GPS For A Graphing Calculator

GPS [Chris], graphing calculator hacker extrordinaire, has seen a few of his projects show up on the front page of Hackaday, mostly involving builds that turn graphing calculators like the TI-84 Plus shown above into something that copies a few features from a smartphone. His latest build, a hardware GPS module attached to the TI-84 Plus, is yet another feather in his cap of awesome and impractical addition to a classic piece of hardware.

There were two major technical challenges behind adding GPS to a graphing calculator. The first of these was powering a GPS sensor. Many a calculator modder has put a lot of work into documenting the USB port on the 84 Plus, revealing it is a USB OTG port, capable of serving as a host or device. It also supplies 5V of power to just about anything, burning through batteries as a result.

The next challenge was reading the data coming off the GPS sensor at 4800bps.The TI-84 Plus series of calculators have a series of interrupts that can fire at fractions of the 15MHz clock. By setting the timer up to fire every 197 clock ticks and dividing again by 16, [Chris] can read data at 4758.9bps. It’s close enough to get most of the data, and the checksum included in the NMEA protocol allows the software to discard bad messages.

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GPS Engagement Ring Box


[James] got engaged recently, in part thanks to his clever GPS Engagement Ring Box, and he sent us a brief overview of how he brought this project to life. The exterior of the box is rather simple: one button and an LCD. Upon pressing the button, the LCD would indicate how far it needed to be taken to reach a pre-selected destination. After carrying it to the correct location, the box would open, revealing the ring (and a bit of electronics).

Inside is a GPS antenna and a Stellaris Launchpad, which are powered by three Energizer lithium batteries to ensure the box didn’t run out of juice during the walk. To keep the lid closed, [James] 3D printed a small latch and glued it to the top of the box, which is held in place by a micro servo. Once the box reaches its destination, the microcontroller tells the servo to swing out of the way, and the box can then open. As a failsafe, [James] added a reed switch to trigger an interrupt to open the box regardless of location. It seems this was a wise choice, because the GPS was a bit off and the box didn’t think it was in the correct place.

Swing by his blog for more information on the box’s construction and the wiring. We wish [James] the best and look forward seeing his future hacks; perhaps he’ll come up with some clever ones for the wedding like our friend Bill Porter.

$20 GPS/GLONASS/Beidou Receiver

Sticking a GPS module in a project has been a common occurrence for a while now, whether it be for a reverse geocache or for a drone telemetry system. These GPS modules are expensive, though, and they only listen in on GPS satellites – not the Russian GLONASS satellites or the Chinese Beidou satellites. NavSpark has the capability to listen to all these positioning systems, all while being an Arduino-compatible board that costs about $20.

Inside the NavSpark is a 32-bit microcontroller core (no, not ARM. LEON) with 1 MB of Flash 212kB of RAM, and a whole lot of horsepower. Tacked onto this core is a GPS unit that’s capable of listening in on GPS, GPS and GLONASS, or GPS and Beidou signals.

On paper, it’s an extremely impressive board for any application that needs any sort of global positioning and a powerful microcontroller. There’s also the option of using two of these boards and active antennas to capture carrier phase information, bringing the accuracy of this setup down to a few centimeters. Very cool, indeed.

Thanks [Steve] for sending this in.

Heathkit Clock Updated with a PIC32 and GPS


One of [Bob’s] most treasured possessions is a Heathkit alarm clock he put together as a kid. Over the years he’s noticed a few problems with his clock. There isn’t a battery backup, so it resets when the power goes out. Setting the time and alarm is also a forward only affair – so stepping the clock back an hour for daylight savings time means holding down the buttons while the clock scrolls through 23 hours. [Bob] decided to modify his clock with a few modern parts. While the easiest method may have been to gut the clock, that wouldn’t preserve all those classic Heathkit parts. What [Bob] did in essence is to add a PIC32 co-processor to the system.

Like many clocks in the 70’s and 80’s, the Heathkit alarm clock was based upon the National Semiconductor MM5316 Digital Alarm Clock chip. The MM5316 operates at 8 – 22 volts, so it couldn’t directly interface with the 3.3V (5V tolerant)  PIC32 I/O pins. On PIC’s the input side, [Bob] used a couple of analog multiplexer chips. The PIC can scan the individual elements of the clock’s display. On the PIC’s output side, he used a couple of analog switches to control the ‘Fast’, ‘Slow’, and ‘Display Alarm/Time’ buttons.

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Fail of the Week: GPS module design

GPS is really fun to play with in your projects. But when [Trax] decided to build a GPS chip into his design the fun ended abruptly. Above you can see the section of the board devoted to the hardware. Unfortunately this PCB fails to provide any GPS location data whatsoever.

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Centimeter-level precision GPS for $900

[Colin] and [Fergus] have been working with GPS for years now, and like most builders of really cool things, they’re often limited by the precision of off-the-shelf GPS units. While a GPS receiver is usually good for meters of accuracy,  this just isn’t good enough for a lot of projects. What you need is centimeter-level accuracy, something the guys have managed to do with their Piksi GPS receiver.

Where most GPS receivers only look at the data coming from the GPS satellites orbiting overhead, the Piksi uses another technique, real-time kinematics (RTK), to determine the receiver’s location with exacting precision. The basic idea behind RTK is to look at the carrier frequency of the GPS signals at 1575.42 MHz. This frequency has a wavelength of 19 cm, compared to the alternating 1s and 0s of the that are transmitted at around 1 MHz, or about 300 meters between each bit. While centimeter-level precision isn’t possible with only one receiver, two of these Piksi boards – one base station and one on a vehicle, connected via radio link – can make for a very exacting high-accuracy GPS receiver.

Previously, commercial RTK GPS systems have cost thousands of dollars – making a quadcopter or other homebrew project that relies on this level of precision nonsensical. [Colin] and [Fergus] have built hardware that can bring the price of this setup to under $1000. As a bonus, the Piksi board can also receive from other constellations such as Galileo and GLONASS. A very impressive piece of hardware, and we can’t wait to see the applications.

Homebrew GPS gets ±1 meter resolution with a Raspberry Pi


We’ve been following the work of [Andrew Holme] and his homebrew GPS receiver for a while now. A few years ago, [Andrew] built a four-channel GPS receiver from scratch, but apparently that wasn’t enough for him. He expanded his build last year to track up to eight satellites, and this month added a Raspberry Pi for a 12-channel, battery-powered homebrew GPS receiver that has an accuracy of about 3 feet.

The Raspi is attached to an FPGA board that handles the local oscillator, real-time events, and tracks satellites automatically. The Pi handles the difficult but not time-critical math through an SPI interface. Because the Pi is attached to the FPGA through an SPI interface, it can also load up the FPGA with even more custom code, potentially turning this 12-channel receiver into a 16- or 18-channel one.

An LCD display attached to the FPGA board shows the current latitude, longitude, and other miscellaneous data like the number of satellites received. With a large Li-ion battery, the entire system can be powered for about 5 hours; an impressively portable GPS system that rivals the best commercial options out there.