BLE Beacon

Broadcast a fake temperature reading in the advertising packet's manufacturer-data field. This is broadcaster-mode BLE: the device never accepts connections; it just transmits a short payload that any scanner in range can pick up. See the ble API reference for the full type surface.

Useful for presence beacons, simple sensor broadcasts, iBeacon-style advertisers, or anything where you want to avoid the power and complexity of GATT connections.

Hardware

Any ESP32 family board with BLE (ESP32-C3, ESP32-C6, ESP32-S3, original ESP32). ESP32-S2 has no BLE radio and is not supported.
USB cable for flashing and serial logging.
A phone with nRF Connect for Mobile or LightBlue to observe the beacon.

Code

import {ble
, peripheral
} from 'mikro/ble'
import {sleep
} from 'mikro/sleep'

ble
.name
 = 'mikrojs-beacon'

// Encode a fake temperature reading as manufacturer-specific data.
// First two bytes are the company ID (0xFFFF = reserved for testing).
// Remaining bytes are a little-endian int16 in units of 0.01 °C.
function encodeTemperature
(tempCelsius
: number): Uint8Array
 {
  const centi
 = Math
.round
(tempCelsius
 * 100)
  return new Uint8Array
([0xff, 0xff, centi
 & 0xff, (centi
 >> 8) & 0xff])
}

async function startAdvertising
(tempCelsius
: number) {
  return peripheral
.advertise
({
    name
: 'mikrojs-beacon',
    connectable
: false,
    interval
: {min
: 1000, max
: 1500},
    includeTxPower
: true,
    manufacturerData
: encodeTemperature
(tempCelsius
),
  })
}

let temp
 = 21.5
let result
 = await startAdvertising
(temp
)

if (!result
.ok
) {
  console
.error
('ble.advertise failed:', result
.error
)
} else {
  console
.log
('BLE beacon advertising as %s at %s', ble
.name
, ble
.address
)

  while (true) {
    await sleep
(5000)
    temp
 += (Math
.random
() - 0.5) * 0.2
    const stopResult
 = result
.value
.stop
()
    if (!stopResult
.ok
) {
      console
.warn
('ble.stop (refresh) failed:', stopResult
.error
)
    }
    result
 = await startAdvertising
(temp
)
    if (!result
.ok
) {
      console
.error
('ble.advertise (refresh) failed:', result
.error
)
      break
    }
  }
}

What you'll see

In nRF Connect / LightBlue, scan for nearby devices and look for mikrojs-beacon. Tapping into it reveals the advertising payload:

Complete Local Name: mikrojs-beacon
Manufacturer Specific Data: FFFF5308 (or similar). Decoded as:
- First two bytes FFFF = company ID (reserved for testing).
- Next two bytes 5308 = little-endian int16 = 0x0853 = 2131 = 21.31 °C.
TX Power Level: typically 0 or +9 dBm on ESP32-C6's default setting.
RSSI: updates continuously as you move.

Every ~5 seconds the temperature bytes drift slightly as the loop adds random noise.

Create project

pnpmnpmyarnbun

pnpm create mikro --template ble-beacon

npm create mikro -- --template ble-beacon

yarn create mikro --template ble-beacon

bun create mikro --template ble-beacon

Run it

pnpmnpmyarnbun

pnpm install
pnpm mikro flash  # only needed once per board
pnpm mikro dev

npm install
npx mikro flash  # only needed once per board
npx mikro dev

yarn install
yarn mikro flash  # only needed once per board
yarn mikro dev

bun install
bunx mikro flash  # only needed once per board
bunx mikro dev

View source on GitHub

BLE Beacon ​

Hardware ​

Code ​

What you'll see ​