The Katzentracker Is a Tiny, SAM R34-Powered LoRa Locator, Crammed Into the Size of a Coin!

I've often wondered about the secret life of my cats.

Well, not so much my current ones — they have a heady lifestyle of eating and sleeping, occasionally venturing outside to dream of catching a squirrel.

Previous feline family members have spent days away from home, and who knows what they got up to. A second family? Having a go at the feral lifestyle? Your guess is as good as mine!

I'll never know where they wandered to, but I might be able to figure it out with future fuzzballs thanks to Gerhard Peter (@katzentracker) and the incredible miniaturization of technology that allows for such designs as the Katzentracker GPS LoRa tracking board, which we're going to look at today!

Katzentracker?

German for cat tracker, this project aims to put an end to the mystery of where the moggy has gotten to, by squeezing GPS along with an accelerometer, MCU and LoRa long-range radio into a tiny 30mm coin, purr-fect for attaching to your pet's collar!

This is no small feat. The factual matter is that there is not really even enough room to properly design a LoRa antenna layout in a 30mm disc. And then there is the rest of the circuitry to cram in! Let's take a look at what's going on here!

Make mine a module, please...

The host MCU in this platform is the Microchip SAM R34 — a 32-bit Cortex-M0 similar to the SAM D21 MCU, but also packing a Sub-GHz radio transceiver. This allows it to transmit and receive on LoRa-modulation scheme wireless networks (LoRaWAN), such as TTN — perfect for a solution where you expect gateway coverage.

The above map might look somewhat sparse, but we need to remember that LoRa is "long range" — up to several km in urban environments is possible, and line of sight links up to 15km in open areas are typical!

And where as many of us would likely choose to design in a module, rather than a discrete SiP implementation, the Katzentrakcer also does just that, in electing to use a module provided by Embit — the EMB-LR1276S.

Having laid out a previous, similarly sized project — RF is not fun at that board scale, and anything that can take away from the nightmare of the antenna design alone is a blessing — so more modules please!

It's great to see the SAM R34 again — we've taken a look at it previously with the BastWan boards from Electronic Cats. These boards also use a modular solution for the R34, this time the RAK4260 from RAK Wireless.

Modules certainly do make things a bit easier to manage all round!

This team also kindly released an Arduino Core board support package for the R34 SiP, complete with working code and examples that demonstrate the use of the LoRa radio front end!

Everything is an antenna. The magic is in designing one that works...

Getting a LoRa tuned antenna into such a small space takes some doing, and some clever engineering from the antenna manufacturers. We are now seeing ceramic packaged parts that pack all of the magic and voodoo that makes a good antenna into ever smaller and smaller footprints.

With a Pulse Larsen part chosen that not only has a small footprint, but a space optimized and forgiving ground plane layout associated with it, designs such as this tracker are now possible, without going off spec!

For comparson, here is the layout required for a similar part from a different manufacturer. Note that this part even requires an external trace to complete the antenna, which should also have an associated ground plane, as shown below.

Parts like this don't fare well for small PCB layouts, so we have to give a nod to Peter for finding such a suitable part for this project!

A tiny tracker needs a gnat-sized GPS...

We all know how GPS works, but we might not all be so aware that you can now get a GPS module complete with patch antenna, which will happily sit on the end of your fingertip!

The Micro Hornet (ORG1410) from Origin GPS is truly tiny — they claim to be the world's smallest GPS module!

I was not even aware you could get GPS antennae down at this scale, so a module with integrated antenna that is 10mm² is truly impressive to me!

Step counting isn't just for humans, oh no!

With a minute, 2mm² footprint, the BMA400 tri-axial accelerometer from Bosch Sensortec lets you track your movement across three axes, while merely sipping on power, and slipping into the smallest slice of board area.

This MEMS part quotes 3.5μA current consumption ("average use case"), step counting functionality at 4μA and as low as 800nA in deep sleep mode! Not only small on space, but also light on the power budget!

Last time we saw this part pop up was in a similarly miniature sized, module-based ESP32-powered device, the Open SmartWatch project — from pauls_3d_things — which we covered last year.

Speaking both I2C and SPI, it's a nifty part to keep in mind for when board space is at a premium.

Moving foward...

While the Katzentracker project isn't open source, we've taken a look at the modular approach to the design, and hope that the observations might help guide others who might be interested in fabricating their own femto-sized feline trackers — or application derivatives thereof!

If you would like to take a closer look at the Wiki for this project, it can be found here!

Katzentracker is on Twitter, where future updates will likely be found.