Adding WiFi to any project can be difficult. There are a few off the shelf options that make it easier. One option is the official Arduino WiFi shield. This full-featured shield uses its integrated microcontroller to handle the WiFi protocol, security, and the TCP/IP stack for you. From “plug it in and go” perspective, this is an awesome option for Arduino-based projects. Plenty of example code supports the nicely designed hardware. The main downside to some people is the price.
The more popular option these days is the ESP8266, typically advertised around $5US. They are about the size of a TO-220 packaged transistor. How do they get so small? Using a technology known as “System On a Chip”, or SOC, these tiny modules pack everything on the Arduino WiFi shield inside of a single chip! SOCs are great when space is limited. If production volumes are high enough, there can even be a cost advantage.
After spending some time with an ESP8266 I bought on eBay (which I don’t recommend..), I’ve found some things you need to know before building your ESP8266 based project.
1. Not Breadboard Friendly
Most modules come with male pin headers pre-soldered. However, the pinout makes it impossible to plug directly into a breadboard. This pinout style means you are going to need to use jumper wires. You might be thinking, but why do you need a breadboard? Isn’t this an entire SYSTEM on a chip?
Yes, but there’s still some stuff missing.
2. Not 5V Compatible
The ESP8266 modules are based on 3.3V power and I/O (aka 3v3) . If you are going to connect the ESP8266 to an Arduino, LaunchPad, or any other 5V-based Microcontroller system, you’ll need to do some logic conversion. Directly connecting to 5V I/O, like that from an Uno, can destroy the I/O of the sensitive ESP8266 chip.
See the section below on the connection nightmare for an example diagram.
3. Power Hungry
Don’t be fooled into thinking that because the board runs at 3.3V or has a small footprint that it is a “low power” device. The current draw is high when WiFi runs. In my tests, I saw my little board draw over 50mA while idle. When WiFi went active, there are large spikes.
The built-in regulator on an FTDI chip or even the slightly larger 3.3V regulator on an Arduino board is not enough. You need to use a dedicated 3.3V source or dedicated, high current, regulator. When trying to power from my Uno, my ESP8266 would not boot and I got no blinking blue lights.
4. Two ways to use the ESP8266
Keep in mind that inside of that SOC, is a microcontroller. When powered, these little boards are running some code or firmware. The default firmware that ships allow them to work as a “UART to WiFi” adapter.
However, it is also possible to overwrite this firmware and make the board do something else.
UART or Serial Interface
The default firmware makes it relatively easy to add WiFi to a project. Open up a serial port at 9600 or 115200-baud and you can start sending ASCII string commands. What kind of commands? So-called “AT-Commands.”
Back when computers used modems to communicate at 300 baud, the Hayes Corporation created a command set that the industry quickly adopted. The Hayes command style is still used today, even though Hayes is long gone. (In fact, your super modern smartphone uses it…)
It works like this. The types in a command and gets response. Hopefully like this:
AT -something OK
Sometimes, however, it’ll say:
Then you have to figure out what you (not the modem) did wrong.
That is how the ESP8266 communicates, by default, with the outside world. Using this handy ESP8266 command chart, you can see the different types of commands. It is relatively straightforward, for example, to list all of the WiFi Hotspots it detects, Connect to One (even if it has WPA2), and then send a raw HTTP request to our friend google.com.
AT OK AT+RST OK AT+CWLAP 6,”Hi There”, -85, “f8:7b:8c:1e:7c:6d" AT+CWJAP=“Hi There”,”-yeah-right" OK AT+CIFSR 192.168.1.249 OK
Crude but effective.
The second use model is to program directly the microcontroller inside of the ESP8266 SOC. In fact, you can even use the latest Arduino Board Manager to install support for ESP8266s into the Arduino IDE. So if you are familiar with Arduino, this sounds great. Just install support, write your code, connect the board, and upload.
Connecting the ESP8266 is a nightmare
The third step in that sequence, connect the board, is the problem.
Most of the common ESP8266 modules are NOT designed for external programming. The intended use is a low-cost Serial/UART communication. Some of the signals from the SOC may not be broken out and to save cost passive components like pull-up and pull-down resistors are missing.
Here’s a schematic of the extra hardware necessary to make it possible to program a cheap ESP8266 through the Arduino IDE.
Yikes! What a mess!
Even after doing all of that I still couldn’t get my module to program through the IDE. Eventually, I gave up and decided to look for alternatives.
There are Alternative Boards
Vendors like Sparkfun, Seeedstudio’s Grove UART WiFi, and Adafruit HUZZAH make their own variants of boards based on the ESP8266. They all carry a higher price tag than the cheap boards found on eBay.
The difference is property connected signals, clean breakouts, and strong vendor support. I ordered some boards from Adafruit after writing this post, and can’t wait for them to show up.
If you are just getting started with the ESP8266, I highly recommend going with one of these boards first. You can always switch to the lower cost boards once you get your project going.
The IoT fever has hit the maker community with the availability of the ESP8266. As long as you understand how it is powered, how it connects to a circuit, and the difference between ESP8266 boards, adding WiFi to any project is a breeze.
For more information check out this vibrant ESP8266 Community Forum.
Another excellent resource is this NURDspace ESP8266 Wiki page.