Scan an I²C sensor bus

Almost every Pi sensor speaks I²C: temperature/humidity, IMUs, small OLED displays, port expanders. This example is the Amalgame equivalent of i2cdetect -y 1 — it opens the bus, probes every address, and prints what answers. Then we read one register from a device to show the full round-trip.

Wiring

sensor VCC ── 3V3        sensor SDA ── GPIO2 (SDA1, pin 3)
sensor GND ── GND        sensor SCL ── GPIO3 (SCL1, pin 5)

I²C is a shared two-wire bus, so several devices can hang off the same SDA/SCL pins. Make sure I²C is enabled (see setup, step 3).

Code

namespace Demo

import Amalgame.Hardware

public class Program {
    // I²C addresses are read in hex; String_FromInt is decimal only, so
    // format a byte as two hex digits — pure Amalgame, no inline C.
    private static string Hex2(v: int) {
        let digits: string = "0123456789abcdef"
        let hi: int = (v / 16) % 16
        let lo: int = v % 16
        return String_CharAt1(digits, hi) + String_CharAt1(digits, lo)
    }

    public static void Main(string[] args) {
        let busNum: int = 1
        let bus: I2c = new I2c(busNum)        // /dev/i2c-1
        if (!bus.IsOpen()) {
            Console.WriteLine("could not open /dev/i2c-1 — I2C enabled? permissions?")
            return
        }

        let found: List<int> = bus.Scan()     // probe 0x03..0x77
        if (found.Count() == 0) {
            Console.WriteLine("no devices on bus " + String_FromInt(busNum))
        } else {
            Console.WriteLine(String_FromInt(found.Count()) + " device(s):")
            for addr in found {
                Console.WriteLine("  0x" + Program.Hex2(addr))
            }
        }

        bus.Close()
    }
}

Run

amc build main.am -o i2c_scan
./i2c_scan

You'll see something like:

1 device(s):
  0x68

An MPU-6050 shows up at 0x68, a PCF8574 LCD backpack at 0x27, many OLEDs at 0x3c, and so on.

Reading a register

Once you know an address, read or write its registers. For example, to wake an MPU-6050 (clear its PWR_MGMT_1 register at 0x6B) and then burst-read 6 bytes of accelerometer data:

bus.WriteReg(0x68, 0x6B, 0x00)             // wake the device
let raw: List<int> = bus.ReadBytes(0x68, 6) // ACCEL_X/Y/Z high+low bytes

The I²C API at a glance:

Bytes cross the boundary as List<int> (each 0..255).

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