Delphi/Lazarus - Hall Effect Bricklet

This is the description of the Delphi/Lazarus API bindings for the Hall Effect Bricklet. General information and technical specifications for the Hall Effect Bricklet are summarized in its hardware description.

An installation guide for the Delphi/Lazarus API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Simple

Download (ExampleSimple.pas)

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program ExampleSimple;

{$ifdef MSWINDOWS}{$apptype CONSOLE}{$endif}
{$ifdef FPC}{$mode OBJFPC}{$H+}{$endif}

uses
  SysUtils, IPConnection, BrickletHallEffect;

type
  TExample = class
  private
    ipcon: TIPConnection;
    he: TBrickletHallEffect;
  public
    procedure Execute;
  end;

const
  HOST = 'localhost';
  PORT = 4223;
  UID = 'XYZ'; { Change XYZ to the UID of your Hall Effect Bricklet }

var
  e: TExample;

procedure TExample.Execute;
var count: longword;
begin
  { Create IP connection }
  ipcon := TIPConnection.Create;

  { Create device object }
  he := TBrickletHallEffect.Create(UID, ipcon);

  { Connect to brickd }
  ipcon.Connect(HOST, PORT);
  { Don't use device before ipcon is connected }

  { Get current edge count without reset }
  count := he.GetEdgeCount(false);
  WriteLn(Format('Count: %d', [count]));

  WriteLn('Press key to exit');
  ReadLn;
  ipcon.Destroy; { Calls ipcon.Disconnect internally }
end;

begin
  e := TExample.Create;
  e.Execute;
  e.Destroy;
end.

Callback

Download (ExampleCallback.pas)

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program ExampleCallback;

{$ifdef MSWINDOWS}{$apptype CONSOLE}{$endif}
{$ifdef FPC}{$mode OBJFPC}{$H+}{$endif}

uses
  SysUtils, IPConnection, BrickletHallEffect;

type
  TExample = class
  private
    ipcon: TIPConnection;
    he: TBrickletHallEffect;
  public
    procedure EdgeCountCB(sender: TBrickletHallEffect; const count: longword;
                          const value: boolean);
    procedure Execute;
  end;

const
  HOST = 'localhost';
  PORT = 4223;
  UID = 'XYZ'; { Change XYZ to the UID of your Hall Effect Bricklet }

var
  e: TExample;

{ Callback procedure for edge count callback }
procedure TExample.EdgeCountCB(sender: TBrickletHallEffect; const count: longword;
                               const value: boolean);
begin
  WriteLn(Format('Count: %d', [count]));
end;

procedure TExample.Execute;
begin
  { Create IP connection }
  ipcon := TIPConnection.Create;

  { Create device object }
  he := TBrickletHallEffect.Create(UID, ipcon);

  { Connect to brickd }
  ipcon.Connect(HOST, PORT);
  { Don't use device before ipcon is connected }

  { Register edge count callback to procedure EdgeCountCB }
  he.OnEdgeCount := {$ifdef FPC}@{$endif}EdgeCountCB;

  { Set period for edge count callback to 0.05s (50ms)
    Note: The edge count callback is only called every 0.05 seconds
          if the edge count has changed since the last call! }
  he.SetEdgeCountCallbackPeriod(50);

  WriteLn('Press key to exit');
  ReadLn;
  ipcon.Destroy; { Calls ipcon.Disconnect internally }
end;

begin
  e := TExample.Create;
  e.Execute;
  e.Destroy;
end.

API

Since Delphi does not support multiple return values directly, we use the out keyword to return multiple values from a function.

All functions and procedures listed below are thread-safe.

Basic Functions

constructor TBrickletHallEffect.Create(const uid: string; ipcon: TIPConnection)

Creates an object with the unique device ID uid:

hallEffect := TBrickletHallEffect.Create('YOUR_DEVICE_UID', ipcon);

This object can then be used after the IP Connection is connected (see examples above).

function TBrickletHallEffect.GetValue: boolean

Returns true if a magnetic field of 35 Gauss (3.5mT) or greater is detected.

function TBrickletHallEffect.GetEdgeCount(const resetCounter: boolean): longword

Returns the current value of the edge counter. You can configure edge type (rising, falling, both) that is counted with SetEdgeCountConfig.

If you set the reset counter to true, the count is set back to 0 directly after it is read.

Advanced Functions

procedure TBrickletHallEffect.SetEdgeCountConfig(const edgeType: byte; const debounce: byte)

The edge type parameter configures if rising edges, falling edges or both are counted. Possible edge types are:

  • 0 = rising (default)
  • 1 = falling
  • 2 = both

A magnetic field of 35 Gauss (3.5mT) or greater causes a falling edge and a magnetic field of 25 Gauss (2.5mT) or smaller causes a rising edge.

If a magnet comes near the Bricklet the signal goes low (falling edge), if a magnet is removed from the vicinity the signal goes high (rising edge).

The debounce time is given in ms.

Configuring an edge counter resets its value to 0.

If you don't know what any of this means, just leave it at default. The default configuration is very likely OK for you.

Default values: 0 (edge type) and 100ms (debounce time)

The following constants are available for this function:

  • BRICKLET_HALL_EFFECT_EDGE_TYPE_RISING = 0
  • BRICKLET_HALL_EFFECT_EDGE_TYPE_FALLING = 1
  • BRICKLET_HALL_EFFECT_EDGE_TYPE_BOTH = 2
procedure TBrickletHallEffect.GetEdgeCountConfig(out edgeType: byte; out debounce: byte)

Returns the edge type and debounce time as set by SetEdgeCountConfig.

The following constants are available for this function:

  • BRICKLET_HALL_EFFECT_EDGE_TYPE_RISING = 0
  • BRICKLET_HALL_EFFECT_EDGE_TYPE_FALLING = 1
  • BRICKLET_HALL_EFFECT_EDGE_TYPE_BOTH = 2
function TBrickletHallEffect.GetAPIVersion: array [0..2] of byte

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

function TBrickletHallEffect.GetResponseExpected(const functionId: byte): boolean

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by SetResponseExpected. For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See SetResponseExpected for the list of function ID constants available for this function.

procedure TBrickletHallEffect.SetResponseExpected(const functionId: byte; const responseExpected: boolean)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID constants are available for this function:

  • BRICKLET_HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CONFIG = 3
  • BRICKLET_HALL_EFFECT_FUNCTION_SET_EDGE_INTERRUPT = 5
  • BRICKLET_HALL_EFFECT_FUNCTION_SET_EDGE_COUNT_CALLBACK_PERIOD = 7
procedure TBrickletHallEffect.SetResponseExpectedAll(const responseExpected: boolean)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

procedure TBrickletHallEffect.GetIdentity(out uid: string; out connectedUid: string; out position: char; out hardwareVersion: array [0..2] of byte; out firmwareVersion: array [0..2] of byte; out deviceIdentifier: word)

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

procedure TBrickletHallEffect.SetEdgeInterrupt(const edges: longword)

Sets the number of edges until an interrupt is invoked.

If edges is set to n, an interrupt is invoked for every n-th detected edge.

If edges is set to 0, the interrupt is disabled.

Default value is 0.

function TBrickletHallEffect.GetEdgeInterrupt: longword

Returns the edges as set by SetEdgeInterrupt.

procedure TBrickletHallEffect.SetEdgeCountCallbackPeriod(const period: longword)

Sets the period in ms with which the OnEdgeCount callback is triggered periodically. A value of 0 turns the callback off.

The OnEdgeCount callback is only triggered if the edge count has changed since the last triggering.

The default value is 0.

function TBrickletHallEffect.GetEdgeCountCallbackPeriod: longword

Returns the period as set by SetEdgeCountCallbackPeriod.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done by assigning a procedure to an callback property of the device object:

procedure TExample.MyCallback(sender: TBrickletHallEffect; const param: word);
begin
  WriteLn(param);
end;

hallEffect.OnExample := {$ifdef FPC}@{$endif}example.MyCallback;

The available callback property and their type of parameters are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

property TBrickletHallEffect.OnEdgeCount
procedure(sender: TBrickletHallEffect; const count: longword; const value: boolean) of object;

This callback is triggered periodically with the period that is set by SetEdgeCountCallbackPeriod. The parameters are the current count and the current value (see GetValue and GetEdgeCount).

The OnEdgeCount callback is only triggered if the count or value changed since the last triggering.

Constants

const BRICKLET_HALL_EFFECT_DEVICE_IDENTIFIER

This constant is used to identify a Hall Effect Bricklet.

The GetIdentity function and the OnEnumerate callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

const BRICKLET_HALL_EFFECT_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Hall Effect Bricklet.