PHP - Load Cell Bricklet

This is the description of the PHP API bindings for the Load Cell Bricklet. General information and technical specifications for the Load Cell Bricklet are summarized in its hardware description.

An installation guide for the PHP API bindings is part of their general description.

Examples

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

Simple

Download (ExampleSimple.php)

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<?php

require_once('Tinkerforge/IPConnection.php');
require_once('Tinkerforge/BrickletLoadCell.php');

use Tinkerforge\IPConnection;
use Tinkerforge\BrickletLoadCell;

const HOST = 'localhost';
const PORT = 4223;
const UID = 'XYZ'; // Change XYZ to the UID of your Load Cell Bricklet

$ipcon = new IPConnection(); // Create IP connection
$lc = new BrickletLoadCell(UID, $ipcon); // Create device object

$ipcon->connect(HOST, PORT); // Connect to brickd
// Don't use device before ipcon is connected

// Get current weight
$weight = $lc->getWeight();
echo "Weight: $weight g\n";

echo "Press key to exit\n";
fgetc(fopen('php://stdin', 'r'));
$ipcon->disconnect();

?>

Callback

Download (ExampleCallback.php)

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<?php

require_once('Tinkerforge/IPConnection.php');
require_once('Tinkerforge/BrickletLoadCell.php');

use Tinkerforge\IPConnection;
use Tinkerforge\BrickletLoadCell;

const HOST = 'localhost';
const PORT = 4223;
const UID = 'XYZ'; // Change XYZ to the UID of your Load Cell Bricklet

// Callback function for weight callback
function cb_weight($weight)
{
    echo "Weight: $weight g\n";
}

$ipcon = new IPConnection(); // Create IP connection
$lc = new BrickletLoadCell(UID, $ipcon); // Create device object

$ipcon->connect(HOST, PORT); // Connect to brickd
// Don't use device before ipcon is connected

// Register weight callback to function cb_weight
$lc->registerCallback(BrickletLoadCell::CALLBACK_WEIGHT, 'cb_weight');

// Set period for weight callback to 1s (1000ms)
// Note: The weight callback is only called every second
//       if the weight has changed since the last call!
$lc->setWeightCallbackPeriod(1000);

echo "Press ctrl+c to exit\n";
$ipcon->dispatchCallbacks(-1); // Dispatch callbacks forever

?>

Threshold

Download (ExampleThreshold.php)

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<?php

require_once('Tinkerforge/IPConnection.php');
require_once('Tinkerforge/BrickletLoadCell.php');

use Tinkerforge\IPConnection;
use Tinkerforge\BrickletLoadCell;

const HOST = 'localhost';
const PORT = 4223;
const UID = 'XYZ'; // Change XYZ to the UID of your Load Cell Bricklet

// Callback function for weight reached callback
function cb_weightReached($weight)
{
    echo "Weight: $weight g\n";
}

$ipcon = new IPConnection(); // Create IP connection
$lc = new BrickletLoadCell(UID, $ipcon); // Create device object

$ipcon->connect(HOST, PORT); // Connect to brickd
// Don't use device before ipcon is connected

// Get threshold callbacks with a debounce time of 1 second (1000ms)
$lc->setDebouncePeriod(1000);

// Register weight reached callback to function cb_weightReached
$lc->registerCallback(BrickletLoadCell::CALLBACK_WEIGHT_REACHED, 'cb_weightReached');

// Configure threshold for weight "greater than 200 g"
$lc->setWeightCallbackThreshold('>', 200, 0);

echo "Press ctrl+c to exit\n";
$ipcon->dispatchCallbacks(-1); // Dispatch callbacks forever

?>

API

Functions that return multiple values return them in an associative array.

Basic Functions

class BrickletLoadCell(string $uid, IPConnection $ipcon)

Creates an object with the unique device ID $uid:

<?php   $load_cell = new BrickletLoadCell('YOUR_DEVICE_UID', $ipcon);   ?>

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

int BrickletLoadCell::getWeight()

Returns the currently measured weight in grams.

If you want to get the weight periodically, it is recommended to use the CALLBACK_WEIGHT callback and set the period with setWeightCallbackPeriod().

void BrickletLoadCell::ledOn()

Turns the LED on.

void BrickletLoadCell::ledOff()

Turns the LED off.

bool BrickletLoadCell::isLEDOn()

Returns true if the led is on, false otherwise.

void BrickletLoadCell::tare()

Sets the currently measured weight as tare weight.

Advanced Functions

void BrickletLoadCell::setMovingAverage(int $average)

Sets the length of a moving averaging for the weight value.

Setting the length to 1 will turn the averaging off. With less averaging, there is more noise on the data.

The range for the averaging is 1-40.

The default value is 4.

int BrickletLoadCell::getMovingAverage()

Returns the length moving average as set by setMovingAverage().

void BrickletLoadCell::calibrate(int $weight)

To calibrate your Load Cell Bricklet you have to

  • empty the scale and call this function with 0 and
  • add a known weight to the scale and call this function with the weight in grams.

The calibration is saved in the EEPROM of the Bricklet and only needs to be done once.

We recommend to use the Brick Viewer for calibration, you don't need to call this function in your source code.

void BrickletLoadCell::setConfiguration(int $rate, int $gain)

The measurement rate and gain are configurable.

The rate can be either 10Hz or 80Hz. A faster rate will produce more noise. It is additionally possible to add a moving average (see setMovingAverage()) to the measurements.

The gain can be 128x, 64x or 32x. It represents a measurement range of ±20mV, ±40mV and ±80mV respectively. The Load Cell Bricklet uses an excitation voltage of 5V and most load cells use an output of 2mV/V. That means the voltage range is ±15mV for most load cells (i.e. gain of 128x is best). If you don't know what all of this means you should keep it at 128x, it will most likely be correct.

The configuration is saved in the EEPROM of the Bricklet and only needs to be done once.

We recommend to use the Brick Viewer for configuration, you don't need to call this function in your source code.

The default rate is 10Hz and the default gain is 128x.

The following constants are available for this function:

  • BrickletLoadCell::RATE_10HZ = 0
  • BrickletLoadCell::RATE_80HZ = 1
  • BrickletLoadCell::GAIN_128X = 0
  • BrickletLoadCell::GAIN_64X = 1
  • BrickletLoadCell::GAIN_32X = 2
array BrickletLoadCell::getConfiguration()

Returns the configuration as set by setConfiguration().

The following constants are available for this function:

  • BrickletLoadCell::RATE_10HZ = 0
  • BrickletLoadCell::RATE_80HZ = 1
  • BrickletLoadCell::GAIN_128X = 0
  • BrickletLoadCell::GAIN_64X = 1
  • BrickletLoadCell::GAIN_32X = 2

The returned array has the keys rate and gain.

array BrickletLoadCell::getAPIVersion()

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.

bool BrickletLoadCell::getResponseExpected(int $function_id)

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.

void BrickletLoadCell::setResponseExpected(int $function_id, bool $response_expected)

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:

  • BrickletLoadCell::FUNCTION_SET_WEIGHT_CALLBACK_PERIOD = 2
  • BrickletLoadCell::FUNCTION_SET_WEIGHT_CALLBACK_THRESHOLD = 4
  • BrickletLoadCell::FUNCTION_SET_DEBOUNCE_PERIOD = 6
  • BrickletLoadCell::FUNCTION_SET_MOVING_AVERAGE = 8
  • BrickletLoadCell::FUNCTION_LED_ON = 10
  • BrickletLoadCell::FUNCTION_LED_OFF = 11
  • BrickletLoadCell::FUNCTION_CALIBRATE = 13
  • BrickletLoadCell::FUNCTION_TARE = 14
  • BrickletLoadCell::FUNCTION_SET_CONFIGURATION = 15
void BrickletLoadCell::setResponseExpectedAll(bool $response_expected)

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

array BrickletLoadCell::getIdentity()

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.

The returned array has the keys uid, connected_uid, position, hardware_version, firmware_version and device_identifier.

Callback Configuration Functions

void BrickletLoadCell::registerCallback(int $callback_id, callable $callback, mixed $user_data=NULL)

Registers the given $function with the given $callback_id. The optional $user_data will be passed as the last parameter to the function.

The available callback IDs with corresponding function signatures are listed below.

void BrickletLoadCell::setWeightCallbackPeriod(int $period)

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

The CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

The default value is 0.

int BrickletLoadCell::getWeightCallbackPeriod()

Returns the period as set by setWeightCallbackPeriod().

void BrickletLoadCell::setWeightCallbackThreshold(string $option, int $min, int $max)

Sets the thresholds for the CALLBACK_WEIGHT_REACHED callback.

The following options are possible:

Option Description
'x' Callback is turned off
'o' Callback is triggered when the weight is outside the min and max values
'i' Callback is triggered when the weight is inside the min and max values
'<' Callback is triggered when the weight is smaller than the min value (max is ignored)
'>' Callback is triggered when the weight is greater than the min value (max is ignored)

The default value is ('x', 0, 0).

The following constants are available for this function:

  • BrickletLoadCell::THRESHOLD_OPTION_OFF = 'x'
  • BrickletLoadCell::THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLoadCell::THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLoadCell::THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLoadCell::THRESHOLD_OPTION_GREATER = '>'
array BrickletLoadCell::getWeightCallbackThreshold()

Returns the threshold as set by setWeightCallbackThreshold().

The following constants are available for this function:

  • BrickletLoadCell::THRESHOLD_OPTION_OFF = 'x'
  • BrickletLoadCell::THRESHOLD_OPTION_OUTSIDE = 'o'
  • BrickletLoadCell::THRESHOLD_OPTION_INSIDE = 'i'
  • BrickletLoadCell::THRESHOLD_OPTION_SMALLER = '<'
  • BrickletLoadCell::THRESHOLD_OPTION_GREATER = '>'

The returned array has the keys option, min and max.

void BrickletLoadCell::setDebouncePeriod(int $debounce)

Sets the period in ms with which the threshold callback

is triggered, if the threshold

keeps being reached.

The default value is 100.

int BrickletLoadCell::getDebouncePeriod()

Returns the debounce period as set by setDebouncePeriod().

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the registerCallback() function of the device object. The first parameter is the callback ID and the second parameter the callback function:

<?php

function myCallback($param)
{
    echo $param . "\n";
}

$load_cell->registerCallback(BrickletLoadCell::CALLBACK_EXAMPLE, 'myCallback');

?>

The available constants with corresponding function signatures 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.

int BrickletLoadCell::CALLBACK_WEIGHT
<?php   void callback(int $weight [, mixed $user_data])   ?>

This callback is triggered periodically with the period that is set by setWeightCallbackPeriod(). The parameter is the weight as measured by the load cell.

The CALLBACK_WEIGHT callback is only triggered if the weight has changed since the last triggering.

int BrickletLoadCell::CALLBACK_WEIGHT_REACHED
<?php   void callback(int $weight [, mixed $user_data])   ?>

This callback is triggered when the threshold as set by setWeightCallbackThreshold() is reached. The parameter is the weight as measured by the load cell.

If the threshold keeps being reached, the callback is triggered periodically with the period as set by setDebouncePeriod().

Constants

int BrickletLoadCell::DEVICE_IDENTIFIER

This constant is used to identify a Load Cell Bricklet.

The getIdentity() function and the IPConnection::CALLBACK_ENUMERATE callback of the IP Connection have a deviceIdentifier parameter to specify the Brick's or Bricklet's type.

string BrickletLoadCell::DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Load Cell Bricklet.