Two way communication using Python (bleak) / Cannot discover services & characteristics

Posted on Wed 5th, May 2021

• #1

boomNinjaVanish

tl;dr version: how do I push changes to a central device (Raspberry Pi)? Libraries I have tried do not discover UART service and characteristics.

Hi!

I am working on a project to help my disabled sister to operate devices in her house on her own. I am planning on using a combination of the Puck's accelerometer and a Raspberry Pi running this project: https://webgazer.cs.brown.edu/#examples. I hope to publish this as open source so that others may use the project for their needs as well. (Products in the medical industry are VERY expensive. I am hoping that making some things available for free would help those who cannot afford an expensive solution from Tobii/Dynavox.)

She cannot speak, walk, or move very well. However, she can make her Barbie dance by shaking it. I am hoping to harness that movement as an trigger for various home automation tasks in the future. My end-goal is to have her control everything in her environment. She would do this by gazing at the Raspberry Pi's screen to change which device/setting and shake the Puck to change the state of that device. She lives in an impoverished area without access to the internet, so I am looking to make a closed network of IoT devices for her.

Right now, I am starting small: I am making the Puck act as a thermostat and controller for a fan in my kitchen using http get requests to IFTTT.

After multiple hours of experimentation, I was able to get the Puck to receive commands from my macos device. However, I am having trouble figuring out how to have the server wait for a command from the the Puck. Is there a way to have the puck push data to the server? For example, if the puck has been flipped (accel.z < 0), I want to send an instruction to the server to shut off the fan. I also want to do this using as little power as possible.

One last thing: I was able to get the bleak library to work on both macos and Ubuntu on the Raspberry Pi. However, when I attempt to discover services and characteristics, the Puck doesn't respond. I have tried multiple libraries in both node js and python to no avail. (I would love to use @abandonware/noble in node but I could not get that to discover the UART characteristics as well. ) EDIT: To be clear: it does TX and RX to and from the server but discovery doesn't work.

Thanks for reading all of this. Here a link to the GitHub for the thermostat. I will make the eye gaze/motion project open source and available when I start it as well.
• #2

Gordon
Hi! This sounds like a great project!

With Bleak, did you try the code on https://www.espruino.com/Interfacing#bluetooth-le ? What error messages do you get?

Actually trying to directly make HTTP requests from the Puck via some means is going to be difficult, but I feel like you've got a few different options:
- Use the EspruinoHub project on the Raspberry Pi, which will bridge Bluetooth to MQTT. You can even plug it into 'Home Assistant': https://github.com/espruino/EspruinoHub#home-assistant-integration
- Use the code from https://www.espruino.com/BLE+Advertising so you're using Bluetooth Advertising from the Puck. This isn't quite as flexible (it's not two-way to the Puck) but it is super robust and easy (it's what the EspruinoHub stuff used by default too).
- Make the Puck a Bluetooth HID keyboard (https://www.espruino.com/BLE+Keyboard) - you can then just pair it with the PC/Raspberry Pi and make it 'fake' different keypresses to do what you want. I've seen Pucks used this way for accessibility a few times.

• #3

Here is the output I receive when I run the example code on my mac. It hangs at the second "connected":

± % node test.js                                                                                                  !6614
Noble: stateChange -> poweredOn
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  be-89-30-00-21-95
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  90-dd-5d-e8-59-50
Found device:  90-dd-5d-e8-59-50
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  
Found device:  f2-09-f2-78-7d-9a
BT> Connecting
Found device:  f2-09-f2-78-7d-9a
BT> Connecting
BT> Connected
BT> Connected
^C

EDIT: Changed the wording below to be less confusing.

I am not making direct HTTP requests from the Puck but from a raspberry pi. How does one press a button on the device to trigger the HTTP request on the raspberry pi? Then after that poll the puck for the temperature?

Sorry, I am new to BLE and have been confused by hours of reading about it.

• #4

boomNinjaVanish

Tried the example on the raspberry pi and got this output:

ubuntu@boontoo:~/motion-thermostat$ node test
Noble: stateChange -> poweredOn
Found device:  45:73:5f:0c:0d:10
Found device:  64:2b:d2:47:bd:00
Found device:  cc:f4:11:98:5b:01
Found device:  05:c9:79:4c:61:39
Found device:  12:7d:20:2d:64:3b
Found device:  0e:a1:1e:0e:0e:c2
Found device:  75:d9:c4:33:59:a8
Found device:  58:c6:8d:82:1f:a2
Found device:  06:42:db:89:b9:90
Found device:  2f:6a:ef:b1:6d:d2
Found device:  74:2f:a8:98:9c:57
Found device:  78:02:b7:23:6b:c2
Found device:  49:92:1d:5b:82:d6
Found device:  4b:ef:f5:a0:e9:2a
Found device:  6b:73:24:90:68:e4
Found device:  ea:c5:8b:e0:a4:fb
Found device:  68:ce:65:cb:86:28
Found device:  0e:a1:1e:0e:0e:c2
Found device:  0c:80:5f:d6:bd:0c
Found device:  0c:80:5f:d6:bd:0c
Found device:  05:c9:79:4c:61:39
Found device:  90:dd:5d:e8:59:50
Found device:  54:e4:fc:4c:f1:9b
Found device:  0e:a1:1e:0e:0e:c2
Found device:  45:73:5f:0c:0d:10
Found device:  64:2b:d2:47:bd:00
Found device:  3d:7f:60:53:b0:7d
Found device:  55:2b:6a:2d:44:29
Found device:  5f:a3:6c:c7:29:84
Found device:  12:7d:20:2d:64:3b
Found device:  75:d9:c4:33:59:a8
Found device:  58:c6:8d:82:1f:a2
Found device:  06:42:db:89:b9:90
Found device:  2f:6a:ef:b1:6d:d2
Found device:  74:2f:a8:98:9c:57
Found device:  0e:a1:1e:0e:0e:c2
Found device:  62:5e:f6:87:87:d9
Found device:  45:9a:95:02:55:00
Found device:  05:c9:79:4c:61:39
Found device:  90:dd:5d:e8:59:50
Found device:  54:e4:fc:4c:f1:9b
Found device:  48:10:c1:2a:74:cc
Found device:  48:10:c1:2a:74:cc
Found device:  f4:fe:fb:c4:58:4e
Found device:  4e:b6:b3:37:6d:f9
Found device:  4e:b6:b3:37:6d:f9
Found device:  40:2d:01:84:21:eb
Found device:  08:a1:94:e2:dd:f7
Found device:  0e:a1:1e:0e:0e:c2
Found device:  0c:80:5f:d6:bd:0c
Found device:  69:be:d5:4e:3a:dc
Found device:  6c:ef:9f:dd:1d:ae
Found device:  64:2b:d2:47:bd:00
Found device:  f4:fe:fb:c4:58:4e
Found device:  55:2b:6a:2d:44:29
Found device:  67:8c:04:e3:bf:13
Found device:  67:8c:04:e3:bf:13
Found device:  90:dd:5d:e8:59:50
Found device:  7c:18:2f:c5:ce:04
Found device:  12:7d:20:2d:64:3b
Found device:  5f:a3:6c:c7:29:84
Found device:  58:c6:8d:82:1f:a2
Found device:  5f:a3:6c:c7:29:84
Found device:  45:9a:95:02:55:00
Found device:  61:d5:e4:67:76:80
Found device:  61:d5:e4:67:76:80
Found device:  68:ce:65:cb:86:28
Found device:  08:a1:94:e2:dd:f7
Found device:  90:dd:5d:e8:59:50
Found device:  f2:09:f2:78:7d:9a
BT> Connecting
Found device:  f2:09:f2:78:7d:9a
BT> Connecting
BT> Connected
BT> Connected
Disconnected
Disconnected
Disconnected
Disconnected
^Cubuntu@boontoo:~/motion-thermostat$

• #5

Gordon

So you're running the code from this example? https://www.espruino.com/Interfacing#node-js-javascript

It seems that maybe it's trying to connect to the device twice, so you could try changing the code right at the top to:

var foundDevice = false;
noble.on('discover', function(dev) {
  if (foundDevice) return;
  console.log("Found device: ",dev.address);
  if (dev.address != ADDRESS) return;
  noble.stopScanning();
  foundDevice = true;
  connect(dev, function() {
    // Connected!
    write(COMMAND, function() {
      btDevice.disconnect();
    });
  });
});

Does the code make the Puck's light flash?

How does one press a button on the device to trigger the HTTP request on the raspberry pi? Then after that poll the puck for the temperature?

The best bet there is to use https://www.espruino.com/BLE+Advertising

So on the Puck:

var presses = 0;

function updateAdvertising() {
NRF.setAdvertising({},{manufacturer: 0x0590, manufacturerData:[presses,E.getTemperature()]});
}

setWatch(function() {                                                          
  presses++;                                                                   
  updateAdvertising();
}, BTN, {edge:"rising", repeat:1, debounce:20});
// update advertising with new temperature once a minute
setInterval(updateAdvertising, 60000); 
// update advertising right now
updateAdvertising();

And then use the code from https://www.espruino.com/BLE+Advertising#node-js - either JS or Python. The first byte you get will be the button press count - so when it changes you can do your HTTP request - and the second byte is the temperature, so there's no need to request it - you just always have it available.

• #6

boomNinjaVanish

Does the code make the Puck's light flash?

It flashed!

And then use the code from https://www.espruino.com/BLE+Advertising#node-js - either JS or Python. The first byte you get will be the button press count - so when it changes you can do your HTTP request - and the second byte is the temperature, so there's no need to request it - you just always have it available.

I will give this a try tomorrow. Thanks for the help!
• #7

Gordon

Great! Did you have to make the change I described above? If so I'll change the example code on the website
• #8

boomNinjaVanish in reply to @Gordon

Great! Did you have to make the change I described above? If so I'll change the example code on the website

Yup! That is what fixed it!

I got the project to work the way I was expecting: the device may be flipped to turn the fan on and off and is controlled by a temperature. I used node with @abandonware/noble for the server like I wished! Now I know enough to make the project for my sister. I am super stoked!

Thanks for the help! I now understand BLE two way communications!

BTW -- if you want to post it as a project, I have the completed thermostat code and instructions here:
https://github.com/boomninjavanish/motion-thermostat

I will improve upon this project over time as I really needed the thermostat. (I plan on adding two more features to it soon.)

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Two way communication using Python (bleak) / Cannot discover services & characteristics

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