Thursday, January 8, 2015

Wi-Fi revisited with the ESP8266 chip

The new ESP8266 chip has created quite a buzz in the recent months, and I have decided to give it a try for Wi-Fi communications between my instruments and a Nexus tablet. The ESP8266 is a 3 $ chip that can be programmed as a Wi-Fi access point (AP) as well as as client for a router (STA) at the same time if required. It can even host a small Web server. An SDK (Software Development Kit) is available to configure the microprocessor to specific needs.

In my case, I use it as UDP server to send the serial output generated by my system. The UDP packets are sent at the 10 Hz rate, and contain a payload of 76 bytes (mostly measured and calculated values in floating-point format). The payload contents are described here. And how the calculations are made is described here.




The Nexus tablet is programmed as a UDP client, connected to the ESP8266 AP network visible to any Wi-Fi device. When the tablet software sends a ‘START’ message to the ESP8266, it is bombarded back by the 10 Hz packets until it sends a ‘STOP’ message. These data are used to refresh the displays in real-time on the tablet. Many different custom displays can be swapped around. Any resemblance to recent professional first-class displays is not coincidental: the Android graphics capabilities are impressive.

Here is the prototype arrangement used. The ESP8266 is a 3.3V device, and a logic level converter is used on the 5 V serial signal from the system.




For development with the SDK and programming, I used this Eclipse-based tool-chain, on a Win7 64-bit machine: Espressif DevKit for Windows.




5 comments:

  1. Your posts are inspirational and very useful, thank you! I am building a small yacht and have decided to do as much of the electronics as I can myself. Apart from the cost savings, I will need to learn a great many new things to get this right, I have no real knowledge of electronics, micro processors and the last time I programmed anything I was in varsity and using fortran! Still, I am figuring a lot out as I go, but I need a point in the right directing with respect to your graphics on your displays. How do you do the graphics on computer and in android?

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    1. Richard, for PC applications, I have used both:
      Microsoft Visual Studio 2005 (C++ with MFC classes), and Microsoft Visual C++ 2010 Express.
      For Android, I use Android Developer Tools (Java).

      In all these environments, I am using the same approach:
      - a thread is continually monitoring the serial input from the instruments, and when a complete data packet is received (10 times per second),
      the main thread is asked to refresh its graphics view through an 'invalidate' command
      - the main thread then draws in memory the next image to be displayed, using the new data, and when finished, splashes the new image on the screen, creating a movie-like experience at 10 Hz.

      For several displays, I re-use a background image to which I add the needles and numbers corresponding to the current data.

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    2. Thank you. I'm going to focus on the hardware side first, but already starting to look at the options you mentioned.

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  2. Hi, I've just about completed a project converting my old wind and boat speed sensors to output NMEA and then transmitting the info via a ESP8266 01.
    Can you give me more details regarding you nexus app and where or if i can download it:

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    1. Hi Chris, my source code for the app is always changing and never in an acceptable form for publication. In this blog, I try to illustrate the main ideas and leave the details out for clarity. If you have a specific task in mind, let me know what you want to achieve and I may provide some useful feedback or directions.

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