unsurv offline

An open source, privacy friendly, compact GNSS receiver with ESP32 and NFC for all your location based projects, including tracking surveillance cameras

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May 18, 2023

Project update 12 of 12

Battery Charger Components and Current Production Timeline

by Martin W

I want to give you an update on the current production timeline. After all, the campaign conclusion was at the start of 2022. So, let me try to explain why there is still no parcel at your door with a tiny NFC capable GNSS receiver.

(TL;DR is at the bottom)

After I was relatively sure that the campaign would end up being a success, I ordered all required parts of the project that were available at the time. In hindsight, this was a good decision since, for example, the ublox GNSS receiver price has increased by about 15% in the meantime. At that time, I still had implemented a power switching (USB / LiPo) circuit taken from a popular ESP32 dev board. The PCB review process showed that that circuit had a flaw that would a) cost some precious power and b) would not work 100% consistently.

Therefore, I decided to use a battery charger IC that included power path switching between USB and battery power. The BQ25181 had all the necessary features, great QFN form factor, protection features(input- and undervoltage protection, short protection, overcurrent protection) and a planned release of Q3 2022. However it is still marked as pre-production and TI seems to not be willing to be precise about its release date anymore (1) (2).

There is a feature equivalent tiny BGA IC, the BQ25180, where even my work creating a library to control the chip would not be in vain, since it is fully compatible. The new tiny form factor created some additional challenges, since I want to keep the design as accessible for repairs as possible. Although it’s not as easy as the QFN package, it is still possible to hand solder and potentially replaceable by hand if things go wrong in production. So after multiple delays, at this point I am now confident that within the next weeks we will start a pre-production run at a local assembly service, so expect some update about that soon.

In addition. I received a power profiler kit to better understand power consumption while active or in deep sleep. The next update will be about the results gathered with this new tool.

TL;DR: Faulty power switching circuit in old design, Texas Instruments delayed the replacement, new tiny form factor IC is difficult to solder but has same features, pre-production run will start within the next weeks, next update is about power analysis of unsurv-offline

See you soon.


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