====== Erlang Language Lab ======

===== General Description =====

The main purpose of this exercise is to make a control system similar to the one from the [[c_proj|C programming exercise]].
It should read the values of the induction motor current, calculate RMS and detect the
overload (when RMS exceeds some given value). 
It should also provide self-diagnostics which make sure that data is read correctly.

Skills:
  * Reading data from a file.
  * Data processing.
  * Handling multiple processes (watchdog) and simple message passing.

Grading: points are given in square brackets.

===== Details ======

==== 1. Reading Data ====

  * Using your experience from previous labs, write a function which reads data from {{:cso:ac_current.dat}} and counts the number of samples.
 
==== 2. Simple diagnostic system ====

  * Write a function which reads data from a file {{:cso:ac_current.dat}} [2].
  * Write a function which calculates the RMS value from 20 consecutive samples (in this case it is the main period of the waveform) [6].
  * Make the above functions work together, displaying the calculated RMS value [3].

==== 3. Implementation of "the protection" ====

  * Using the previous functions, write a function which reads data from a file, calculates the RMS value, checks if this value exceeds some given level //x// (given as an argument), and exits if it does so [4]. The function should return the number of the RMS values read before it exits [4] and the violating RMS value as well [2].
  

==== 4. Watchdog ====

A //watchdog// is a process which makes sure that other processes work properly.
It is often used to make sure that data from sensors is read.

Enhance your program to accommodate a watchdog.

Hints:
  * Spawn a watchdog process [2].
  * Make the reading function to send a message to the watchdog every time a new value is read [4].
  * If the watchdog waits for a message too long it should display a message: 'Input data flow is too slow at index:' [4] followed by the index value [2].
  * There should be a way to terminate the watchdog by sending it //a special// message [2].