In the first article - How to connect a Particle device to Blynk, I demonstrated how to send a set of data values to Blynk, updating values displayed on a web dashboard and mobile app, and how to trigger user notifications on both. The Particle firmware function Particle.publish() was used to send data to a Particle integration webhook. The webhook transformed the data, and then pushed it to the Blynk cloud using the Blynk HTTPs API.
In this article, I will show you how to control a Particle device remotely from either the Blynk web dashboard (Blynk.Console), or the Blynk mobile app (Blynk.App).
We will begin at the destination of the Particle Boron IoT device, and then work our way back to the action triggered by the widget on either the Blynk dashboard or mobile app. An overview of the process consists of the following:
- Blynk will push data to the device through a Blynk widget connected to a Blynk webhook.
- The Blynk webhook sends a HTTP POST and interacts with the Particle cloud via its API.
- The Particle cloud sends a value to the Particle device via a Particle function configured on the device.
Why Use Blynk?
Particle doesn’t have long term data storage, web dashboard, or a mobile app for device remote control and data visualization. Particle does have powerful no-code webhooks / integrations that are used to connect a Particle device with a 3rd party data storage and web dashboard. Particle’s app is solely for claiming a device.
Connecting a Particle device to Blynk adds historical data storage, a no-code web dashboard, iOS / Android mobile apps, and automations. Blynk offers scalable tools for user and device management including multi-level organization structures and flexible permission controls.
Functional Specification
The functional requirements for this project are very simple.
- Change the state of a digital output on a Particle device built-in LED using either a pushbutton on the Blynk dashboard, or a Button’ widget in the Blynk.App.
Hardware
The Particle device is a Boron 404x cellular LTE Cat M1 device. The built-in LED on the device connected to digital I/O D7 will be utilized.
Firmware
A Particle cloud function causes code on a device to run when requested from the Particle cloud API. Up to 15 cloud functions may be registered, and each function call request and response uses one Particle Data Operation from your monthly or yearly quota. The function can also be triggered from the Particle console, and the CLI. The function returns an integer defined by the function code.
Below is the firmware code for the Boron. Note that the cloud function is first registered in setup() by the call to Particle.function(funcKey, funcName), and then the custom function ‘funcName’ is added to the script. In this example, the funcKey is ‘blynk_led’ and the funcName is ‘blynkLED’.
Upload the firmware code to the Boron and then continue to power it so it can connect to the Particle cloud. Go to your Particle console, select the Boron device, and then under the section ‘FUNCTIONS’ on the right side of the screen you will see the function key of ‘blynk_led’ listed. Enter ‘on’ in the ‘Argument’ input area and click the ‘CALL’ button. Observe the Boron to confirm that the built-in blue LED on D7 turns on. Repeat, this time with the ‘off’ argument to turn off the LED.
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Particle API
Now that we have confirmed that the Particle function works properly on the Boron, let's execute it using the Particle API. Create an access token by logging into your Particle account, and then visiting the Particle documentation section ‘Create a token (browser-based)’. Use your Particle login email and password. If you have MFA (multi-factor authentication) enabled on your account, you will need your MFA code to generate the access token. Click the ‘Create token’ button to generate a token. Keep this token confidential.
The syntax for the API is:
Where {DEVICE_ID} is your particle device ID and {FUNCTION} is the cloud function name.
Example:
Configure an HTTPs POST with OAuth 2.0 authorization, a webform with the key/values of “args” and “on” using a tool such as the free online tool Postman, as shown in the images that follow. First select ‘POST’, enter the URL, select the ‘Authorization’ tab and set the ‘Type’ to ‘OAuth 2.0’. Select the ‘Request Headers’ option and then enter your 40 character Particle access token into the token field, and then the text “Bearer” for the ‘Header Prefix”.
Configure the POST body message type as application/x-www-form-urlencoded with the following key/value pairs:
args on / off
The ‘args’ value should be “on” or “off”, depending on if you want to turn the built-in LED on or off.
For clarity, the full headers that will be sent with the HTTP POST by Postman are shown below. Note the key of ‘Authorization’ and the value of ‘Bearer {40 char Particle access token}’. A space is in between “Bearer” and the 40 character Particle access token. This is known as ‘Bearer Authorization’ or ‘token authentication’ and is an HTTP authentication scheme that involves security tokens called bearer tokens. In this case, the bearer token will be sent in an HTTP ‘Authorization’ header.
With your device powered and connected, manually send a POST using Postman or CURL with the ‘args’ value of either ‘on’ or ‘off’. If your response is unsuccessful, the response will be:
The above response occurs if your Particle device isn’t online (Status: 400 Bad Request)
A successful execution will appear as follows:
Note that if you add a body key of “format” and value of “raw” then the response will simply be the integer value you configured for your Particle function ‘blynkLED()’ with a value of -1, 1 or 0.
Now that you are certain that the Particle HTTP POST will be responded to by the Particle device, the next step is to configure a Blynk Webhook that will execute that POST. The Blynk webhook will pass a datastream value in the Particle HTTP POST, so begin by defining the Blynk datastream.
Blynk Datastreams
Blynk Datastreams are bi-directional channels assigned a data type and link to data values stored on the Blynk Cloud. You reference them as virtual pins between the range of V0 and V255. Below are the datastreams defined for this project and their relationship to the hardware and the web dashboard / mobile app.
The Particle function argument is a data type of String. The custom function we created accepts values of ‘on’ or ‘1’ to turn the built-in LED on, and values of ‘off’ or ‘0’ to turn it off. Note below that the enumerable datastream converts 1/0 to “on”/”off”.
Blynk Datastream Definitions
Blynk Device Template
If you already followed the steps from the prior article How to connect a Particle device to Blynk, then edit the same device template and add the datastreams V7, V8, V9 as shown below.
Using the Blynk Datastream Definitions listed in the table, create or edit a device template named ‘BRN404X’ as shown below.
Three datastreams of data types integer, enumerable, and string will be created to illustrate how each can be used to control the LED on the Particle Boron. In a real application, you would only need to employ one of these.
Click on the ‘Templates->Datastreams’ tab and configure the datastreams as defined in the Blynk Datastream Definitions table with the options as shown below. It is important to configure the Pin, Data Type, Is Raw, Min, Max, and Default Value as shown.
Blynk Web Dashboard
If you already followed the steps from the prior article How to connect a Particle device to Blynk, then add a new dashboard tab by clicking the ‘+’ button before following the steps below.
Create a web dashboard by navigating to ‘Templates->[template name = BRN404X]’ and then click on the ‘Web Dashboard’ tab. Create a dashboard as shown below, using a switch widget for virtual pins V7 and V8, and a text input widget for the string datastream V9. The label widgets to the right of each switch / text input widget are not required and are only to make it easy for you to see the latest datastream value.
Blynk Mobile App
If you already followed the steps from the prior article How to connect a Particle device to Blynk, then edit the same device template ‘boronc’ and add the three widgets for datastreams V7, V8, V9 as shown below.
Create a Blynk mobile device dashboard. The exact steps may vary between iOS and Android, but begin by tapping on a device, and tap on the wrench icon and then the ‘+’ icon to add a widget. Create the following widgets:
- ‘Switch’ widget for datastream ‘LED int (V7)’.
- ‘Segmented Switch’ widget for datastream ‘LED enum (V8)’.
- ‘Text Input’ widget for datastream ‘LED str (V9)’.
Blynk Device Activation
Skip this step if you already followed the steps from the prior article How to connect a Particle device to Blynk. If you didn’t, then go to that article and follow the steps under ‘Blynk Device Activation’.
Blynk Webhook
Navigate to ‘Settings -> Webhooks’ and create three new webhooks, one each for the datastreams V7, V8, and V9, based on the information shown in the images below for V7, but substituting your Particle device ID and access token. The only difference between the three webhooks is the assignment of the V7, V8, and V9 datastream to the webhook, and the webhook name.
After you are finished configuring each webhook, click the ‘Test webhook’ to verify it doesn’t throw an error (it won’t send the datastream value here, so don’t expect to see the LED on your Particle device change). Click the ‘Create Webhook’ button to save it and close the dialog.
Note that request quota is ‘1 per minute’ so any datastream value changes faster than one minute will be ignored (webhook won’t execute).
Full System Test
Everything is now configured to push data from either the Blynk web dashboard widgets or mobile app widgets to the associated Blynk webhook. The webhook will execute a HTTP POST to Particle’s API, and call the Particle function running on the Particle device.
Make sure your Particle device is running and connected (cyan LED breathing). From the Blynk web dashboard, send a command from one of the widgets to turn on the Particle device LED. Wait 60 seconds, and then use the same widget to turn the LED off. The label widgets on the web dashboard will display the actual datastream values. Repeat the same tests from the Blynk mobile app.
Wrap Up
This article showed how to securely control a Particle device from either a Blynk web dashboard or mobile app. No code was needed to create the Blynk web dashboard, mobile app, or Blynk webhook. Three different types of Blynk datastreams were employed in this example, demonstrating how different web dashboard and mobile app widgets can be used to accomplish the same type of remote control. Although only a state change of either on or off was used, it is easy to see how a few changes could be made to cause a variable change at the device, such as changing the LED brightness or color.
By combining what was demonstrated in this article and the prior How to connect a Particle device to Blynk, you can achieve bidirectional communication between a Particle device and both a Blynk web dashboard and mobile app. Additionally, Blynk provides a wide variety of widgets for visualizing data from a Particle device, and no-code Blynk automations can be configured to create a number of custom notifications.
