how often to capture GPS). With some cloud support, [Mihai] created infrastructure to capture the packets and relay them to Telegram. He can request the last location, receive updates, and change modes.

We’ve got you covered if you’re interested in tracking some of your dog’s other habits.