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snappergps-pcb-2-1

This is an alternative version of the original SnapperGPS receiver. Just like V1.0.0, V2.0.0, and V2.2.0, 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:

  • Measures 27.3 mm x 36.4 mm,

  • Operates for more than a year on two button batteries,

  • Weighs 9.5 g or 13.0 g (depending on the type of batteries),

  • Has enough memory to provide about 22,000 position fixes,

  • Captures fixes in user-defined time intervals or externally triggered,

  • Needs only 12 ms of signal reception for a fix,

  • Employs multiple satellite systems for high reliability (GPS, Galileo, and BeiDou),

  • Achieves a median real-world tracking accuracy of about 15 m (before smoothing),

  • Maintains a real-time clock to accurately timestamp the fixes,

  • Measures the temperature in addition, and

  • 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 V2.1.0.

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.

SnapperGPS PCB
Figure 1: Top view (left) and bottom views (centre, right) of assembled SnapperGPS receivers V2.1.0 with a passive ceramic patch antenna and holders for two LR44 or SR44 button cells (centre) or two LR41 or SR41 button cells (right). This version is similar to V2.0.0, but does not come with GPIOs or a connector for an external antenna.

Table of Contents

  1. Changes from previous versions

  2. Workflow

  3. Getting started

  4. Repository Structure

  5. Professional Manufacturing

  6. Hand Assembly

  7. Testing

  8. Hardware Overview

  9. Pinout

  10. Bill of Materials

  11. Additional Resources

Changes from previous versions

The main changes from V1.0.0 are:

  • The antenna is integrated into the PCB. No external active antenna is used anymore.

  • The receiver is powered by two LR44, SR44, LR41, or SR41 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.

  • The board is a bit larger with 27.3 mm x 36.4 mm, although, this now includes the antenna and battery footprints.

  • The memory is large enough to collect data for 22,000 fixes. Initially, V1.0.0 only supported a smaller memory for 11,000 fixes, although, it can now be upgraded to the larger memory version, too.

  • The board (including antenna and batteries) weighs at least around 9.5 g. Depending on the choice of antenna and battery, this can be heavier or lighter than V1.0.0.

  • 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.

The main changes from V2.0.0 are:

  • An optional external active antenna cannot be used anymore.

  • No general-purpose input/output (GPIO) pins are exposed. Therefore, no daughter-board can be connected.

  • The board is a bit smaller with 27.3 mm x 36.4 mm.

  • The board (including antenna and batteries) can weigh as little as 9.5 g. This is a bit lighter than V2.0.0.

  • The board does not have an option to use a thicker 4 mm antenna, just a thinner 2 mm antenna. This reduces signal quality in contrast to V2.0.0 with the 4 mm antenna.

To summarise, V2.1.0 is a little smaller and lighter than V2.0.0 and should probably be the preferred version for deployments where size and weight are crucial. However, for deployments with less restrictive weight/size constraints, V2.0.0 with the 4 mm antenna should probably be preferred to improve signal quality. In addition, V2.0.0 is required if a daughter-board shall be connected.

Workflow

  • 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.

Getting started

You already have a SnapperGPS receiver? See here how to get started. The instructions are for V1.0.0, but V2.1.0 works very similar.

You need to build a receiver first? Keep reading.

Repository Structure

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.

Professional Manufacturing

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.

Hand Assembly

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.

Testing

Some basic testing:

  • 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).

  • Go to the Configure page and click/tap on Pair receiver.

  • The connected SnapperGPS receiver should now be selectable in a pop-up window.

  • 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.

  • 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.

  • Select some configuration parameters in the app and click/tap on Configure.

  • Disconnect the SnapperGPS receiver.

  • Record a few snapshots outdoors.

  • Reconnect the SnapperGPS receiver.

  • 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.

  • 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:

  • Record some data outdoors at a location with known coordinates.

  • Upload it via the SnapperGPS app.

  • Calculate the horizontal error between the estimated locations and the ground truth.

  • We obtained median errors of 10-12 m, depending on the scenario.

Measuring the power consumption:

  • Configure a SnapperGPS receiver using the SnapperGPS app.

  • Power the SnapperGPS receiver from an external DC source with 3 V.

  • Place an ammeter in series with the source.

  • 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:

  • Record the maximum of 21824 snapshots.

  • Transfer them to a host computer using the Transfer data button on the Upload page of the SnapperGPS web app.

  • Ensure that all 21824 snapshots have been transferred and are provided as download.

Hardware Overview

Please have a look at our paper.

Pinout

We expose the VDD, GND, RESET, SWCLK, and SWDIO pins of the MCU on the the PCB. The last two 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 five pads are labelled on the silkscreen of the PCB.

┌───────────────────────────────┐
│   ○     ○     ○     ○     ○   │
│  GND  RESET SWCLK SWDIO  VDD  │
│                               │

Bill of Materials

The table below lists the electronic components that are needed to assemble a single SnapperGPS board. For one component, you have got two options each to create different SnapperGPS versions based on an identical PCB:

  • J4, J5: These are the battery holders. Use the Keystone Electronics 2996 or 2996TR for LR44 and SR44 button batteries (Figure 1, centre), which are easy to source. Use Hong Kong CCD 704833 or similar for LR41 and SR41 button batteries (Figure 1, right). These are a bit harder to source, but using them saves about 3.5 g in total.
Designator Qty Manufacturer Part # Description/Value Package/Footprint Mounting Type Notes Supplier URL
C4, C8, C10, C12, C13, C14, C16, C17, C20, C23 10 Murata GRM155R60J104KA01D Ceramic capacitor, 100 nF 0402 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM155R60J104KA01D/490-6287-1-ND/3845484
C3, C5, C6, C7, C9 5 Murata GRM155R60J103KA01D Ceramic capacitor, 10 nF 0402 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM155R60J103KA01D/490-6286-1-ND/3845483
C21, C22 2 Murata GRM1555C1H180JA01D Ceramic capacitor, 18 pF 0402 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM1555C1H180JA01D/2854383
C11, C19 2 Murata GRM188R60J105KA01D Multi-layer ceramic capacitor, 1 uF, 6.3 V, X5R 0603 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM188R60J105KA01D/490-1550-1-ND/587755
C18 1 Murata GRM185R60J475ME15D Multi-layer ceramic capacitor, 4.7 uF, 6.3 V, X5R 0603 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM185R60J475ME15D/490-3892-1-ND/965934
C15, C26 2 Murata GRM188R60J106KE47D Multi-layer ceramic capacitor, 10 uF, 6.3 V, X5R 0603 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM188R60J106KE47D/490-12538-1-ND/5797528
C27 1 Murata GRM188R60G226MEA0D Multi-layer ceramic capacitor, 22 uF, 6.3 V, X5R 0603 SMD https://www.digikey.com/en/products/detail/murata-electronics/GRM188R60G226MEA0D/2334877
L2 1 Murata BLM15HB221SH1D Ferrite bead 0402 SMD https://www.digikey.com/en/products/detail/murata-electronics/BLM15HB221SH1D/6798444
R11, R12 2 Yageo RC0402FR-0715RL Resistor, 15R 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-0715RL/311-15LRCT-ND/2827914
R15, R16 2 Yageo RC0402FR-071KL Resistor, 1K 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-071KL/726513
R10, R13, R17 3 Yageo RC0402FR-074K7L Resistor, 4K7 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-074K7L/311-4-7KLRCT-ND/2827881
R7, R8 2 Yageo RC0402FR-075K1L Resistor, 5K1 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-075K1L/726624
R18 1 Yageo RC0402FR-076K8L Resistor, 6K8 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-076K8L/311-6-80KLRCT-ND/729589
R14, R19 2 Yageo RC0402FR-0710KL Resistor, 10K 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-0710KL/726523
R1, R2, R3, R4, R5, R6, R9 7 Yageo RC0402FR-07100KL Resistor, 100K 0402 SMD https://www.digikey.com/en/products/detail/yageo/RC0402FR-07100KL/311-100KLRCT-ND/729473
Q2 1 Jauch Quartz Q 0,032768-JTX310-12,5-10-T1-HMR-50K-LF Crystal, 32.768 kHz ±10 ppm, 12.5 pF, 50 kOhm 2-SMD SMD Possible substitute: Epsom, X1A0001410004 FC-135R 32.768KHZ 9PF https://www.digikey.com/en/products/detail/jauch-quartz/Q-0-032768-JTX310-12-5-10-T1-HMR-50K-LF/8108077
D1 1 Rohm Semiconductor SML-D12M1WT86 LED, yellow-green, 572 nm, 2.2 V 0603 SMD https://www.digikey.com/en/products/detail/rohm-semiconductor/SML-D12M1WT86/SML-D12M1WT86CT-ND/5843861
D2 1 Rohm Semiconductor SML-D12U1WT86 LED, red, 620 nm, 2.2 V 0603 SMD https://www.digikey.com/en/products/detail/rohm-semiconductor/SML-D12U1WT86/SML-D12U1WT86CT-ND/5843858
TCXO1 1 Connor Winfield D32G-016.368M Temperature compensated oscillator, 16.384 MHz 3.2x2.5 SMD Possible substitutes: EPSON, X1G005441030112 or TXC Corporation, 7Q-16.368MBG-T https://www.digikey.com/en/products/detail/connor-winfield/D32G-016-368M/3641696
U2 1 Skyworks Solutions Inc. SE4150L-R RF receiver 24-QFN SMD https://octopart.com/se4150l-r-skyworks+solutions-20439429
SAW1 1 Abracon LLC AFS20A42-1575.42-T3 SAW filter, 1.575 GHz, BW 42 MHz 4-SMD SMD https://www.digikey.com/en/products/detail/abracon-llc/AFS20A42-1575-42-T3/535-12069-1-ND/4075659
U1 1 Silicon Labs EFM32HG310F64G-C-QFN32R Microcontroller 32-QFN SMD Possible substitutes: EFM32HG310F64G-A-QFN32R or EFM32HG310F64G-B-QFN32R https://www.digikey.com/en/products/detail/silicon-labs/EFM32HG310F64G-C-QFN32R/336-6165-1-ND/10314104
U3 1 Nexperia PRTR5V0U2AX,235 TVS diode, 5.5 V SOT143B SMD https://www.digikey.com/en/products/detail/nexperia-usa-inc/PRTR5V0U2AX235/1727-5862-1-ND/2698064
IC1 1 Winbond Electronics W25N01GVZEIG NAND flash, 1 GBit WSON-8 SMD Possible substitute: W25N512GVEIG (512 MBit) https://www.digikey.com/en/products/detail/winbond-electronics/W25N01GVZEIG-TR/5803931
Q1, Q3, Q4 3 Rohm Semiconductor TT8M1TR Mosfet array N and P-channel, 20 V, 2.5 A, 1 W 8-SMD SMD https://www.digikey.com/en/products/detail/rohm-semiconductor/TT8M1TR/5042837
J1 1 JAE Electronics DX07S016JA1R1500 USB-C receptacle connector, 24 Pins (16+8 dummy), right angle through-hole https://www.digikey.com/en/products/detail/jae-electronics/DX07S016JA1R1500/11585731
ANT1 1 Taoglas GP.1575.25.2.A.02 GPS/GALILEO patch antenna 25x25 through-hole https://www.digikey.com/en/products/detail/taoglas-limited/GP-1575-25-2-A-02/2332643
U6 1 Texas Instruments TPS61291DRVT Boost Switching Regulator IC 6-WSON SMD https://www.digikey.com/en/products/detail/texas-instruments/TPS61291DRVT/5012070
U7 1 Taiyo Yuden MDMK2020T3R3MM Fixed inductor, 3.3 uH, 1.15 A, 178 MOhm 2x2 SMD https://www.digikey.com/en/products/detail/taiyo-yuden/MDMK2020T3R3MM/3479456
J4, J5 2 Keystone Electronics or Hong Kong CCD 2996 or 704833 Battery holder (LR44/SR44 or LR41/SR41) SMD Possible substitute: Keystone Electronics, 2996TR https://www.digikey.com/en/products/detail/keystone-electronics/2996TR/2746493 or https://www.aliexpress.com/item/32742124807.html

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.

Additional resources

Acknowledgements

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.

CC BY 4.0