Built-in objects · Volt docs

These are always there: no declaration, no import. Call them as wifi.connect(…), system.uptime(), log(…).

`wifi`

Joins a Wi-Fi network. Using it also tells the compiler that analog pins on ADC2 won’t work.

wifi.connect(ssid: string, password: string)

Joins a network. It can fail, so give it an or fallback.
wifi.disconnect()

Leaves the network.
wifi.is_connected() -> bool

Whether the board is on the network.
wifi.get_ip() -> string

The board’s IP address, as text.
wifi.get_rssi() -> int

Signal strength in dBm (closer to 0 is stronger).

Publishes and subscribes to an MQTT broker.

mqtt.connect(url: string)

Connects to a broker, e.g. "mqtt://broker.local". Give it an or fallback.
mqtt.disconnect()

Disconnects from the broker.
mqtt.send(topic: string, data: string)

Publishes text to a topic.
mqtt.send_float(topic: string, value: float)

Publishes a number to a topic.
mqtt.send_int(topic: string, value: int)

Publishes a whole number to a topic.
mqtt.on_receive(topic: string)

Subscribes to a topic.
mqtt.is_connected() -> bool

Whether the broker connection is up.
mqtt.has_message() -> bool

Whether an unread message has arrived.
mqtt.payload() -> string

The latest message’s text, and marks it read.
mqtt.topic() -> string

The topic the latest message came on.

Makes HTTP requests.

http.get(url: string) -> string

Fetches a URL and returns the body (empty on failure, cut at 1023 characters).
http.post(url: string, body: string) -> string

Posts a body to a URL and returns the response body.

Keeps values in flash, so they survive a restart. See Storage in the language guide.

storage.save(key: string, value: any)

Saves a value under a key. Writes are batched to flash within 30 seconds, or at once with flush().
storage.load(key: string) -> int

Loads a whole number saved under a key (0 if there is none).
storage.load_float(key: string) -> float

Loads a number saved under a key.
storage.load_str(key: string) -> string

Loads text saved under a key.
storage.push(list_name: string, value: int)

Appends a value to a named list kept in flash (up to 8 lists of 64 values).
storage.drain(list_name: string) -> int

Takes the oldest value off a named list.
storage.list_count(list_name: string) -> int

How many values a named list holds.
storage.list_clear(list_name: string)

Empties a named list.
storage.flush()

Writes pending saves to flash now.

The board itself: restarting, uptime, memory, the watchdog.

system.restart()

Reboots the board.
system.id() -> int

The chip’s unique ID.
system.uptime() -> int

Seconds since the board started.
system.free_heap() -> int

Free memory, in bytes.
system.micros() -> int

Microseconds since the board started (wraps after about 71 minutes).
system.min_free_heap() -> int

The least free memory seen since the board started.
system.watchdog_enable(timeout_ms: int)

Reboots the board if watchdog_feed() isn’t called within timeout_ms.
system.watchdog_feed()

Resets the watchdog’s countdown.
system.watchdog_disable()

Turns the watchdog off.

Bluetooth Low Energy: advertising, values a phone can read, scanning.

ble.advertise(name: string)

Starts advertising under a name.
ble.stop()

Stops Bluetooth.
ble.is_connected() -> bool

Whether a phone or computer is connected.
ble.expose_int(name: string, value: int) -> int

Publishes a readable value and returns its id, for update_int.
ble.expose_float(name: string, value: float) -> int

Publishes a readable value and returns its id, for update_float.
ble.expose_string(name: string, value: string) -> int

Publishes a readable value and returns its id, for update_string.
ble.update_int(id: int, value: int)

Changes a published value.
ble.update_float(id: int, value: float)

Changes a published value.
ble.update_string(id: int, value: string)

Changes a published value.
ble.scan(duration: Duration) -> int

Scans for nearby devices for duration and returns how many were found.
ble.scan_name(index: int) -> string

The name of a device found by the last scan.
ble.scan_rssi(index: int) -> int

The signal strength of a device found by the last scan.

Firmware updates over the network.

Every channel you declare (channel events: int[8]) has these methods.

events.send(value: any)

Puts a value in the channel. If the channel is full, the value is dropped.
events.receive() -> int

Takes the oldest value out, or returns 0 when the channel is empty. It never waits.
events.try_receive() -> int

The same as receive.
events.count() -> int

How many values are waiting.
events.has_data() -> bool

Whether a value is waiting.
events.is_empty() -> bool

Whether no value is waiting.
events.is_full() -> bool

Whether the buffer is full, so a send would be dropped.
events.clear()

Drops every waiting value.

A UART you declare in the hardware block (uart modem(tx: 17, rx: 16, baud: 9600)) has these methods.

log(tag: string, message: string)

Prints a line to the serial console: the time since boot, the tag, and the message.
sleep(duration: Duration)

Pauses this block for duration; other tasks keep running.
deep_sleep(duration: Duration)

Powers down for duration, then restarts from the beginning. RAM is lost; storage survives.
light_sleep(duration: Duration)

Sleeps for duration and carries on where it left off.
float(value: int) -> float

Converts a whole number to a number with a fraction.
int(value: float) -> int

Converts a number to a whole number, dropping the fraction.
len(text: string) -> int

The length of a string.
contains(text: string, part: string) -> bool

Whether part appears in text.
starts_with(text: string, prefix: string) -> bool

Whether text begins with prefix.
ends_with(text: string, suffix: string) -> bool

Whether text ends with suffix.
to_int(text: string) -> int

Reads a whole number from text.
to_float(text: string) -> float

Reads a number from text.