Wiring — OLED Display

v0.1: OLED Fake Data (no OBD needed)

0.96” SSD1306 OLED (LAFVIN kit) → ESP32

Board pin order: GND VCC SCL SDA (left to right)

Power source: Laptop USB → ESP32 USB port. Powers everything. No external power needed.

graph LR
    subgraph Power
        USB[Laptop USB]
    end

    subgraph ESP32
        E_USB[USB Port]
        E_3V3[3.3V]
        E_GND[GND]
        E_21[GPIO21]
        E_22[GPIO22]
    end

    subgraph SSD1306 OLED
        O_VCC[VCC]
        O_GND[GND]
        O_SCL[SCL]
        O_SDA[SDA]
    end

    USB -->|USB cable| E_USB
    E_3V3 -->|Red| O_VCC
    E_GND -->|Black| O_GND
    E_22 -->|Orange| O_SCL
    E_21 -->|Blue| O_SDA

WARNING: Always check labels on YOUR board before wiring — pin order varies by manufacturer.

v0.2: OLED + Real OBD Data (Bluetooth ELM327)

DO NOT BUY A USB-STYLE ELM327 CABLE. The ESP32 dev board’s USB port is for flashing and power only — it cannot act as a USB host. A USB-style ELM327 cable needs to plug into a host (like a laptop). A female-to-female USB adapter between the cable and the ESP32 does nothing electrically and will not work. You also do not need a CP2102 / USB-to-UART bridge.

Buy a Bluetooth ELM327 dongle instead. It plugs directly into the car’s OBD2 port and talks to the ESP32 wirelessly over Bluetooth Classic.

How it works

An ELM327 Bluetooth dongle plugs into the car’s OBD2 port and broadcasts a Bluetooth Classic SPP (Serial Port Profile) radio link. The ESP32 has built-in Bluetooth — it pairs with the dongle and opens a virtual serial stream. The ELMduino library treats that stream exactly like a hardware UART, so all OBD2 query code from v0.1 can be reused unchanged.

No soldering. No UART tap. No voltage divider. No CP2102. No opening any housings.

Shopping list

Named brands (Vgate iCar, OBDLink LX, KIWI 3) are reliable. €10–€30 generic dongles work but pairing can be finicky.

Wiring (OLED unchanged from v0.1)

Exactly the same as v0.1 — only the data source changes, not the hardware wiring:

Bluetooth link

graph LR
    subgraph BMW
        OBD[OBD2 Port\n12V + CAN]
    end

    subgraph BT ELM327 Dongle
        DONGLE[ELM327 + BT Radio]
    end

    subgraph ESP32
        BT[Built-in BT Classic Radio]
        E_USB[USB Port - power only]
        E_3V3[3.3V]
        E_GND[GND]
        E_21[GPIO21]
        E_22[GPIO22]
    end

    subgraph SSD1306 OLED
        O_VCC[VCC]
        O_GND[GND]
        O_SCL[SCL]
        O_SDA[SDA]
    end

    subgraph Power
        USB[Laptop USB or Car 5V]
    end

    OBD ---|plug in| DONGLE
    DONGLE -.Bluetooth Classic SPP.-> BT
    USB -->|USB cable| E_USB
    E_3V3 -->|Red| O_VCC
    E_GND -->|Black| O_GND
    E_22 -->|Orange| O_SCL
    E_21 -->|Blue| O_SDA

Pairing procedure

1. Plug the BT ELM327 dongle into the car’s OBD2 port
2. Turn ignition to accessory (key position 1) so the OBD bus is powered
3. From a phone, pair to the dongle once — note the Bluetooth name (usually OBDII, OBD2, or V-LINK). Most cheap dongles use “Just Works” pairing with no PIN.
4. Put that name into the ESP32 sketch as ELM_NAME
5. On boot, the ESP32 scans for that name, connects, and opens the serial stream

NOTE: Name-based pairing is the simplest path for cheap dongles. If your dongle has the same name as a common model (many call themselves OBDII), you can also connect by MAC address with SerialBT.connect(macAddr). Find the MAC on macOS / Linux via hcitool scan or bluetoothctl.

Code sketch — ELMduino over BluetoothSerial

This is the real v0.2_oled_real_obd.ino pattern — what the project actually uses:

#include <BluetoothSerial.h>
#include <ELMduino.h>

BluetoothSerial SerialBT;
#define ELM_NAME "OBDII"    // change to match your dongle's BT name
ELM327 myELM327;

void setup() {
  Serial.begin(115200);

  SerialBT.begin("BMW_DASH", true);          // master mode
  if (!SerialBT.connect(ELM_NAME)) {
    Serial.println("BT pair failed");
    return;
  }

  if (!myELM327.begin(SerialBT, false, 2000)) {
    Serial.println("ELM327 init failed");
    while (true);
  }
  Serial.println("ELM327 ready");
}

void loop() {
  float rpm = myELM327.rpm();
  if (myELM327.nb_rx_state == ELM_SUCCESS) {
    Serial.printf("RPM: %.0f\n", rpm);
  }
}

The full sketch with a non-blocking poll schedule (RPM polled more often than oil temp), auto-rotating OLED screens, and reconnect logic is on the v0.2 sketch page.

Power

• Dev: laptop USB → ESP32 USB port (same as v0.1)
• In-car (v1.1+): MP1584 buck converter from fuse box 12V → 5V → ESP32 VIN

NOTE: ESP32 Bluetooth Classic uses around 45 KB RAM. Plenty of headroom on the stock ESP32 DevKit, but if you ever port this to an ESP32-C3 or -S2, those don’t have Classic BT — only BLE — and most ELM327 dongles speak Classic.