Get specific number of BLE notifications

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Lars Urban
Lars Urban 2021-11-27
回答： Frodo Muijzer 2023-2-10
Ran in:
Hi,
I'm writing a script trying to get 10 notifications from a BLE device. The value contiains a char-array which i then want to display (and later save to csv, not implemented).
I want to get the values as soon as they are available and dont want double readings so I thought using the notification feature of BLE might work. I dont know how to use the DataAvailableFcn though. I get this error:
Error using BLETest (line 10)
Invalid value for DataAvailableFcn. Specify [] or a function handle that accepts two inputs.
The MATLAB exaples only use delays and read the data periodicly.
My code looks like this:
clear esp
esp = ble("BLE");
Scanning and connecting to Bluetooth Low Energy peripheral devices are not supported on Linux.
c = esp.characteristic("41BD8A4C-4E52-11EC-81D3-0242AC130003","17789A04-4E54-11EC-81D3-0242AC130003");
subscribe(c);
measurements = 10;
for m = 1:measurements
c.DataAvailableFcn = @displayData;
end
unsubscribe(c);
function displayData()
data = c.read();
text = char(data);
disp(text);
m + 1;
end

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回答（2 个）

Harikrishnan Balachandran Nair
Hi Lars,
The 'DataAvailableFcn' property should be assigned a Function Handle that accepts two inputs . In the code you have provided, the function 'displayData' does not have any input arguments, and hence the error occurs.
You can refer to the example here to get a better idea on this : https://www.mathworks.com/help/matlab/ref/matlabshared.blelib.characteristic.read.html#mw_5cba06cb-595e-44b8-82cd-44a397a29c74
Frodo Muijzer
Frodo Muijzer 2023-2-10
Hello,
It's an old topic, but I'm running into the almost same issue (And same error message). From the help/example listed above, I'm able to print the results of the notication to the output window, so the BLE communication works. But how do I get the data received from my device back to my main script, for example to plot it or write it to a file?
As soon as I try to add arguments to the function call, it complains that the function only acceps two inputs (presumably src and evt that are already present under water.) How do I add arguments to the function call?
accel_ble.DataAvailableFcn = {@read_accel_Data, x1, y1, z1};
function read_accel_Data(src, evt, x_plot, y_plot, z_plot)
....
end
doesn't work, also tried many variants with square brackets etc.
Thanks in advance for the hints!
accel_ble.DataAvailableFcn = @read_accel_Data;
...
function read_accel_Data(src, evt)
[accel_raw,timestamp] = read(src,'oldest') ;
for i = 1:1:3 % x,y,z
accel(i) = accel_raw(2*i-1); %MSB
accel(i) = bitor(accel(i), bitshift(accel_raw(2*i),8,'int16'),'int16'); %LSB
end
%this gives an error, since x_plot etc. are not known in this context.
addpoints(x_plot,timestamp,accel(1));
addpoints(y_plot,timestamp,accel(2));
addpoints(z_plot,timestamp,accel(3));
end

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