Hardware Blocks

Blocks that connect to hardware in Flojoy follow a common pattern.

There must always be an “open” block, which creates and persists a hardware connection. Other instrument blocks can then have the required hardware connection injected into the parameters for interfacing with the instrument.

Creating the “Open” block

The “open” block always follows the same template, the following is a minimal example for serial devices:

import serial
from typing import Optional
from flojoy import SerialDevice, flojoy, DataContainer
from flojoy.connection_manager import DeviceConnectionManager

@flojoy(deps={"pyserial": "3.5"})
def OPEN_SERIAL(device: SerialDevice, baudrate: int = 9600) -> String:
    ser = serial.Serial(
        port=device.get_port(),
        baudrate=baudrate,
    )

    DeviceConnectionManager.register_connection(device, ser)

    return None

The “open” blocks must take in a device parameter, which allow you to select from a list of connected devices in the block parameters. The connection is then created, and registered in the DeviceConnectionManager along with its device. This allows the connection to be tied to a specific device for usage later.

Using the connection in blocks

A short example using a serial connection to read some data:

from typing import Optional

import numpy as np
import serial
from flojoy import OrderedPair, SerialDevice, flojoy


@flojoy(deps={"pyserial": "3.5"}, inject_connection=True)
def SERIAL_SINGLE_MEASUREMENT(
    connection: SerialConnection,
    default: Optional[OrderedPair] = None,
) -> OrderedPair:
    ser = connection.get_handle()

    s = ""
    while not s:
        s = ser.readline().decode()

    reading = s[:-2].split(",")
    reading = np.array(reading)
    reading = reading.astype("float64")
    x = np.arange(0, reading.size)

    return OrderedPair(x=x, y=reading)

Once the connection is created by the open block, we can then use it in other blocks by taking in a SerialConnection. We do this by passing inject_connection=True to the flojoy decorator, so that it is automatically passed to the block at runtime. get_handle can then be called on the object to get the underlying connection object.

The SerialConnection parameter must have exactly the name connection.

Note that Connection objects are different from the Device objects.

Connection objects represent an open hardware connection to a device, and are used in blocks that perform operations that use that connection.

Device objects represent information for a connected hardware device, and are only used in “open” blocks as discussed in the previous section.