Specs

bus_names() :: [binary()]

Return a list of available I2C bus names. If nothing is returned, it's possible that the kernel driver for that I2C bus is not enabled or the kernel's device tree is not configured. On Raspbian, run raspi-config and look in the advanced options.

iex> Circuits.I2C.bus_names()
["i2c-1"]

Specs

close(bus()) :: :ok

close the I2C bus

Convenience method to scan all I2C buses for devices

This is only intended to be called from the IEx prompt. Programs should use detect_devices/1.

Specs

detect_devices(bus() | binary()) :: [address()] | {:error, term()}

Scan the I2C bus for devices by performing a read at each device address and returning a list of device addresses that respond.

WARNING: This is intended to be a debugging aid. Reading bytes from devices can advance internal state machines and might cause them to get out of sync with other code.

iex> Circuits.I2C.detect_devices("i2c-1")
[4]

The return value is a list of device addresses that were detected on the specified I2C bus. If you get back 'Hh' or other letters, then IEx converted the list to an Erlang string. Run i v() to get information about the return value and look at the raw string representation for addresses.

If you already have a reference to an open device, then you may pass its reference to detect_devices/1 instead.

Specs

info() :: map()

Return info about the low level I2C interface

This may be helpful when debugging I2C issues.

Specs

open(binary() | charlist()) :: {:ok, bus()} | {:error, term()}

Open an I2C bus

I2C bus names depend on the platform. Names are of the form "i2c-n" where the "n" is the bus number. The correct bus number can be found in the documentation for the device or on a schematic. Another option is to call Circuits.I2C.bus_names/0 to list them for you.

I2c buses may be opened more than once. There is no need to share an I2C bus reference between modules.

On success, this returns a reference to the I2C bus. Use the reference in subsequent calls to read and write I2C devices

Specs

read(bus(), address(), pos_integer(), [opt()]) ::
  {:ok, binary()} | {:error, term()}

Initiate a read transaction to the I2C device at the specified address

Options:

• :retries - number of retries before failing (defaults to no retries)

Specs

read!(bus(), address(), pos_integer(), [opt()]) :: binary()

Initiate a read transaction and raise on error

Specs

write(bus(), address(), iodata(), [opt()]) :: :ok | {:error, term()}

Write data to the I2C device at address.

Options:

• :retries - number of retries before failing (defaults to no retries)

Specs

write!(bus(), address(), iodata(), [opt()]) :: :ok

Write data to the I2C device at address and raise on error

Options:

• :retries - number of retries before failing (defaults to no retries)

Specs

write_read(bus(), address(), iodata(), pos_integer(), [opt()]) ::
  {:ok, binary()} | {:error, term()}

Write data to an I2C device and then immediately issue a read.

This function is useful for devices that want you to write the "register" location to them first and then issue a read to get its contents. Many devices operate this way and this function will issue the commands back-to-back on the I2C bus. Some I2C devices actually require that the read immediately follows the write. If the target supports this, the I2C transaction will be issued that way. On the Raspberry Pi, this can be enabled globally with File.write!("/sys/module/i2c_bcm2708/parameters/combined", "1")

Options:

• :retries - number of retries before failing (defaults to no retries)

Specs

write_read!(bus(), address(), iodata(), pos_integer(), [opt()]) :: binary()

Write data to an I2C device and then immediately issue a read. Raise on errors.

Options:

• :retries - number of retries before failing (defaults to no retries)