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https://github.com/ekspla/micropython_aioble_examples

A few aioble (asyncio BLE) examples of micropython using esp32
https://github.com/ekspla/micropython_aioble_examples

aioble asyncio ble bluetooth-low-energy esp32 heart-rate hioki micropython multimeter python voltmeter

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A few aioble (asyncio BLE) examples of micropython using esp32

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# micropython_aioble_examples

A few aioble (asyncio bluetooth low energy) examples of Micropython using ESP32



(C) 2023-2024 [ekspla](https://github.com/ekspla/micropython_aioble_examples)



The following examples were tested with [micropython](https://micropython.org/) 1.21.0-1.23.0 and [aioble](https://github.com/micropython/micropython-lib/tree/master/micropython/bluetooth/aioble) on [ESP32-DevKitC-32E](https://www.espressif.com/en/products/devkits/esp32-devkitc).



## Read measured values from a [HIOKI](https://www.hioki.com/) voltmeter via BLE

```hioki_z3210.py```



An example to read measured values from HIOKI's voltmeter, DT4261, via [Z3210 BLE interface](https://www.hioki.com/global/products/specialized-solutions/connecting-instruments/id_6780).

Other mesurement tools of HIOKI equipped with the BLE interface may also work (with/without a bit of modification).

Though the ways (e.g. commands; [references](https://www.hioki.com/global/support/download/software/versionup/detail/id_235) available from their website) to communicate with the tools are similar to those of USB ([DT4900-01](https://www.hioki.com/global/support/download/software/versionup/detail/id_235)), RS232 and GPIB interfaces, 

I found this BLE interface very useful in probing hazardous high voltages/currents at a safe place because of the wireless nature.  



I feel like using a home-built tiny display device equipped with an ESP32 is more convenient than using HIOKI's proprietary software with a smartphone.



```python

MicroPython v1.21.0 on 2023-10-05; Generic ESP32 module with ESP32

Type "help()" for more information.

>>>

>>> import hioki_z3210

>>> hioki_z3210.start()

Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)

Connecting to Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)

Connected.

(2023, 10, 26, 9, 37, 3, 3, 299)        +1.00000000E-04

(2023, 10, 26, 9, 37, 3, 3, 299)        +1.00000000E-04

(2023, 10, 26, 9, 37, 4, 3, 299)        +1.00000000E-04

(2023, 10, 26, 9, 37, 4, 3, 299)        +1.00000000E-04



 ...

 

```



## Read heart rate values from a heart rate sensor via BLE

```hr_read.py```



An example to read heart rate values (BPM) from [Magene's H64](https://support.magene.com/hc/en-us/categories/900000170623-H64-Heart-Rate-Sensor).  

Change the device name ```_HR_SENSOR_NAME``` or the ```address``` to specify your device.  The code should work for most of the BLE heart-rate 

sensors because the service and the characteristics are common.



```python

MicroPython v1.21.0 on 2023-10-05; Generic ESP32 module with ESP32

Type "help()" for more information.

>>>

>>> import hr_read

>>> hr_read.start()

Connecting to Device(ADDR_RANDOM, d8:75:ba:xx:yy:zz)

(2000, 1, 1, 6, 27, 59, 5, 1)	45

(2000, 1, 1, 6, 28, 0, 5, 1)	45

(2000, 1, 1, 6, 28, 1, 5, 1)	45

(2000, 1, 1, 6, 28, 2, 5, 1)	46



 ...



```



## Handling of connections to multiple peripherals and disconnect/reconnect

```conn_multiple.py```



Based on the codes of voltmeter and heart rate monitor, an example is shown.



You may want to change the maximum allowed number of connections in bluetooth stack.  

ESP32_GENERIC ([ESP-IDF](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/kconfig.html)) for example, 

change ```CONFIG_BT_NIMBLE_MAX_CONNECTIONS``` and ```CONFIG_BTDM_CTRL_BLE_MAX_CONN``` in config file (default to 4 and 3, 

respectively). I have changed these (to 5 and 4) and got successfull concurrent connections to 4 peripherals.



If you have to find peripheral devices, write and use a loop of scan/connect/service-discovery to list the target devices in the beginning.

```

Connecting to Device(ADDR_RANDOM, d8:75:ba:xx:yy:zz)             # Heart rate sensor, switched on.

Connected. 

Connecting to Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)             # Voltmeter DT4261, switched off.

(2024, 5, 22, 7, 32, 27, 2, 143)        48 [bpm]

(2024, 5, 22, 7, 32, 29, 2, 143)        48 [bpm]

(2024, 5, 22, 7, 32, 30, 2, 143)        48 [bpm]

(2024, 5, 22, 7, 32, 31, 2, 143)        48 [bpm]

Timeout during connection

(2024, 5, 22, 7, 32, 32, 2, 143)        48 [bpm]

(2024, 5, 22, 7, 32, 34, 2, 143)        48 [bpm]

(2024, 5, 22, 7, 32, 35, 2, 143)        48 [bpm]

Connecting to Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)             # Power on DT4261.

Connected. 

(2024, 5, 22, 7, 32, 37, 2, 143)        47 [bpm]

(2024, 5, 22, 7, 32, 37, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 37, 2, 143)        47 [bpm]

(2024, 5, 22, 7, 32, 38, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 38, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 39, 2, 143)        47 [bpm]

(2024, 5, 22, 7, 32, 39, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 40, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 40, 2, 143)        47 [bpm]

(2024, 5, 22, 7, 32, 40, 2, 143)        DT4261;-1.00000000E-04

(2024, 5, 22, 7, 32, 41, 2, 143)        DT4261;-1.00000000E-04

(2024, 5, 22, 7, 32, 41, 2, 143)        46 [bpm]

(2024, 5, 22, 7, 32, 42, 2, 143)        DT4261;-1.00000000E-04

(2024, 5, 22, 7, 32, 42, 2, 143)        DT4261;-1.00000000E-04

(2024, 5, 22, 7, 32, 43, 2, 143)        46 [bpm]

Error!                                                           # Power off DT4261.

(2024, 5, 22, 7, 32, 44, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 45, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 46, 2, 143)        46 [bpm]

Connecting to Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)

(2024, 5, 22, 7, 32, 48, 2, 143)        46 [bpm]

(2024, 5, 22, 7, 32, 49, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 51, 2, 143)        46 [bpm]

(2024, 5, 22, 7, 32, 52, 2, 143)        45 [bpm]

Timeout during connection

(2024, 5, 22, 7, 32, 53, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 55, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 55, 2, 143)        45 [bpm]

(2024, 5, 22, 7, 32, 57, 2, 143)        45 [bpm]

Connecting to Device(ADDR_PUBLIC, a4:9e:69:xx:yy:zz)             # Power on DT4261 again.

Connected. 

(2024, 5, 22, 7, 32, 58, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 58, 2, 143)        46 [bpm]

(2024, 5, 22, 7, 32, 59, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 32, 59, 2, 143)        DT4261;+0.00000000E+00

(2024, 5, 22, 7, 33, 0, 2, 143)         46 [bpm]

(2024, 5, 22, 7, 33, 0, 2, 143)         DT4261;+0.00000000E+00

(2024, 5, 22, 7, 33, 1, 2, 143)         DT4261;-1.00000000E-04

(2024, 5, 22, 7, 33, 1, 2, 143)         46 [bpm]

(2024, 5, 22, 7, 33, 1, 2, 143)         DT4261;-1.00000000E-04

(2024, 5, 22, 7, 33, 2, 2, 143)         DT4261;-1.00000000E-04

(2024, 5, 22, 7, 33, 2, 2, 143)         45 [bpm]

(2024, 5, 22, 7, 33, 3, 2, 143)         DT4261;-1.00000000E-04

(2024, 5, 22, 7, 33, 3, 2, 143)         45 [bpm]

(2024, 5, 22, 7, 33, 3, 2, 143)         DT4261;-1.00000000E-04

(2024, 5, 22, 7, 33, 4, 2, 143)         DT4261;-1.00000000E-04

main_hr closed                                                   # Stop the loop.

(2024, 5, 22, 7, 33, 4, 2, 143)         DT4261;-1.00000000E-04

main_4261 closed

End.



```



## How can we handle successive notified packets as a client using aioble?

(A link to discussion of this topic can be found 

[here](https://github.com/orgs/micropython/discussions/15544).)



In the current version of ```aioble/client.py```, a data of a notified 

packet can be overwritten by those of the successive notified packets in 

the queue to which the data are appended.  This is because the size of the 

queue by default is 1:  ```self._notify_queue = deque((), 1)```



So *a ```while True:``` loop* with *a ```charateristic.notified()```* 

shown in the official examples, as well as ```hr_read.py``` shown above, are not 

necessarily useful; **notified packets should be well separated in time**.



Though I do not know exactly what is the future plan of the developers to 

solve the issue, there is a comment in ```aioble/client.py``` as follows:

```

# Append the data. By default this is a deque with max-length==1, so it

# replaces. But if capture is enabled then it will append.

```



As a workaround for Nordic UART client used in [mpy_xoss_sync.py](https://github.com/ekspla/xoss_sync), 

I changed the size of the queue and retrieved the accumulated notified data from the queue as followings.

``` python

buffer = bytearray()

async with connection:

    service = await connection.service(_SERVICE_UUID) # A Nordic UART Service.

    tx_characteristic = await service.characteristic(_TX_CHARACTERISTIC_UUID)

    rx_characteristic = await service.characteristic(_RX_CHARACTERISTIC_UUID)

    tx_characteristic._notify_queue = deque((), 7) # Change the size of the queue.

    await self.tx_characteristic.subscribe(notify=True)



    while True:

         await request_transport(rx_characteristic) # Send command to request transport.

         data = await tx_characteristic.notified()

         await asyncio.sleep(1) # Wait until the queue is filled.

         buffer.extend(data)

         while len(queue := tx_characteristic._notify_queue) >= 1:

             buffer.extend(queue.popleft())

         tx_characteristic._notify_event.clear() # Make sure to clear the flag.



         # Do something with the buffer.

```



The workaround is useful in this case because the server (peripheral) always waits for the response of the 

chunk of data from the client (micropython/aioble) before going to the next, and this waiting time can be used 

by the client to process (e.g. concatinate) the data in the queue.



A pair of test codes, ```nus_modem_client.py``` and ```nus_modem_server.py```, were prepared as the complete 

set of working example.  In this case, a primitive YMODEM file transfer protocol was implemented on 

[Nordic UART service's](https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/libraries/bluetooth_services/services/nus.html) 

TX/RX channels.  Athough there are limitations as described below, it works well as expected and has been 

already applied to [one of my projects](https://github.com/ekspla/xoss_sync).



The throughput measured was 27.7 kbps using 7.5 ms connection interval and tick rate of 1 ms (CONFIG_FREERTOS_HZ=1000) 

with ESP32-S3-WROOM-1-N16R8 and micro-SD card, while the theoretical limit assuming 3 connection events/128-byte data block 

is 45.5 kbps.



The limitations are due mainly to the implementation of YMODEM in part as follows:

- The script expects a transport with MTU of 23, 128-byte data per block, and CRC16/ARC (not CRC16/XMODEM).

Larger MTU by DLE (Data Length Extension) and 1024-byte data in YMODEM (STX), that make throughput higher, are not 

supported (not implemented yet).



## ESP32 chip as a USB bluetooth dongle (HCI H4) for use with unix-port (Linux) of micropython and aioble



A cheap USB bluetooth dongle was easily built by using an ESP32, a USB-UART chip ([CH340E](https://www.wch.cn/search?t=all&q=CH340E)) 

and a 600-mA LDO ([RT9080](https://www.richtek.com/Products/Linear%20Regulator/Single%20Output%20Linear%20Regulator/RT9080?sc_lang=en)). 

As shown in the figures below, I tried to reduce the lengths of the cables as short as possible to obtain the 

highest reliable speed.  USB-UART/LDO built on frontside and ESP32 mounted on backside were sticked together to form the 

home-made USB dongle. 

![PHOTO_FRONTSIDE_CH340_LDO](https://github.com/ekspla/micropython_aioble_examples/blob/main/figs/Frontside_CH340_LDO.jpg "Frontside")

![PHOTO_BACKSIDE_ESP32](https://github.com/ekspla/micropython_aioble_examples/blob/main/figs/Backside_ESP32.jpg "Backside")



The firmware on the ESP32, which was written through the pin sockets shown in the photo above, was built on `controller_hci_uart_esp32`, 

[an example of Espressif's ESP-IDF](https://github.com/espressif/esp-idf/tree/master/examples/bluetooth/hci), with the following parameters.



UART baudrate = 1 Mbps; 

hardware flow control; 

FreeRTOS tick rate = 1 ms; 

CPU frequency = 240 MHz; 

GPIO pins 5, 18, 23, 19 are used as TxD, RxD, CTS, RTS, respectively.



I had to modify the codes as followings to set the parameters as above.



Modify `ESP-IDF/components/bt/controller/esp32/Kconfig.in`:

``` Diff

    config BTDM_CTRL_HCI_UART_BAUDRATE

        int "UART Baudrate for HCI"

        depends on BTDM_CTRL_HCI_MODE_UART_H4

-       range 115200 921600

-       default 921600

+       range 115200 3000000

+       default 1000000

        help

```

Modify `sdkconfig.defaults`:

```

CONFIG_BT_BLUEDROID_ENABLED=n

CONFIG_BT_CONTROLLER_ONLY=y

CONFIG_BTDM_CTRL_HCI_MODE_UART_H4=y

CONFIG_BTDM_CTRL_HCI_UART_NO=1

CONFIG_BTDM_CTRL_HCI_UART_BAUDRATE=1000000

CONFIG_BTDM_CTRL_MODEM_SLEEP=n



# Other config

CONFIG_ESP_DEFAULT_CPU_FREQ_MHZ_240=y

CONFIG_ESP_DEFAULT_CPU_FREQ_MHZ=240

CONFIG_FREERTOS_HZ=1000

```

Run `idf.py menuconfig`, then `idf.py build`.



To use the other baudrate, you have to modify it also in `MPY/ports/unix/mpbthciport.c`, which defaults to 1 Mbps. 

Because I could not obtain reliable connections at 1.5, 2 and 3 M bps, the baudrate was set to 1 Mbps in my case.



[The MPY on Linux machine using NimBLE stack was built](https://github.com/orgs/micropython/discussions/10234) as 

follows: 

``` Shell

make -C ports/unix MICROPY_PY_BLUETOOTH=1 MICROPY_BLUETOOTH_NIMBLE=1

```



Because the built-in USB-UART kernel module did not work reliably at a very high speed, I had to compile the module 

using the latest source code (V1.8 on 2024.08) of the manufacturer obtained from [their website](http://www.wch.cn/download/CH341SER_LINUX_ZIP.html) 

or from [their github repository](https://github.com/WCHSoftGroup/ch341ser_linux). 

Before start using it, set an appropriate permission of the USB-UART device you are using (e.g. `chomod 666` or `adduser` 

to the `dialout` group).



You have to specify the USB-UART device if it is not `/dev/ttyUSB0` as written in `ports/unix/mpbthciport.c`.



In my case:

``` Python

MICROPYBTUART=/dev/ttyCH341USB0 micropython

MicroPython v1.23.0 on 2024-11-18; linux [GCC 11.5.0] version

Use Ctrl-D to exit, Ctrl-E for paste mode

>>> from bluetooth import BLE

>>> BLE().active(1)

True

>>> import aioble

>>> 

```



This dongle/unix-port MPY combination was successfully used with my aioble test code, 

[nus_modem_client.py](https://github.com/ekspla/micropython_aioble_examples/blob/main/nus_modem_client.py), 

in this repository.



- Additional notes: 

You can also use this USB dongle from the other softwares than MPY/aioble such as [BlueZ](https://github.com/bluez/bluez) and 

[Google Bumble](https://github.com/google/bumble) because the APIs of HCI H4 are common.