The server code requires the following libraries from the CircuitPython Bundle:

  • adafruit_ble
  • adafruit_bluefruit_connect
The code for this project needs extensive revision due to changes in CircuitPython. Sorry!

The latest version can be obtained from the Adafruit CircuitPython BLE repo.

Plug in one Feather nRF52840 to your computer via a known good USB data + power cable. The board should show up as a disk drive named CIRCUITPY. Use this guide to update CircuitPython - you will want the latest version 5.0 or above.

Download and copy the two aforementioned libraries to the lib folder on the Feather.

Here's the server code for the BLE peripheral. Click the download link and save to your computer. Then copy the file to on the Feather.

from time import sleep
from adafruit_ble.uart_server import UARTServer
from adafruit_bluefruit_connect.packet import Packet
from adafruit_bluefruit_connect.button_packet import ButtonPacket
from adafruit_bluefruit_connect.color_packet import ColorPacket
from board import A0, D13
from analogio import AnalogIn
from digitalio import DigitalInOut, Direction

led = AnalogIn(A0)  # Initialize blue LED light detector

solenoid = DigitalInOut(D13)  # Initialize solenoid
solenoid.direction = Direction.OUTPUT
solenoid.value = False

uart_server = UARTServer()

while True:
    uart_server.start_advertising()  # Advertise when not connected.

    while not uart_server.connected:  # Wait for connection

    while uart_server.connected:  # Connected
        if uart_server.in_waiting:  # Check BLE commands
            packet = Packet.from_stream(uart_server)
            if isinstance(packet, ButtonPacket):
                if packet.button == '1' and packet.pressed:
                    solenoid.value = True  # Activate solenoid for 1 second
                    solenoid.value = False

        led_intensity = led.value  # Check blue LED detector intensity
        led_on = led_intensity > 1000
        # Color: red = off, green = on
        color_packet = ColorPacket((255 * int(not led_on), 255 * led_on, 0))
            uart_server.write(color_packet.to_bytes())  # Transmit state color
        except OSError:


This guide was first published on Oct 16, 2019. It was last updated on Oct 16, 2019.

This page (Server Code) was last updated on Oct 07, 2021.

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