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Mobile POS · Offline-FirstFlutter · Dart · SQLite · ESC/POS

A beast of an offline POS app. Zero network lag, instant barcode scanning, and direct hardware integration for wireless printing because cloud dependencies suck.

CartSnap App POS interface

Client
CartSnapRetail & POS platform
Year
2024Completed & Shipped
Role
Lead DeveloperMobile architecture
Stack
Flutter · DartSQLite · ESC/POS
Status
ShippedProduction ready

CartSnap App is an offline-first POS application designed to solve connection delays in retail environments. Traditional cloud POS systems suffer from network lag and downtime; this app works fully local.

I built the system using Flutter and Dart, compiling to native binaries with direct micro-printer integration over ESC/POS commands. Instant barcode scans fetch items from a local SQLite cache in under 5 milliseconds.

The result is a lightning-fast checkout flow that operates in warehouses and remote retail sites with zero internet connection.

The Vision

Offline POS
running at peak speed.

Retail stores lose money when transaction flows hang. This POS app caches entire inventory models locally, allowing workers to scan items, generate invoices, and print receipts with zero network calls.

Hardware-level commands interact directly with portable Bluetooth/Thermal printers.

The Product

Check out in
under three seconds.

By structuring local indexing, product lookup is immediate. The receipt printer commands are queued locally and executed via Bluetooth channels instantly.

The app runs on low-cost Android tablets, lowering the hardware entry-barrier for local store owners.

CARTSNAP system diagram overview
CARTSNAP full system architecture overview.
Telemetry

Interactive 3 POS checkout.

01Checkout Basket & CartDemonstrating the Checkout Basket & Cart functionality built into the core stack.Local SQLite cache
02Local database searchDemonstrating the Local database search functionality built into the core stack.Offline inventory
03Bluetooth Printer connectionDemonstrating the Bluetooth Printer connection functionality built into the core stack.ESC/POS direct protocol
Architecture

Under the
hood.

A local SQLite database provides 5ms query speeds, synced to a Flutter app logic layer that manages printer queues and inventory indexing.

UI Layer
  • Flutter
  • Dart

Responsive mobile UI tailored for tablet layouts with double column panels.

Database
  • SQLite
  • drift

Indexed local store backing that holds catalog data, sales reports, and receipt templates.

Hardware
  • ESC/POS
  • Bluetooth Serial

Low-level connection streams that send formatting and print commands directly to thermal printers.

5msLookuplocal product index
100%Offlineno internet required
BluetoothPrintingdirect print commands
Outcome

Speed and
reliability unlocked.

0msNetwork lagfully local processing
Colophon

Created by a lone wolf.

Engineering & Design
Zenith Soumya
Flutter developer · POS architect
About Z.S

Zenith Soumya is an IoT & AI Developer. He designs and builds next-gen web applications, Java/DSA optimized tools, and micro-controller IoT systems.

CartSnap POS is compiled and packaged as an Android APK, distributed locally to store owners.

Download APK ↗All workBack home