Python - Dual Relay Bricklet

This is the description of the Python API bindings for the Dual Relay Bricklet. General information and technical specifications for the Dual Relay Bricklet are summarized in its hardware description.

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

Examples

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

Simple

Download (example_simple.py)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
#!/usr/bin/env python
# -*- coding: utf-8 -*-

HOST = "localhost"
PORT = 4223
UID = "XYZ" # Change XYZ to the UID of your Dual Relay Bricklet

import time

from tinkerforge.ip_connection import IPConnection
from tinkerforge.bricklet_dual_relay import BrickletDualRelay

if __name__ == "__main__":
    ipcon = IPConnection() # Create IP connection
    dr = BrickletDualRelay(UID, ipcon) # Create device object

    ipcon.connect(HOST, PORT) # Connect to brickd
    # Don't use device before ipcon is connected

    # Turn relays alternating on/off 10 times with 1 second delay
    for i in range(5):
        time.sleep(1)
        dr.set_state(True, False)
        time.sleep(1)
        dr.set_state(False, True)

    raw_input("Press key to exit\n") # Use input() in Python 3
    ipcon.disconnect()

API

Generally, every method of the Python bindings can throw an tinkerforge.ip_connection.Error exception that has a value and a description property. value can have different values:

  • Error.TIMEOUT = -1
  • Error.ALREADY_CONNECTED = -7
  • Error.NOT_CONNECTED = -8
  • Error.INVALID_PARAMETER = -9
  • Error.NOT_SUPPORTED = -10
  • Error.UNKNOWN_ERROR_CODE = -11
  • Error.STREAM_OUT_OF_SYNC = -12

All methods listed below are thread-safe.

Basic Functions

BrickletDualRelay(uid, ipcon)
Parameters:
  • uid -- string
  • ipcon -- IPConnection

Creates an object with the unique device ID uid:

dual_relay = BrickletDualRelay("YOUR_DEVICE_UID", ipcon)

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

BrickletDualRelay.set_state(relay1, relay2)
Parameters:
  • relay1 -- bool
  • relay2 -- bool
Return type:

None

Sets the state of the relays, true means on and false means off. For example: (true, false) turns relay 1 on and relay 2 off.

If you just want to set one of the relays and don't know the current state of the other relay, you can get the state with get_state() or you can use set_selected_state().

Running monoflop timers will be overwritten if this function is called.

The default value is (false, false).

BrickletDualRelay.get_state()
Return type:(bool, bool)

Returns the state of the relays, true means on and false means off.

The returned namedtuple has the variables relay1 and relay2.

Advanced Functions

BrickletDualRelay.set_monoflop(relay, state, time)
Parameters:
  • relay -- int
  • state -- bool
  • time -- int
Return type:

None

The first parameter can be 1 or 2 (relay 1 or relay 2). The second parameter is the desired state of the relay (true means on and false means off). The third parameter indicates the time (in ms) that the relay should hold the state.

If this function is called with the parameters (1, true, 1500): Relay 1 will turn on and in 1.5s it will turn off again.

A monoflop can be used as a failsafe mechanism. For example: Lets assume you have a RS485 bus and a Dual Relay Bricklet connected to one of the slave stacks. You can now call this function every second, with a time parameter of two seconds. The relay will be on all the time. If now the RS485 connection is lost, the relay will turn off in at most two seconds.

BrickletDualRelay.get_monoflop(relay)
Parameters:relay -- int
Return type:(bool, int, int)

Returns (for the given relay) the current state and the time as set by set_monoflop() as well as the remaining time until the state flips.

If the timer is not running currently, the remaining time will be returned as 0.

The returned namedtuple has the variables state, time and time_remaining.

BrickletDualRelay.set_selected_state(relay, state)
Parameters:
  • relay -- int
  • state -- bool
Return type:

None

Sets the state of the selected relay (1 or 2), true means on and false means off.

The other relay remains untouched.

BrickletDualRelay.get_api_version()
Return type:[int, int, int]

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.

BrickletDualRelay.get_response_expected(function_id)
Parameters:function_id -- int
Return type:bool

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 set_response_expected(). 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 set_response_expected() for the list of function ID constants available for this function.

BrickletDualRelay.set_response_expected(function_id, response_expected)
Parameters:
  • function_id -- int
  • response_expected -- bool
Return type:

None

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:

  • BrickletDualRelay.FUNCTION_SET_STATE = 1
  • BrickletDualRelay.FUNCTION_SET_MONOFLOP = 3
  • BrickletDualRelay.FUNCTION_SET_SELECTED_STATE = 6
BrickletDualRelay.set_response_expected_all(response_expected)
Parameters:response_expected -- bool
Return type:None

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

BrickletDualRelay.get_identity()
Return type:(str, str, chr, [int, int, int], [int, int, int], int)

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 namedtuple has the variables uid, connected_uid, position, hardware_version, firmware_version and device_identifier.

Callback Configuration Functions

BrickletDualRelay.register_callback(callback_id, function)
Parameters:
  • callback_id -- int
  • function -- callable
Return type:

None

Registers the given function with the given callback_id.

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

Callbacks

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

def my_callback(param):
    print(param)

dual_relay.register_callback(BrickletDualRelay.CALLBACK_EXAMPLE, my_callback)

The available constants with inherent number and 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.

BrickletDualRelay.CALLBACK_MONOFLOP_DONE
Parameters:
  • relay -- int
  • state -- bool

This callback is triggered whenever a monoflop timer reaches 0. The parameter contain the relay (1 or 2) and the current state of the relay (the state after the monoflop).

Constants

BrickletDualRelay.DEVICE_IDENTIFIER

This constant is used to identify a Dual Relay Bricklet.

The get_identity() function and the CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

BrickletDualRelay.DEVICE_DISPLAY_NAME

This constant represents the human readable name of a Dual Relay Bricklet.