GrovePi

v0.6.1

GrovePi v0.6.1 GrovePi.Potentiometer View Source

Conveniences for reading from a potentiometer or rotary angle sensor.

Listen for events from a GrovePi potentiometer or rotary angle sensor. There is only one type of event by default; :changed. When registering for an event the potentiometer will send a message similar to {pin, :changed, {value: 1} with the value being a number from 0-1023 that maps to 0 to 5 volts. The potentiometer works by polling GrovePi.Analog on the pin that you have registered to a potentiometer.

Example usage:

iex> {:ok, potentiometer} = GrovePi.Potentiometer.start_link(16)
:ok
iex> GrovePi.Potentiometer.subscribe(16, :changed)
:ok

The GrovePi.Potentiometer.DefaultTrigger is written so when the value of the potentiometer changes, the subscribed process will receive a message in the form of {pid, :changed, %{value: value}. The message should be received using GenServer handle_info/2.

For example:

def handle_info({_pid, :changed, %{value: value}}, state) do
  # do something with `value`
  {:noreply, state}
end

Link to this section Summary

Functions

change_polling(pin, interval, prefix \\ Default)

Stops the current scheduled polling event and starts a new one with the new interval

child_spec(arg)

Returns a specification to start this module under a supervisor

init(list)

Invoked when the server is started. start_link/3 or start/3 will block until it returns

read(pin, prefix \\ Default)

Read the value from the specified pin

read_value(prefix, pin)

Callback implementation for GrovePi.Poller.read_value/2

start_link(pin, opts \\ [])

Starts a process linked to the current process

stop_polling(pin, prefix \\ Default)

Stops polling immediately

subscribe(pin, event, prefix \\ Default)

Subscribes the current process to an event

Link to this section Functions

Link to this function change_polling(pin, interval, prefix \\ Default) View Source 
change_polling(GrovePi.pin(), integer(), atom()) :: :ok

Stops the current scheduled polling event and starts a new one with the new interval.

Link to this function child_spec(arg) View Source

Returns a specification to start this module under a supervisor.

See Supervisor.

Link to this function init(list) View Source

Invoked when the server is started. start_link/3 or start/3 will block until it returns.

args is the argument term (second argument) passed to start_link/3.

Returning {:ok, state} will cause start_link/3 to return {:ok, pid} and the process to enter its loop.

Returning {:ok, state, timeout} is similar to {:ok, state} except handle_info(:timeout, state) will be called after timeout milliseconds if no messages are received within the timeout.

Returning {:ok, state, :hibernate} is similar to {:ok, state} except the process is hibernated before entering the loop. See c:handle_call/3 for more information on hibernation.

Returning {:ok, state, {:continue, continue}} is similar to {:ok, state} except that immediately after entering the loop the c:handle_continue/2 callback will be invoked with the value continue as first argument.

Returning :ignore will cause start_link/3 to return :ignore and the process will exit normally without entering the loop or calling c:terminate/2. If used when part of a supervision tree the parent supervisor will not fail to start nor immediately try to restart the GenServer. The remainder of the supervision tree will be started and so the GenServer should not be required by other processes. It can be started later with Supervisor.restart_child/2 as the child specification is saved in the parent supervisor. The main use cases for this are:

  • The GenServer is disabled by configuration but might be enabled later.
  • An error occurred and it will be handled by a different mechanism than the Supervisor. Likely this approach involves calling Supervisor.restart_child/2 after a delay to attempt a restart.

Returning {:stop, reason} will cause start_link/3 to return {:error, reason} and the process to exit with reason reason without entering the loop or calling c:terminate/2.

Callback implementation for GenServer.init/1.

Link to this function read(pin, prefix \\ Default) View Source 
read(GrovePi.pin(), atom()) :: GrovePi.Analog.adc_level()

Read the value from the specified pin.

Link to this function read_value(prefix, pin) View Source

Callback implementation for GrovePi.Poller.read_value/2.

Link to this function start_link(pin, opts \\ []) View Source

Starts a process linked to the current process.

This is often used to start the process as part of a supervision tree.

Options

  • :poll_interval - The time in ms between polling for state.i If set to 0 polling will be turned off. Default: 100
  • :trigger - This is used to pass in a trigger to use for triggering events. See specific poller for defaults
  • :trigger_opts - This is used to pass options to a trigger init1. The default is []
Link to this function stop_polling(pin, prefix \\ Default) View Source 
stop_polling(GrovePi.pin(), atom()) :: :ok

Stops polling immediately

Link to this function subscribe(pin, event, prefix \\ Default) View Source 
subscribe(GrovePi.pin(), GrovePi.Trigger.event(), atom()) ::
  {:ok, pid()} | {:error, {:already_registered, pid()}}

Subscribes the current process to an event.