Redesigned/refactored/rewrote the core "Checkout flow" on our self-checkout kiosks, stabilized it to run smoothly for ~750,000 monthly transactions.

Integrated with a fingerprint reader and 3rd party backend for identity/age verification.

Integrated credit card processing via two flows: (1) direct-access to Ingenico card readers, and (2) via a 3rd-party docker service, that supports more card reader models but is not as responsive in terms of possible UX integrations. The two flows were of entirely different designs, so it was a lot of work to get both of them working side-by-side in the same codebase (major refactor/rewrite of payments layer), while still handling stored-value payments and age verification as before.

Integrated with a 3rd party price/discounts/tax system to override ours during checkout.

Occasional fixes on API and UI

Enhanced our in-house deployment system (Linux CLI in Python, web backend in Express, frontend in Vue.js) with support for sane version numbering, better logging for deployment failures.

Established Git code-review processes for development, and branching processes for supporting releases

Introduced CI/CD, lint, and unit tests

Upgraded from Python 2.7 to 3.5

Introduced Python type annotations

Investigated countless problems for our front-line support staff

rewrote event-reporting / data-collecting system, which was implemented redundantly, but inconsistently, in both VB.NET and C#. Backend was a Microsoft Azure Cloud-managed DB.

data sync for user accounts and training regimens prescribed by coaches.

misc work in Unity

misc work with 3d transforms/quaternions, to compute angles and velocities from raw sensor data.

Developed a "sensor library" for Android, encompassing GPS, Wifi, Bluetooth, Screen/Cable/Battery state, Music Playback, and Activity Detection (e.g walking vs driving); signals served as inputs for our context engine, to adapt the homescreen for the user throughout the day.

Greatly improved battery usage by optimizing GPS use (trading off responsiveness for battery versus quality of user experience); gathered battery stats from 100k+ real-world devices to test the effects of different battery-saving heuristics

Implemented a client-side context engine to reduce network calls by 90% ("thin-client" is great, but sometimes you need a "thick-client" :-p )

Organized and moderated a recurring "technical deep dive" session for our team, where we could present and teach each other about the architecture and design of various features, as well as new dev tools, frameworks, paradigms/processing.

Mentored junior engineers in how to develop, debug, troubleshoot within the Android framework with our choice of libraries (e.g. Dagger 2 dependency injection, RxJava for asynchronous work)

Introduced "Reactive Programming" and the RxJava library to the team and codebase, used it to solve a slow start-up time issue in our app.

Championed Behavior Driven Development through unit tests (Robolectric + Mockito for mocking/stubbing + our dependency injection framework)

Pulled the team together during a difficult company transition (Verizon acquisition) to build and deliver a new prototype app in 8 weeks, while engineering and product management were still in a chaotic state.

Technical lead for 6 months on a sub-team of 3 engineers, building a news feed backend for our homescreen; included client APIs and integration, and data plumbing for future news personalization efforts.

Implemented GPS location sensing using Google Play Services

Built diagnostic tools for analyzing and troubleshooting location accuracy.

Web API security using Keyczar library on Android and Python-Django backend.

Integrated Robolectric unit-testing and Robotium automation-testing frameworks, when both were in a very early stage (very little documentation, and it was poor/inconsistent/outdated at that!)

Performed production database migrations on tables with millions of rows.

General client and backend feature work