結果:

I have developed an acoustic sensor that can pick up water leaks at a substantial separation distance. The leaks must originate from pressurized plumbing, which causes the emission of broadband acoustics. The sensor is on a small PCB that communicates with the host controller via I2C. I have connected to an ESP8266 WiFi module and uploaded data to ThingSpeak. The entire project is open-source; you can view the documentation, design files, and firmware on github:

https://github.com/microphonon/acoustic-leak-detector

Let me know if you have any questions. Mike

Hi, I am a newcomer to ThingSpeak, and have created a channel for my soil-moisture sensor. I have checked "show status" of my channel. 'Channel Status Updates' widget appears, but no data are displayed. It is not responding. The widget is always blank despite new sensor data every hour. I would like to display default status messages. Why doesn't it work and what should I do ? I have searched all documentation but find no help there. br SpacerLabs Team

I am trying to extract the value of a couple of variables from a very basic web page. Although I can see the variable's values changing when I Inspect the page in Chrome Browser and Xcopy, I only get the variable name, not its value, when I select the option to "send your ThingHTTP request and view the response using the following URL:" Can anybody point this rookie in the right direction please?

Hi all, I currently have a forecasting of a variable based on the data that I collected. But is there a way to calculate what is the accuracy for the forecast? Thanks.

Hi everyone. I updated my IoT Debugger project on GitHub. You can use the debugger to view channel data from ThingSpeak.

Please Reply soon, its argent...

.

MATLAB R2022a provides app developers more control over user navigation through app components using the keyboard's Tab key.

Part 1. The new focus function: programmatically set keyboard focus to a UI component

Part 2. Modify focus order of components

Today we'll review Part 2. See yesterday's Community Highlight for Part 1.

-------------------------------------------------------------------------------------------------

Well-designed apps have an obvious flow through interactive fields and, as we learned yesterday, using the Tab key to move the focus to the next UI component is faster and more efficient than using a mouse. Here we'll learn how to read and set the tab order of UI components in an app.

Understanding tab and stacking order

By default, tab order in MATLAB apps is controlled by the stacking order in the Component Browser. Initially, the stacking order within the component browswer is based on the sequence in which the objects were added to the container object within the app. MATLAB R2020b gave us control to edit the stacking order by selecting a component and using either the Reorder tool from the Canvas toolstrip or by right-clicking the component and selecting Reorder from the context menu [1]. Tab order flows from bottom to top through the Component Browswer hierarchy for objects that are focusable. Sending a component backward within the stack sets its tab order to earlier relative to other components.

Setting tab focus order in R2022a

Three additional tab order features were added in MATLAB R2022a that make it easier to control app navigation with the Tab key.

1. Sort and Filter by Tab Order : Instead of using the Reorder tool which lists components in reverse tab-order and includes components that are not focusable, filter the list by focusable components and sort them by tab-order using the View dropdown menu within the Component Browser (label 1 in image below). From here, you can drag and drop components to set their tab (and stacking) order.

2. Auto Tab Order : To automatically sort focusable components within your app so that the tab order is from left-to-right and then top-to-bottom, in App Designer, from Design View, select the Canvas tab > Tab Order button > Apply Auto Tab Order (label 2 in image below). Alternatively, you can apply auto tab order to components within a container such as a uipanel or uitab by right-clicking on the container within the Component Browser and selecting Apply Auto Tab Order.

3. Visualize Tab Order : You no longer have to read and interpret the handle names in the component browser to understand the current tab order of UI components. Instead, view an animation of tab order within App Designer. From Design View, select the Canvas tab > Tab Order button > Visualize Tab Order (label 3 in image below).

.

Contextual focus control: the power of combining focus() with setting tab order

Yesterday's Community Highlight showed how to programmatically set UI component focus using the focus(c) function. This, combined with control of tab order, allows app developers to implement contextual focus control. For example, when a radio button is selected in the GIF below, the corresponding UI Tab is selected programmatically and the keyboard focus is set to the first component within the UI Tab thus allowing the user to smoothly continue keyboard navigation. This is achieved by a callback function that responds to changes in the Button Group that sets the SelectedTab property of the TabGroup and uses the new focus() function. For details, see the attached focusAndTabOrderDemo.mlapp.

-------------------------------------------------------------------------------------------------

Stay tuned

Follow Community Highlights to get notifications for new content.

Let us know what interests you in the new MATLAB R2022a release in the comment section below.

See also

• MATLAB documentation: Modify Tab Focus Order of Components
• Release notes: Modify tab focus order
• R2021a Highlight: keyboard shortcuts for UI Components
• Download the latest release of MATLAB

Footnotes

[1] R202b release notes: change the stacking order of UI components

This Community Highlight is attached as a live script.

.

MATLAB R2022a provides app developers more control over user navigation through app components using the keyboard's Tab key.

Part 1. The new focus function: programmatically set keyboard focus to a UI component

Part 2. Modify focus order of components

Today we'll review Part 1. Come back tomorrow for Part 2.

-------------------------------------------------------------------------------------------------

Programmatically set UI component focus

Did you know that you can save ~2 seconds every time you use a keyboard shortcut rather than reaching for your mouse [1,2]?

I need you to focus here: starting in MATLAB R2022a, use the new focus function to set keyboard focus to a specific UI component.

By specifying the component handle ( c ) in focus(c),

1. The figure containing the component is displayed
2. A blue frame appears around the component
3. The user can directly interact with the component.

.

Which components are focusable?

Focusable components are those that a user can interact with using the keyboard. So an object set to Enable='off' or Visible='off' cannot be in focus. See the documentation for more details.

What will you do with all of that extra time saved?

-------------------------------------------------------------------------------------------------

Stay tuned

Tomorrow we'll learn how to apply the new focus function with control of tab order to create contextual flow of UI component focus. Follow Community Highlights to get notifications.

Let us know what interests you in the new MATLAB R2022a release in the comment section below.

See also

• Release notes: focus
• R2021a Highlight: keyboard shortcuts for UI Components
• Download the latest release of MATLAB

Footnotes

[1] Lane et. al. (2005). International Journal of Human-Computer Interaction, 18(2).

[2] Michels (2018). median.com

This Community Highlight is attached as a live script.

Currently i am using lora from my end node to my dragino gateway and from my gateway, i push the sensor data up to thingspeak. i want to check that when my temperature graph hits above 30 it will send down a 1 or a command to my gateway and my gateway will transmit it to my end node to take action. i research and saw that react is one of the solution for on top but i do not know which action and how to use that specific action for this scenario.

Hi all, don't upload data to Thingspeak (sorry my english) I'm build this counter geiger https://www.electronics-lab.com/project/new-improved-geiger-counter-now-wifi/ but not upload data, only appear this to my channel:

29T23:17:58Z","entry_id":112,"field1":null},{"created_at":"2022-03-29T23:22:58Z","entry_id":113,"field1":null},{"created_at":"2022-03-29T23:27:58Z","entry_id":114,"field1":null},{"created_at":"2022-03-29T23:32:58Z","entry_id":115,"field1":null},{"created_at":"2022-03-30T18:43:09Z","entry_id":116,"field1":null},{"created_at":"2022-03-30T19:00:19Z","entry_id":117,"field1":null},{"created_at":"2022-03-30T19:05:19Z","entry_id":118,"field1":null},{"created_at":"2022-03-30T19:10:19Z","entry_id":119,"field1":null}]}

The code I'm use is there https://www.electronics-lab.com/project/new-improved-geiger-counter-now-wifi/ sorry it does not allow me to upload it because it is long

Assignments, quizzes, midterms, finals, grades, joys of success, the anxiety of low grades. Sounds like a typical cycle that students go through, right? Sometimes, all that hustle and bustle makes students forget that coding could be fun! Dr. Amin Rahman teaches AMATH 301 at the University of Washington. Many engineering students take this course and learn MATLAB in the course. He was looking for ways to keep students engaged and remind them that coding is fun. To achieve this goal Dr. Rahman and I set up a small competition in MATLAB Grader. Dr. Rahman selected several problems from MATLAB Grader problem collections. Students competed in this optional competition without the pressure of grades. They submitted their solutions; their submissions were automatically graded using MATLAB Grader and they got instant feedback. Green checkmarks for the correct answers empowered students and gamified coding. With the feedback they got, they continuously improved their code.

Prizes? Aside from the joys of coding in MATLAB, students won MathWorks-branded items like t-shirts, hats, and bags and proudly wore them as you can see in Dr. Rahman’s tweet.

Interested in using MATLAB Grader? Interested in accessing MATLAB Grader problem collections? Like to brainstorm ideas to make coding more fun? Reach out to us! We are here to help. Any creative ideas to make courses more engaging? Please share your ideas with this community!

I have a google gauge that shows my PM2.5 sensor values but I would like to make 3 gauges appear side by side that show the value of different sensors. How can I do that? Thanks

Hello everyone, I am new to ThingSpeak and ESP32, I would like to send IMU sensor acceleration data from my ESP32 to ThingSpeak so that I can use this data for further analysis. I have tried the example code provided in this link: Bulk-Update and this works perfectly fine for me with the default update interval and post interval. I also attached the code here.

#include <Wire.h>
#include <Arduino.h>
#include <Adafruit_MCP4725.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BNO055.h>
#include <utility/imumaths.h>
#include <WiFi.h>
#include "ThingSpeak.h"

// Define multiplexer address
#define TCAADDR 0x70

// Define imu and dac objects
Adafruit_BNO055 bno = Adafruit_BNO055(55, 0x28);

char jsonBuffer[500] = "[";

char ssid[] = "my ssid";
char pass[] = "my password";
WiFiClient client;

char server[] = "api.thingspeak.com";

unsigned long lastConnectionTime = 0;
unsigned long lastUpdateTime = 0;
const unsigned long postingInterval = 15L * 1000L;
const unsigned long updateInterval = 3L * 100L;

// To choose the multiplexer specific channel (between 0 and 7)
void tcaselect(uint8_t i){
  if (i > 7) return;

Wire.beginTransmission(TCAADDR);
Wire.write(1 << i);
Wire.endTransmission();
}

    void setup() {
      // put your setup code here, to run once:
  Wire.begin();
  Serial.begin(9600);
  while(!Serial);
  delay(1000);
  Serial.println("Serial communication set up");

// set up bno055
tcaselect(2);
if (!bno.begin()){
  Serial.println("Failed to connect to BNO055");
  while (1);
}

while(WiFi.status() != WL_CONNECTED){
  Serial.print("Attempting to connect to wifi");
  WiFi.begin(ssid, pass);
  delay(5000);
}
Serial.println("Connected to WiFi");
printWiFiStatus();
}

void loop() {
  // put your main code here, to run repeatedly.

if (millis() - lastUpdateTime >= updateInterval){
  updatesJson(jsonBuffer);
}
}

void updatesJson(char* jsonBuffer){
  /* JSON format for updates paramter in the API
   *  This examples uses the relative timestamp as it uses the "delta_t". You can 
also provide the absolute timestamp using the "created_at" parameter
 *  instead of "delta_t".
 *   "[{\"delta_t\":0,\"field1\":-70},{\"delta_t\":3,\"field1\":-66}]"
 */
// Format the jsonBuffer as noted above
strcat(jsonBuffer,"{\"delta_t\":");
unsigned long deltaT = (millis() - lastUpdateTime)/1000;
size_t lengthT = String(deltaT).length();
char temp[4];
String(deltaT).toCharArray(temp,lengthT+1);
strcat(jsonBuffer,temp);
strcat(jsonBuffer,",");

tcaselect(2);
sensors_event_t orientationData , angVelocityData , linearAccelData, magnetometerData, accelerometerData, gravityData;

bno.getEvent(&orientationData, Adafruit_BNO055::VECTOR_EULER);
bno.getEvent(&angVelocityData, Adafruit_BNO055::VECTOR_GYROSCOPE);
bno.getEvent(&linearAccelData, Adafruit_BNO055::VECTOR_LINEARACCEL);

float rssi = linearAccelData.acceleration.x; 
strcat(jsonBuffer, "\"field1\":");
lengthT = String(rssi).length();
String(rssi).toCharArray(temp,lengthT+1);
strcat(jsonBuffer,temp);
strcat(jsonBuffer,"},");
// If posting interval time has reached 15s, update the ThingSpeak channel with your 
data
if (millis() - lastConnectionTime >=  postingInterval) {
      size_t len = strlen(jsonBuffer);
      jsonBuffer[len-1] = ']';
      httpRequest(jsonBuffer);
}
lastUpdateTime = millis(); // Update the last update time
}

// Updates the ThingSpeakchannel with data
void httpRequest(char* jsonBuffer) {
/* JSON format for data buffer in the API
 *  This examples uses the relative timestamp as it uses the "delta_t". You can also 
provide the absolute timestamp using the "created_at" parameter
 *  instead of "delta_t".
 *   "{\"write_api_key\":\"YOUR-CHANNEL-WRITEAPIKEY\",\"updates\": 
[{\"delta_t\":0,\"field1\":-60},{\"delta_t\":15,\"field1\":200}, 
{\"delta_t\":15,\"field1\":-66}]
 */
// Format the data buffer as noted above
char data[500] = "{\"write_api_key\":\"59IISQVOXV5GGH0D\",\"updates\":"; // Replace 
YOUR-CHANNEL-WRITEAPIKEY with your ThingSpeak channel write API key
strcat(data,jsonBuffer);
strcat(data,"}");
// Close any connection before sending a new request
client.stop();
String data_length = String(strlen(data)+1); //Compute the data buffer length
Serial.println(data);
// POST data to ThingSpeak
if (client.connect(server, 80)) {
  client.println("POST /channels/1683708/bulk_update.json HTTP/1.1"); // Replace 
YOUR-CHANNEL-ID with your ThingSpeak channel ID
  client.println("Host: api.thingspeak.com");
  client.println("User-Agent: mw.doc.bulk-update (Arduino ESP8266)");
  client.println("Connection: close");
  client.println("Content-Type: application/json");
  client.println("Content-Length: "+data_length);
  client.println();
  client.println(data);
}
else {
  Serial.println("Failure: Failed to connect to ThingSpeak");
}
delay(250); //Wait to receive the response
client.parseFloat();
String resp = String(client.parseInt());
Serial.println("Response code:"+resp); // Print the response code. 202 indicates that 
the server has accepted the response
jsonBuffer[0] = '['; //Reinitialize the jsonBuffer for next batch of data
jsonBuffer[1] = '\0';
lastConnectionTime = millis(); //Update the last conenction time
}

void printWiFiStatus() {
  // Print the SSID of the network you're attached to:
  Serial.print("SSID: ");
  Serial.println(WiFi.SSID());

// Print your device IP address:
IPAddress ip = WiFi.localIP();
Serial.print("IP Address: ");
Serial.println(ip);

// Print the received signal strength:
long rssi = WiFi.RSSI();
Serial.print("signal strength (RSSI):");
Serial.print(rssi);
Serial.println(" dBm");
}

However, when I tried to change the update interval to 0.3s (30Hz), the following error massage was given in the Arduino monitor: Guru Meditation Error: Core 1 panic'ed (LoadProhibited). Exception was unhandled.

Could someone please help me with this issue. If anything else is needed, I will update immediately.

Many thanks

I saw this problem online recently.

Passenger distribution on a train

Not a terribly difficult problem to solve. But it was mildly interesting to find a solution using MATLAB. Perhaps just as interesting is the post analysis of the problem to understand what is happening, and why any unique solution exists at all for one specific car.

The question is, we have a passenger train with 11 cars in it. Feel free to number them 1 through 11. We know that 381 passengers boarded the train. Every passenger is in one of the cars, but all we know is there are exactly 99 passengers in every set of three consecutive cars. Now the question becomes, how many passengers are in car number 9?

One might say at first this is impossible to know. Surely there are many ways the passengers may be arranged, but is that true? Could it be impossible to solve?

First, before we go any further, a few tests seem important. Logically, we might think to distribute 33 passengers in every car. Would that work? So we would have a passenger distribution of

X1 = repmat(33,11,1)

X1 =
    33
    33
    33
    33
    33
    33
    33
    33
    33
    33
    33

While that satisfies the requirement of every 3 consecutive cars having 99 passengers, it fails the total count requirement, since we can see the sum of all passengers would be 363. This yields too few total passengers, with only a combined load of 363 passengers, and we need 381.

At the other end of the spectrum is another extreme case. We might have this distribution:

X2 = zeros(11,1);
X2(1:3:11) = 99
X2 =
    99
     0
     0
    99
     0
     0
    99
     0
     0
    99
     0

Again, it meets the requirement that the sum of passengers in any 3 consecutiuve cars will be 99. But that case yields too many total passengers at 396. Somewhere in the middle must/might/may be a solution, right? At least it is good to see that we can have more or less than 381 total passengers. But how can we find a solution using MATLAB?

There is one other problem with the X2 attempt at a solution, in that had I chosen a different first car to place the 99 passengers, we need not have a unique result in car number 9.

X3 = zeros(11,1);
X3(2:3:11) = 99;

X4 = zeros(11,1);
X4(3:3:11) = 99;

Each of those schemes would put 99 passengers in every set of 3 consecutive cars.

[X2,X3,X4]
ans =
    99     0     0
     0    99     0
     0     0    99
    99     0     0
     0    99     0
     0     0    99
    99     0     0
     0    99     0
     0     0    99
    99     0     0
     0    99     0

But car number 9 would have very different numbers of passengers, depending on the choice made, either 0 or 99 passengers.

An obvious solution is to look for a code that can solve such a problem for us. INTLINPROG stands out as the perfect tool, as this is a linear problem, with everything being in the form of a sum. The unknowns will be how many passengers are sitting in each car. There are 11 cars. So there are 11 unknowns. The bounds are simple.

lb = zeros(1,11); % There cannot be less than zero passengers in any car.
ub = repmat(99,1,11); % since the sum of any three consecutive cars is 99, we cannot have more than 99 people in any one car.

All of the unknown car counts must be integer. That is, we cannot have a fractional number of people in a car, unless this is part of an Agatha Christie murder mystery.

intcon = 1:11;

What constraints apply? First, the sum of all passengers on the train must be 381.

As well, we know that in every 3 consecutive cars, the sum must be 99. Both constraints will take the form of exact linear equality constraints. We can encode all of that into the matrix Aeq, and the vector Beq.

Aeq = [ones(1,11);triu(tril(ones(9,11),2))]; % A tricky way to create the matrix Aeq
Beq = [381;repmat(99,9,1)];

If X is a potential solution that satisfies the bound constraints, it must satisfy the matrix equation Aeq*X==Beq.

We can see for example, the potential solutions I posed above as X1,...X4, all fail to satisfy the requirement on the total number of passengers, since while the sums for consecutive cars are correct, the total sum is not.

Aeq*[X1,X2,X3,X4]
ans =
   363   396   396   297
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99
    99    99    99    99

Finally, there are no linear inequality constraints.

A = [];
B = [];

At this point, you might be wondering how we can formulate this as a linear programming problem at all. What would be the objective function? What could we hope to minimize? As it turns out, linear programming tools are pretty simple in that respect. We could pose just about any objective we want. For example, this is sufficient:

f = ones(1,11);

Effectively, we are just using intlinprog to see if a FEASIBLE integer solution exists that satisfies all of the bounds, as well as the equality constraints. This is why the objective can be the same as one of the equality constraints. Once INTLINPROG finds any solution, it will be done.

And now we can throw the problem into INTLINPROG, hoping something intelligent falls out.

[X,~,EXITFLAG] = intlinprog(f,intcon,A,B,Aeq,Beq,lb,ub)
P:                Optimal objective value is 381.000000.                                           

Optimal solution found.

Intlinprog stopped at the root node because the objective value is within a gap tolerance of the optimal value,
options.AbsoluteGapTolerance = 0 (the default value). The intcon variables are integer within tolerance,
options.IntegerTolerance = 1e-05 (the default value).

X =
     0
    84
    15
     0
    84
    15
     0
    84
    15
     0
    84
EXITFLAG =
     1

intlinprog has found a solution,

isequal(Aeq*X,Beq)
ans =
  logical
   1

The solution satisfies all of the constraints. Effectively, we see the repeating sub-sequence [0 84 15] in consecutive cars. And of course, as long as we repeat that sequence, it does satisfy all requirements. How many people are sitting in car number 9? 15 people.

Symmetry would suggest that car number 3 must have the same number of people, since we could as easily have numbered the cars starting from either end. And of course, X(3) was also 15.

Thankfully our intuition works there. It would seem we are done now. Or are we?

For some of you, you might be wondering if any other solutions can possibly exist. And some of you might be wondering if any of those solutions can have some other number of passengers than exactly 15 in cars number 3 and 9.

NULL is the MATLAB function to come to the rescue here.

This is essentially a linear algebra question. We wish to know the solutions of the problem Aeq*x==Beq. Here, Aeq is a 10x11 matrix, so it has rank at most 10. That means there is a vector Y, such that Aeq*Y == 0.

Y = double(null(sym(Aeq)))
Y =
    -1
     1
     0
    -1
     1
     0
    -1
     1
     0
    -1
     1

What does that tell us? If we have some particular solution (X) to the non-homogeneous problem Aeq*X==Beq, then the set of all possible solutions will be of the general form

syms t
X + t*Y
ans =
    -t
t + 84
    15
    -t
t + 84
    15
    -t
t + 84
    15
    -t
t + 84

You may see that this generates all solutions to the general problem. We can see a few of them in this array:

[X-1*Y, X - 2*Y, X - 3*Y, X - 84*Y]
ans =
     1     2     3    84
    83    82    81     0
    15    15    15    15
     1     2     3    84
    83    82    81     0
    15    15    15    15
     1     2     3    84
    83    82    81     0
    15    15    15    15
     1     2     3    84
    83    82    81     0

We see now there are 85 such possible integer solutions, all of the form X-k*Y, where k can be any positive integer from 0 to 84 inclusive. INTLINPROG found one of them. But as importantly, do you see that since the elements

Y([3 6 9])
ans =
     0
     0
     0

are all identically zero, that those elements in the solution can never change? Those cars must always contain exactly 15 passengers for all of the constraints to be satisfied. I'll be honest, it is not at all obvious as to why it works out that way, at least not initially in my eyes. That leaves my intuition wanting, just a bit.

How might we analyze this problem in a different way? Perhaps a different approach would yield a more satisfying solution. Suppose we chose a passenger partitioning that is strictly repetitive? For example, choose three non-negative integers u,v,w, such that u+v+w=99.

Now, fill the cars using the sequence

syms u v w
X = [u v w u v w u v w u v];

Surely you would agree that any subset of 3 consecutive cars adds to 99, as long as u+v+w=99. But then the sum of all 11 cars in that sequence must be 4*u+4v+3*w. And this leaves us with now two equations in three unknowns. We have

EQ1 = sum(X) == 381;
EQ2 = u + v + w == 99;

The rest is easy now, as we can do

EQ1 - 3*EQ2
ans =
u + v == 84

So if a solution in this form exists, we can see that u+v=84, and therefore w=99-u-v=15. (Remember that w was the number of passengers in car number 9, but also in cars numbered 3 and 6.) Any combination of non-negative integers that sums to 84 will work for u and v though.

This constructive approach does not insure it is the ONLY solution, since I built it from the sequence in the vector X. Perhaps a solution exists that is not simply repetitive as I created it. In fact, the previous analysis using null told us the whole story.

Starting in MATLAB R2022a, use the append option in exportgraphics to create GIF files from animated axes, figures, or other visualizations.

This basic template contains just two steps:

% 1. Create the initial image file
gifFile = 'myAnimation.gif';
exportgraphics(obj, gifFile);

% 2. Within a loop, append the gif image
for i = 1:20

      %   %   %   %   %   %    % 
      % Update the figure/axes %
      %   %   %   %   %   %    % 

      exportgraphics(obj, gifFile, Append=true);
  end

Note, exportgraphics will not capture UI components such as buttons and knobs and requires constant axis limits.

To create animations of images or more elaborate graphics, learn how to use imwrite to create animated GIFs .

Share your MATLAB animated GIFs in the comments below!

See Also

• Animation Techniques
• Animating plots

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