MQTT - Solid State Relay Bricklet

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

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


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


Download (example-simple.txt)

# Change XYZ to the UID of your Solid State Relay Bricklet

    # Turn relay on/off 10 times with 1 second delay
    for i in 0..4

        wait for 1s

        publish '{"state": true}' to tinkerforge/request/solid_state_relay_bricklet/XYZ/set_state

        wait for 1s

        publish '{"state": false}' to tinkerforge/request/solid_state_relay_bricklet/XYZ/set_state



All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as member _ERROR. It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

  • state – Type: bool, Default: false
  • no response

Sets the state of the relays true means on and false means off.

A running monoflop timer will be aborted if this function is called.

  • empty payload
  • state – Type: bool, Default: false

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

Advanced Functions

  • state – Type: bool
  • time – Type: int, Unit: 1 ms, Range: [0 to 232 - 1]
  • no response

The first parameter is the desired state of the relay (true means on and false means off). The second parameter indicates the time that the relay should hold the state.

If this function is called with the parameters (true, 1500): The relay 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 Solid State 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.

  • empty payload
  • state – Type: bool
  • time – Type: int, Unit: 1 ms, Range: [0 to 232 - 1]
  • time_remaining – Type: int, Unit: 1 ms, Range: [0 to 232 - 1]

Returns the current state and the time as set by request/solid_state_relay_bricklet/<UID>/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.

  • empty payload
  • uid – Type: string, Length: up to 8
  • connected_uid – Type: string, Length: up to 8
  • position – Type: char, Range: ["a" to "h", "i", "z"]
  • hardware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]
  • firmware_version – Type: [int, ...], Length: 3
    • 0: major – Type: int, Range: [0 to 255]
    • 1: minor – Type: int, Range: [0 to 255]
    • 2: revision – Type: int, Range: [0 to 255]
  • device_identifier – Type: int, Range: [0 to 216 - 1]
  • _display_name – Type: string

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', 'd', 'e', 'f', 'g' or 'h' (Bricklet Port). The Raspberry Pi HAT (Zero) Brick is always at position 'i' and the Bricklet connected to an Isolator Bricklet is always as position 'z'.

The device identifier numbers can be found here. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the Solid State Relay's name in a human readable form.


Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.


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.

Register Request:
  • register – Type: bool
Callback Response:
  • state – Type: bool

A callback can be registered for this event by publishing to the .../register/solid_state_relay_bricklet/<UID>/monoflop_done[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/solid_state_relay_bricklet/<UID>/monoflop_done[/<SUFFIX>] topic for each registered suffix.

This callback is triggered whenever the monoflop timer reaches 0. The parameter is the current state of the relay (the state after the monoflop).