snappergps-pressure-sensor-daughterboard

Author: Jonas Beuchert

Pressure sensor daughter-board for SnapperGPS receiver (v1.0.x or v2.0.x).

Table of contents

• Files
• Manufacturing
• Components
• Assembly
• Flashing
• Usage
• Acknowledgements

Files

Note: There are two releases of the daughter-board, v1.0 and v2.0. While v1.0 is tested, it has a bug that prevents it from being soldered directly onto a SnapperGPS receiver without use of additional wires. In contrast, v2.0 fixes this bug, but has not been tested yet.

• gerber: Gerber files and drill file for manufacturing the daughter-board.
• bom.csv: Bill of materials of the daughter-board components.
• pcb.json: PCB layout file of the daughter-board. Created with EasyEDA.
• pick-and-place.csv: Centroid / pick-and-place file for assembly.
• schematic.json: Schematic file of the daughter-board. Created with EasyEDA.
• schematic.pdf: Schematic as PDF.

Manufacturing

• Get some PCBs manufactured by a PCB manufacturer of your choice. (I used JLCPCB, Aisler, or PCBWay in the past.) For this, upload the gerber folder to the manufacturer's website. Choose a two-layered PCB with size 3.56 mm x 11.68 mm.

• If you want, you can also let the manufacturer assemble the board(s) for you.

Components

designator	quantity	description	footprint	manufacturer part	manufacturer	supplier	supplier part	price
C30	1	100 nF capacitor	0402	CL05B104KO5NNNC	SAMSUNG	LCSC	C1525	$0.001
U2	1	pressure sensor		MS583730BA01-50	TE Connectivity	LCSC	C2887941	$11.391
R32, R34	2	10 kΩ resistor	0402	0402WGF1002TCE	UNI-ROYAL	LCSC	C25744	$0.001

Note: Most other SMD capacitors and resistors with the same value and footprint will also work.

Note: Instead of a pressure sensor from the MS5837-30BA series pressure sensor, you can also use a pressure sensor from the MS5837-02BA series. The MS5837-30BA series measures pressures up to 30 bar (~300 m depth), while the MS5837-02BA series is limited to 2 bar (10 m). However, it may be more suitable for measurements in air or shallow water, but you would need to adjust the firmware yourself.

Assembly

• Solder the two resistors, the capacitor, and the pressure sensor on the daughterboard. Ensure that the marked corner of the pressure sensor is aligned with the mark on the PCB. I recommend solder paste and a hot plate (or hot air gun) for soldering.

• Solder the assembled daughter-board on a SnapperGPS receiver. Note that only version v1.0.x and v2.0.x are compatible, not v2.1.x or 2.2.x). The five pads on the back of the daughter-board should connect to the five pads on the SnapperGPS receiver. The daughter-baord shall be orientated such that the pressure sensor sits in the corner of the SnapperGPS receiver.

• Package the whole assembly in a water/weather-proof way, which still exposes the gel-filled cavity of the pressure sensor. For example, I used silicon potting for this, but you can also use a rigid housing with a 3.07 mm hole combined with an O-ring with inner diameter 1.8 mm and cross-section diameter 0.8 mm.

Flashing

• Go to https://snappergps.info/flash or https://snappergps.github.io/snappergps-app-lite/flash.
• Connect the SnapperGPS receiver to your computer via USB.
• Pair the SnapperGPS receiver.
• Select the SnapperGPS-PressureSensor firmware.
• Flash the firmware.

Usage

Find instructions in the firmware repository.

Power consumption

All tests using a SnapperGPS v1.0.0 board and 3.7 V supply voltage with GNSS antenna and pressure-sensor daughterboard.

Sleeping current (SnapperGPS + pressure sensor): 1.9 uA ± 0.1 uA (similar to SnapperGPS without pressure sensor).

Charge consumption pressure measurement (SnapperGPS + pressure sensor): 0.0239 uAh ± 0.0015 uAh (about 10% of a GNSS snapshot).

Charge consumption GNSS snapshot + pressure measurement (SnapperGPS + pressure sensor): 0.2069 ± 0.0013 uAh (same as without pressure sensor).

Exemplary power consumption calculations

1) Power consumption per day

• Settings: Pressure measurement every second, snapshot every 64 seconds
• GNSS snapshots per day: 1350
• Pressure measurements per day: 86400
• Charge consumption sleeping current per day: 0.046 mAh (2%)
• Charge consumption pressure measurements per day: 2.030 mAh (86%)
• Charge consumption GNSS snapshots per day: 0.280 mAh (11.9%)
• Total charge consumption per day: 2.357 mAh (100%)

2) Power consumption to fill memory

• Settings: 64 pressure measurements per 1 GNSS snapshot
• Charge consumption for 22,000 GNSS snapshot: 4.56 mAh (12%)
• Charge consumption for 64 * 22,000 = 1,408,000 pressure measurements: 33.09 mAh (88%)
• Additional sleeping current per day: 0.046 mAh/day

Picture

Acknowledgements

This SnapperGPS daughter-board was developed by Jonas Beuchert in the School of Computer Science and Informatics of Cardiff University.

This repository is licensed under a Creative Commons Attribution 3.0 International License.