I was on the lookout for a cheap, GPS cycling computer when I first saw XOSS G / G+. I used Strava with 
my smartphone for about 2 years. It was bulky, battery drain was too much because of GPS and huge screen, and not nice when you fall down, crash, or in any case of rainfall. Garmin or Polar units was nice, but needlessly expensive. Besides, no mapping functionality needed. XOSS came to life as a KickStarter project and mass production began in 2019, August.
I’m not sure if XOSS was the first introduce sub-50$ GPS enabled unit (XOSS G is on sale now, currently 25$), but they democratised the access to GPS enabled cycling computers. It’s not sold in here, I didn’t want to wait AliExpress which may take up to 2 months, so I bought one second hand.
Before talking about any specifications or technical data, I must say these units are very handy. They are also very easy to use: just long-press the right key, device boots instantly, then you wait for “cold boot” for about 30 seconds while your XOSS G unit scans for satellites. It’s a very small and light device, mine came with extra long attachment arm and nice silicone sleeve. I’ve seen people complaining about smartphone app, especially synching to Strava. They made a huge update, and now Strava sync is not just painless, it works fast, looks nice, and even have plenty of functionality that is enough for most
people if you want to use the device without Strava connection.
Before diving into specs, you may have already noticed, there are 2 versions: XOSS G and XOSS G+. Plus model is about 10$ more expensive now, but it can connect to Cadence, Speed, Heart Rate sensors. Both models have identical chassis, screen size, weight. In fact, the only real difference is the LCD (more on that later). Mind you, it cannot connect to Power Meters if you have any. This makes sense; no need to bother for creating software / hardware for Power Meters, which have sky-high prices. Probably, if you have Power Meter, you will need a more advanced devices, though.
On G+ model, lower part of the LCD is divided into 4 quadrants instead of 2, and these digits display cadence and heart rate. If you connect a speed sensor, device reads speed data from wheel sensor; otherwise, GPS is used for speed.
Standard package does not include much accessories; 2 rubber bands, device mount, and a shortish Micro USB for charging. Mount is Garmin compatible, so you can find many alternatives. Mine came with a Sram-made, long-arm mount, which is funnily about 20$ here, almost the same money as the device itself: in fact, with silicone sleeve which is another 19$, device itself comes free, so was a good deal ! (I paid 40$ for all; unit was barely used with only few kilometers clocked, came complete with original packaging intact) It does have automatic backlight, which goes on dark automatically and its pretty bright. Obviously, it does have a 7-segment LCD display instead of a graphical one. 500mAh lithium-ion battery keeps the device running for 25 hours; which is quite accurate. With backlight on, you’ll probably won’t get half of it.
I opened up the device, being a curious developer guy (for almost 30 years) and having an electronic hobby. Before I dive into that, I want to talk about specifications, and obviously pros and cons for me. I don’t do reviews.
- 9 possible data on the 3 tabs of its 1.8″ LCD screen.
- IPX7 water resistance.
- 4 built-in GPS systems: GPS/GLONASS/BeiDou/Galileo.
- Built-in barometer.
- Bluetooth v5.0, XOSS APP and STRAVA and TrainingPeaks compatible.
- 25 hours of battery life.
- 1.8-inch LCD screen
- Three backlight modes: automatic, normal and closed.
- Adaptive angle display
- Anti-glare
- Sensors and functions:
- GPS / GLONASS / GALILEO / BeiDou
- 9 types of data: speed, time, current distance, average speed, altitude, slope, maximum speed, clock, total mileage
- Barometer
- IPX7 resistance
- Dimensions: 4.8 x 7.4 x 1.91 cm
XOSS G and G+ have only 2 buttons. No touchscreen. You get a 1.8 inch, 7-segment display with large fonts, readable under any condition. Right button power on / off the device, and when powered on, used to navigate between 3 screens. Left button pauses recording. It can also auto-pause when you stop (denoted by a “A” sign near pause sign on top). Pushing left button long stops recording, and your ride data is stored. There is no way to access your old data on the device itself: you connect to device with your smartphone, and app synces data, create a map and vital metrics as in Strava, and shares the data to Strava or TrainingPeaks (not tested TrainingPeaks, though). The interface of XOSS App is expectedly resembles Strava.
XOSS G (not G+) displays 9 data on 3 screens. The top of the screen resembles a smartphone, with various icons like GPS signal strength, screen name, ride status (on, pause or auto-pause), battery level etc. SPD screen displays current speed with big fonts; under it, total time elapsed and odometer for current ride. These units don’t have “Lap” functionality, which is no use to me. AVG, second screen (Which is average for short), displays Average Speed, Altitude and Grade. Last screen, named “MAX”, displays the max speed you achieved, current time, and total km’s (or, miles according to your settings).
Long pressing both buttons together bring up the settings interface, which is not much. You can just set Time Zone and Metric/Imperial unit selection. But the app itself let you adjust a few settings more, like beeping on/off, backlight (like always off, automatic or always on). There is also firmware update option. Do not expect huge changes between firmware updates: this unit have a character LCD, and the SoC (chipset, whatever you want to call it) is pretty barebones.
It can connect to GPS, Galileo and and Glonass satellites
Connection time takes less then 30 seconds, and GPS is accurate, not plotting jagged edge lines like some smartwatches do. It’s probably not precise enough to launch ballistic missiles, but the Chinese-made UnicoreComm UFirebird UC6226 powers this devices’ GPS functionality with great success. It’s not fancy as highest end u-blox ZED-F9R, which can connect to 4 satellite systems simultaneously – but about 100 times cheaper!
Your data, like GPS coordinates, cadence / HR if you have, is written to a 64MB Flash in device.
I cannot comment on sensor compatibility (like HR, Cadence, Speed etc) as my particular model (G) does not support them.
What I like about it
It’s a cheap, lightweight and dependable device; which I know won’t let me down, unlike complex devices like Hammerhead Karoo, which runs on Android, and about 7.342 billion things can go wrong. Screen is large enough, readable, everything is well planned. It feels like an old Apple device, which gets the job done with a decent price, good interface, high useability, simplicity and sturdiness. (Not the new ones that costs gold, ripped off functionality, fragile).
It’s IPX7 certified, at least, claims so, meaning it is waterproof up to 30 minutes under 1m water. If you don’t do bike diving, you cannot destroy it. Get the silicone sleeve, and preferably devise a screen protector. I dropped it a few times, and it survived.
One thing I liked most is the simplistic nature of its innards: it’s not ultrasonic welded, you can open it up with standard Phillips screwdrivers. I have great concern about batteries, because many devices
becomes junk once their proprietary design battery dies out. This unit has a standard off-the-shelf, 3.7v, 503035 type, lithium ion polymer battery. To replace it, you just need a Philips screwdriver of correct size and a soldering iron.
These batteries typically costs ~10-15 dollars for really good ones, but you can get them at probably 2-3$, but won’t last long. Looks like the shell will permit a larger battery, too. Yet, you can get away with these kinds of batteries for most Garmin devices, I guess. (Looks like Garmin batteries do not have charge control circuit built into battery, so you may get “ic-less” cells for even cheaper – also first Hammerhead Karoo uses these types of batteries, which is 653565, which is strange because LP653566 is a standard size, but seems like 653565 is not. Anyway, it will fit though).
If you can, get XOSS G+ instead. I’ll have to change my trusty XOSS G some time, because now I need HR and Cadence data.
Smartphone app is surprisingly good, looks pro and nicely designed unlike many similar apps, and got hugely better since I got the device. Strava sync is great.
What I didn’t like about Xoss G
Nothing, except for 2 things: I started to get an annoying buzz from mount area; and noticeable slack, but not sure if its the Sram, or the unit itself. This minor problem can be solved by adding a thin plastic or even cardboard liner to the base. Other thing I don’t like is, I got the wrong unit because I was in a hurry. If I bought the XOSS G+, probably I’d never replace it.
The “calorie” issue
XOSS seemingly multiplying actual calories spent with 2.5x, or even 3x.
I downloaded a .fit file from the smartphone app, and opened it: well, the device itself counts the calories internally and sends to Strava directly. Previously, I was suspecting that device is sending some abnormal data, like a super high cadence like 500rpm(!) or, maybe 500kg of rider weight(!). No. This needs a firmware fix, if can be resolved at all.
This is not a huge bummer, but ridiculous to show out to the world that you have 3x faster metabolism then an ordinary human.
In-depth analysis (Only for geeks)
Some of my readers (hope there are!) may be pissed off, because why this..in a bike blog? Well, this is a blog, so I can get a bit personal. And after all, some people like tinkering with their bikes, including me. I’d like to encourage or help people build new things, that’s why I’m sharing my thoughts that anyone can lookup somewhere else. If you’re interested in Arduino, Raspberry Pi, or any other single board computer,
you can buy some components and build your own. 20 years ago, it was almost impossible to make a device like XOSS G/G+, because access to components were tough, no internet to get help, and IC’s are not at this level. If you want to build a radio communication board, you would plan and implement it yourself, which needs an engineering background, lots of components and lots of failure. Today, we can have all types of communications protocols on a single IC, much more smaller then a stamp.
Ok, I open up the device, and as I guessed, it’s very simplistic but overall, a very good, well-though implementation. I’m no expert in soldering, but saw many badly soldered units, and horrible PCB designs. PCB looks very decent, and soldering is nice; I won’t expect any cold-solder related problems. Generally, I ride in half gravel – half rough asphalt with this unit, and my bike has 700x32c half-slick tires, no suspension. So, expect a lot of vibration. I dropped the unit a few times, and nothing broke. So I’m very pleased with quality. Oh, unexpectedly, plastic quality is very good, too.
Ok, now let’s have a look at the guts of this XOSS G: I bet there is nothing different (except LCD) on the XOSS G+, because hardware for connecting the external sensors like Cadence or Heart Rate is already there (Xoss also makes sensors, and sells these units bundled as Garmin do).
When I spot the biggest IC, labeled “Vinka VK1621b”, I thought this should be a microcontroller that
communicates with peripherals and LCD, and I was wrong: This is a supersized, super smart LCD controller, not your pappa’s Hitachi HD44780. The symbols like GPS icons are stored in memory of it, and sent to LCD when needed. Generally, you create bitmap images, and store them in such controllers as HEX files, much like a JPEG file on your computer. It’s also responsible for generating tones for the buzzer, placed on the mount base. It seems to have a parallel interface only, thus programming it is similar to HD44780’s. This IC is produced by Shenzhen Vinka Electronic Technology Co, founded in 2000, which I never even heard of. They generally produce LCD controllers, Touch interface IC’s. Product line is quite narrow.
A smaller IC, UC6226NIS, is where magic happens. Another interesting manufacturer, Unicore, founded in
2009. They seem to be manufacturing GPS-related IC’s and boards only, but there are many high-end stuff in their portfolio. UC6226 seems their lower-end product, yet quite a capable one. Another bonus for XOSS is, they seem to be using the automotive grade version of this IC, which is much more resilient. Spec sheet says it can communicate with 4 systems, GPS, GLONASS, BDS, Galileo, while XOSS spec sheet doesn’t mention about BDS.
Another important IC to note is, Nordic Semiconductor N52832. This is a very popular IC, in a small add-on board form, for Arduino or Raspberry Pi users. This IC can be bought under 4$, and an immensely capable one: Supports Bluetooth Low Energy 5.2, NFC, ANT, and you can write your own proprietary, 2.4 Ghz protocol driver if you need to. It also supports huge range of protocols such as UART, SPI, TWI, PDM, I2S. Is that all? No! Does also have an ARM CPU onboard, (MCU, to be fair), 64 MHz Cortex-M4 with FPU. Might not mean much, but the MCU powering original Arduino, ATMEL328P was just 20Mhz, and 8 bit, with no FPU. It also has 512/256 KB Flash, 64/32 KB RAM depending on chip type, again, these numbers are enormous for a device like that.
I believe system works like this: N52832 is the “hub”; which reads GPS data from Unicore UC6226NIS via SPI interface, parses this data, and writes to both Vinka VK1621b (LCD Interface), but also to Flash (another IC on board), Winbond 25Q64JVS1Q, via SPI interface. This data is then read by smartphone app, again Nordic’s N52832 acting as a broker.
Such Flash IC’s are quite easy to access via SPI. This particular model is 64MB, and I suspect it can be upgraded to 256MB, or even more. Maybe I’ll try some time!
So basically, this is only 4 IC circuit, but passive components like resistors, capacitors, etc.
It would be so nice to tinker with this design, maybe using Raspberry Pi, or other ARM based SBC along Linux to add new features like map functionality.
I’m not an electronics expert in any way, but build circuits, tools time to time, as I worked with embedded systems in the past a lot. And I like electronics. Feel free to share your thoughts!
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