This is an alternative version of the original SnapperGPS receiver V1.0.0. Just like V1.0.0, it is a small, low-cost, and low-power GNSS receiver intended for non-real-time wildlife tracking. It employs the snapshot GNSS technology, which offloads the computational expensive data processing to the cloud, and:
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Measures 36.4 mm x 31.2 mm,
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Operates for more than a year on two LR44 or SR44 batteries,
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Weighs 12.7 g or 17.7 g (depending on the version, both including LR44/SR44 batteries and antenna) or 3 g less with smaller LR41/SR41 batteries,
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Has enough memory to provide about 11,000 or 22,000 position fixes (depending on the version),
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Captures fixes in user-defined time intervals or externally triggered,
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Needs only 12 ms of signal reception for a fix,
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Employs multiple satellite systems for high reliability (GPS, Galileo, and BeiDou),
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Achieves a median real-world tracking accuracy of about 12 m (before smoothing),
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Maintains a real-time clock to accurately timestamp the fixes,
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Measures the temperature in addition, and
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Is configured via USB in your browser without the need to install a driver or an app.
This repository contains the hardware design files that can be used to replicate a SnapperGPS receiver V2.0.0.
If you use SnapperGPS hardware or software for research, please consider citing our publications.
For the hardware:
Jonas Beuchert, Amanda Matthes, and Alex Rogers. 2023. SnapperGPS: Open Hardware for Energy-Efficient, Low-Cost Wildlife Location Tracking with Snapshot GNSS. Journal of Open Hardware, 7(1): 2, pp. 1–13. https://doi.org/10.5334/joh.48.
For the cloud-processing software:
Jonas Beuchert and Alex Rogers. 2021. SnapperGPS: Algorithms for Energy-Efficient Low-Cost Location Estimation Using GNSS Signal Snapshots. In SenSys ’21: ACM Conference on Embedded Networked Sensor Systems, November, 2021, Coimbra, Portugal. ACM, New York, NY, USA, 13 pages. https://doi.org/10.1145/3485730.3485931.
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| Figure 1: Bottom and top view of a SnapperGPS receiver V2.0.0. |
Table of Contents
The main changes from V1.0.0 are:
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The antenna is integrated into the PCB. No external active antenna is required anymore. However, an external active antenna can still be used optionally.
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The receiver is powered by two LR44 or SR44 batteries rather than a lithium-ion polymer (LiPo) battery. These are easier to obtain, cheaper, and simpler to ship, but also a bit heavier and prevent the use of custom battery sizes. Alternatively, smaller and lighter LR41 or SR41 batteries can be used, which are harder to find than LR44 batteries, but still easier to ship than LiPo batteries.
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The board is a bit larger with 36.4 mm x 31.2 mm, although, this now includes the antenna and battery footprints.
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There are two version with different memory sizes, either large enough to collect data for 11,000 or 22,000 fixes. Initially, V1.0.0 only supported the smaller memory version, although, it can now be upgraded to the larger memory version, too.
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The board (including antenna and batteries) weighs at least around 10 g. Depending on the choice of antenna and battery, this can be heavier or lighter than V1.0.0.
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The energy consumption is a little lower with 1 μA sleeping current @ 3 V rather than 1-2 μA sleeping current @ 3.7 V. However, you should not feel the difference in practice.
You can also find a summary of the changes in this video.
To summarise, V2.0.0 should be easier to use and probably the preferred version for most applications rather than V1.0.0. However, if you really want to minimize size and weight, you might still want to look at V1.0.0 since it offers more options for customization.
- Get/build your SnapperGPS receiver (see sections below).
- Configure your SnapperGPS receiver in your browser for your deployment.
- Deploy your SnapperGPS receiver.
- The SnapperGPS receiver captures GNSS snapshots according to your configuration.
- Recover your SnapperGPS receiver.
- Upload the data from your SnapperGPS receiver to our server.
- Download the track of your surveilled animal.
You already have a SnapperGPS receiver? See here how to get started. The instructions are for V1.0.0, but V2.0.0 works very similar. For differences, check out this video.
You need to build a receiver first? Keep reading.
The two files .brd and .sch are CAD files that contain the PCB's board design and schematic, respectively. They have been created with Autodesk EAGLE 9.6.2, but should be compatible with other electronic design software.
The directory CAMOutputs includes the Gerber files and drill file, which are necessary for PCB manufacturing.
The two files .mnb and .mnt can be used for a pick-and-place machine and describe the component positions and orientations on the bottom and top layer, respectively.
The simplest way to replicate SnapperGPS is to upload the BOM, the Gerber files, the drill file, and the pick and place files to an online PCB manufacturing and assembly service. They will source the components, print the PCB, and assemble the board.
We recommend a thickness between 0.8 and 1.6 mm for the four-layered board. The thinner, the lighter. The substrate can be FR-4 and hot air solder leveling (HASL) or electroless nickel immersion gold (ENIG) can be used for the finish.
You can find an FAQ on prefessional manufacturing in the discussions forum.
An alternative to prefessional manufacturing is to just obtain the SnapperGPS PCB from a PCB manufacturer and to manually assembly the board. Hand-soldering a board takes less than 2 h for a skilled person, but requires intermediate equipment and skills and potentially additional time for testing, debugging, and re-work.
You can find instructions here.
Some basic testing:
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Open the SnapperGPS web app in Microsoft Edge or Google Chrome or download it from the Microsoft Store or Google Play. (Alternatively, you can also host the SnapperGPS web app yourself, as described in the snappergps-app repository).
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Go to the Configure page and click/tap on Pair receiver.
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The connected SnapperGPS receiver should now be selectable in a pop-up window.
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After pairing, confirm that the receiver information in the table on the top of the page is appropriate, including on-board time and firmware version. The snapshot count should be zero.
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Check the measured battery voltage in the table at the top of the Configure page. We recommend around 3 V before a long-term deployment.
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Select some configuration parameters in the app and click/tap on Configure.
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Disconnect the SnapperGPS receiver.
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Record a few snapshots outdoors.
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Reconnect the SnapperGPS receiver.
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Go to the Upload page and follow the instructions to upload the snapshots from the SnapperGPS receiver to the server. Please select only snapshots for processing that you collected outdoors.
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Once processing is complete, inspect the calculated track on the Download page. There are also links to some of our tracks for comparison.
Testing the localisation accuracy:
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Record some data outdoors at a location with known coordinates.
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Upload it via the SnapperGPS app.
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Calculate the horizontal error between the estimated locations and the ground truth.
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We obtained median errors of 10-12 m, depending on the scenario.
Measuring the power consumption:
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Configure a SnapperGPS receiver using the SnapperGPS app.
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Power the SnapperGPS receiver from an external DC source with 2.7-3.3 V.
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Place an ammeter in series with the source.
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The current should be around 1 μA if the board is sleeping and the maximum current should be around 25 mA when capturing a snapshot. The charge consumption for a single snapshot should be <0.3 μAh.
Testing the flash memory:
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Record the maximum of 10901 or 21824 snapshots.
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Transfer them to a host computer using the Transfer data button on the Upload page of the SnapperGPS web app.
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Ensure that all 10901 or 21824 snapshots have been transferred and are provided as download.
Please have a look at our paper.
We expose the three general-purpose input/output pins (GPIOs) PA0, PA1, and PA2 of the MCU as well as the supply voltage pin VDD and the ground pin GND at an edge of the PCB. This allows to connect external modules to extend the functionality of the device. This can be done by soldering wires on the rectangular pads. For the functionality of the three pins, please refer to the pinout section in the datasheet of the EFM32HG310.
We also expose the VDD, GND, RESET, SWCLK, and SWDIO pins of the MCU on the back of the PCB. The last two ones allow for debugging or flashing using Serial Wire Debug (SWD). All five circular pads have a spacing of 0.1 in and, hence, the same as common PCB headers.
All ten pads are labelled on the silkscreen of the PCB.
Front │ │ Back
│ │
│ │ ○ GND
VDD □ │ │
│ │ ○ RESET
GPIO3/PA2 □ │ │
│ │ ○ SWCLK
GPIO2/PA1 □ │ │
│ │ ○ SWDIO
GPIO1/PA0 □ │ │
│ │ ○ VDD
GND □ │ │
────────────────┘ │
The table below lists the electronic components that are needed to assemble a single SnapperGPS board. For four components, you have got two options each to create different SnapperGPS versions based on an identical PCB:
- IC1: This is the memory chip. If you choose the Winbond Electronics W25N01GVZEIG with 1 GBit memory, then you can store up to 21824 snapshots while the Winbond Electronics W25N512GVEIG with 512 MBit provides enough memory for 10901 snapshots.
- J3: This antenna connector is optional and only needed if you would like to connect an external active antenna instead of using ANT1 or for debugging purposes (Figure 5).
- ANT1: This is the passive antenna on the board. The Taoglas GP.1575.25.2.A.02 (Figure 3, 4) is thinner (height: 2 mm) than the Taoglas GP.1575.25.4.A.02 (Figure 2, height: 4 mm), but both have the same footprint (25 mm x 25 mm). The weight difference is 5 g. If weight and size are crucial, choose the former, if not, choose the latter since it provides better signal quality.
- J4, J5: These are the battery holders. Use the Keystone Electronics 2996 or 2996TR for LR44 and SR44 button batteries (Figure 2, 3, 5), which are easy to source. Use Hong Kong CCD 704833 or similar for LR41 and SR41 button batteries (Figure 4). These are a bit harder to source, but using them saves about 3.5 g in total.
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| Figure 2: Bottom and top view of a SnapperGPS receiver V2.0.0 with holders for LR44/SR44 batteries and a 4 mm thick passive antenna. |
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| Figure 3: Top view of a SnapperGPS receiver V2.0.0 with holders for LR44/SR44 batteries and a 2 mm thick passive antenna. |
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| Figure 4: Bottom view of a SnapperGPS receiver V2.0.0 with holders for LR41/SR41 batteries and a 2 mm thick passive antenna. |
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| Figure 5: SnapperGPS receiver V2.0.0 with holders for LR44/SR44 batteries and an external active antenna connected via an U.FL connector. |
The BOM differs slightly from the one for initial SnapperGPS test boards, which was cheaper. For example, we used cheaper TCXOs, the X1G005441030112 manufactured by EPSON or the 7Q-16.368MBG-T from the TXC Corporation, which cost around $2 instead of the expensive D32G-016.368M that costs $7-$8. We had to introduce this change because of the on-going global supply chain disruptions and recommend to revert to one of the initial choices for replications, if possible, to reduce the overall cost.
This SnapperGPS receiver version was developed and is maintained by Jonas Beuchert under supervision of Alex Rogers in the Department of Computer Science of the University of Oxford.
Jonas Beuchert is funded by the EPSRC Centre for Doctoral Training in Autonomous Intelligent Machines and Systems (DFT00350-DF03.01) and develops SnapperGPS as part of his doctoral studies. The implementation of SnapperGPS was co-funded by EPSRC IAA Technology Funds (D4D00010-BL14 and D4D00190-BL03.01).
This documentation is licensed under a Creative Commons Attribution 4.0 International License.
SnapperGPS V2.0.0 is certified as open source hardware by the Open Source Hardware Association with UID UK000049.
