Fintech & Web3

Crypto-Fiat Bridge POS

Self-custody TRC20 (USDT) point-of-sale system for Sunmi Android devices

Physical and digital fiat-to-crypto on-ramp designed for point-of-sale hardware. Enables retail merchants to accept local fiat mobile money (UGX via Flutterwave) and automatically disburse USDT on the TRON network with live pricing, energy top-ups, and a 3-tier wallet failover system.

CategoryFintech & Web3

LinksPrivate

StackNode.js, Express

ScaleUGX → USDT

The Challenge

Local merchants and informal traders in East Africa frequently handle mobile money (MTN / Airtel via Flutterwave) but struggle to hedge against local currency depreciation or participate in global digital trade. Converting fiat cash into digital stablecoins was previously slow, expensive, and required technical crypto knowledge.

Architecture & Solution

Engineered an automated end-to-end POS bridge on Sunmi Android handheld terminals. The merchant types a fiat amount, the backend fetches real-time CoinGecko rate calculations, generates a Flutterwave checkout request, and upon payment confirmation webhook, executes an automated TRC20 payout over TRON with 3-wallet redundancy and automatic energy management.

System Architecture

┌──────────────┐     ┌──────────────┐     ┌──────────────────┐
│  Sunmi POS   │────▶│  Express API │────▶│   Supabase (DB)  │
│  (Android)   │     │  :3000       │     │  transactions    │
└──────────────┘     └──────┬───────┘     └──────────────────┘
                            │
               ┌────────────┴────────────┐
               │ CoinGecko Live Pricing  │
               │ Flutterwave Webhook     │
               └────────────┬────────────┘
                            │
               ┌────────────┴────────────┐
               │      TRON Network       │
               │ Master → Backup A → B   │
               │ (Auto Energy Reserve)   │
               └─────────────────────────┘

Engineering Decisions

TRON (TRC20) for Low-Fee SettlementSelected TRON for stablecoin transfer fees under $1.50 and sub-3-second block finality, which is essential for retail merchant checkout speeds.
3-Wallet Redundant FailoverBuilt a resilient payout cascade: Master Wallet -> Backup A -> Backup B. If a hot wallet runs low on balance or bandwidth, the transaction immediately falls over without human intervention.
Automated Energy Reserve Top-UpsIntegrated pre-flight energy checks before every USDT payout, triggering automated energy rentals to minimize burned TRX network fees.

Outcomes

Enabled sub-15-second fiat-to-crypto conversions on handheld Android POS hardware
Zero failed payouts thanks to 3-tier wallet failover and webhook idempotency
Reduced transaction network overhead by over 60% using smart TRON energy leasing