TSI-Telemetry Architecture

System Overview

┌─────────────┐    BLE    ┌─────────────┐   WiFi    ┌─────────────┐
│   Car ECU   │◄────────►│    ESP32    │◄────────►│Phone Hotspot│
│  (OBD-II)   │          │  (firmware) │           └──────┬──────┘
└─────────────┘          └─────────────┘                  │
                                                      Internet
                                                          │
                                                  ┌───────▼───────┐
                                                  │  HiveMQ Cloud │
                                                  │ (MQTT Broker) │
                                                  └───────┬───────┘
                                                          │
                                                      Internet
                                                          │
                         ┌────────────────────────────────┴───┐
                         │         Mac Mini (Home)            │
                         │                                    │
                         │  ┌──────────────┐  ┌───────────┐  │
                         │  │ Python Bridge│─►│TimescaleDB│  │
                         │  │   (MQTT sub) │  │ (Docker)  │  │
                         │  └──────────────┘  └─────┬─────┘  │
                         │                          │        │
                         │                    ┌─────▼─────┐  │
                         │                    │  Grafana  │  │
                         │                    │(dashboard)│  │
                         │                    └───────────┘  │
                         └───────────────────────────────────┘

Why Cloud MQTT Broker?

The ESP32 connects to your phone's hotspot while driving. Your Mac Mini is at home behind NAT. They can't reach each other directly.

Solution: Use HiveMQ Cloud as an intermediary:

ESP32 publishes to cloud broker
Mac Mini bridge subscribes to cloud broker
No NAT/firewall issues
Free tier is sufficient

Data Flow

Car ECU exposes data via OBD-II port
ELM327 adapter translates OBD-II protocol to Bluetooth LE
ESP32 connects to ELM327, requests PIDs, parses responses
ESP32 connects to phone hotspot WiFi
ESP32 publishes telemetry to HiveMQ Cloud topic car/telemetry
Python Bridge (on Mac Mini) subscribes to HiveMQ Cloud
Bridge writes data to TimescaleDB
Grafana queries TimescaleDB, displays real-time dashboard

Why This Stack?

Why MQTT?

Lightweight protocol designed for IoT
Low bandwidth overhead
Pub/Sub model decouples producers and consumers
QoS levels for reliability
Works well over unreliable mobile connections

Why TimescaleDB over InfluxDB?

We switched from InfluxDB to TimescaleDB because:

Built on PostgreSQL (familiar SQL syntax)
Easier setup and querying
Better for complex analytics later
Hypertables handle time-series optimization automatically
Can mix relational and time-series data

Why HiveMQ Cloud over local Mosquitto?

ESP32 can't reach home network from mobile hotspot
No port forwarding or VPN setup needed
Free tier (10 GB/month) is plenty for telemetry
TLS encryption included
Reliable cloud infrastructure

Components

ESP32 Firmware Modules

Module	Responsibility
`BLEManager`	BLE connection to ELM327
`OBDParser`	Parse OBD-II responses
`CarData`	Data structure for telemetry
`DisplayManager`	Serial output formatting
`Config`	Configuration constants
`WiFiManager`	(TODO) WiFi connection
`MQTTManager`	(TODO) MQTT publishing to HiveMQ

Server Components

Component	Port	Purpose
TimescaleDB (Docker)	5433	Time-series database
Grafana	3000	Visualization
Python Bridge	-	MQTT to TimescaleDB
HiveMQ Cloud	8883	Cloud MQTT broker

OBD-II Protocol

Request Format

01 0C\r     <- Request PID 0C (RPM)

Response Format

41 0C 1A 2B  <- Response
│  │  │  │
│  │  └──┴── Data bytes (A=0x1A, B=0x2B)
│  └──────── PID (0C = RPM)
└─────────── Mode 41 = positive response to mode 01

PID Conversion Formulas

PID	Name	Formula	Unit
0x0C	RPM	(A*256 + B) / 4	rpm
0x0D	Speed	A	km/h
0x05	Coolant Temp	A - 40	°C
0x0F	Intake Temp	A - 40	°C
0x11	Throttle	A * 100 / 255	%
0x04	Engine Load	A * 100 / 255	%
0x0B	MAP	A	kPa
0x2F	Fuel Level	A * 100 / 255	%
0x0E	Timing Advance	A / 2 - 64	degrees
0x42	Battery Voltage	(A*256 + B) / 1000	V

Network Topology

┌─────────────────────────────────────────────────────────────────┐
│                         WHILE DRIVING                           │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│   Car                     Phone                    Cloud        │
│  ┌─────┐                ┌───────┐              ┌─────────┐     │
│  │ESP32│───WiFi────────►│Hotspot│───Cellular──►│ HiveMQ  │     │
│  └─────┘                └───────┘              │  Cloud  │     │
│                                                └────┬────┘     │
│                                                     │          │
├─────────────────────────────────────────────────────┼──────────┤
│                           HOME                      │          │
├─────────────────────────────────────────────────────┼──────────┤
│                                                     │          │
│                                                ┌────▼────┐     │
│                                                │ Bridge  │     │
│                                                └────┬────┘     │
│                                                     │          │
│                                                ┌────▼────┐     │
│                                                │Timescale│     │
│                                                └────┬────┘     │
│                                                     │          │
│                                                ┌────▼────┐     │
│                                                │ Grafana │     │
│                                                └─────────┘     │
└─────────────────────────────────────────────────────────────────┘