Thursday, March 26, 2015

Yet another esp8266 article

When I received my ESP-01 module, I didn't expect I'd end up writing a blog post about it.  Unless you've spent the last six months on a research mission in Antarctica, you probably have read about these cheap and relatively easy to program Wifi modules.  But as I learned a few things that I haven't read about, I decided to share my knowledge.

The first thing I learned is that the module worked fine getting it's power from a PL2303HX USB-TTL module, despite many claims I've read that the esp8266 modules draw too much power.  This is likely true for FTDI USB-TTL modules, as the internal 3.3V regulator on them is only rated for 50mA.  The the regulator on the PL2303HX is rated for 150mA, and my testing revealed the modules will output more than the ~200mA maximum required for the esp8266 with minimal voltage drop.  I did find the high current draw when I connected power to the ESP-01 sometimes caused the USB-TTL module to reset.  This was resolved by soldering a 22nF capacitor between the 3.3V output and Gnd.

As most guides will tell you, CH_PD/CHIP_EN needs to be high in order for the module to boot, so I soldered a short wire to Vcc.  Some people also say to pull RST high, however, like many MCU's, the esp8266 has an internal pull-up on reset, so no external pullup is required.  Similarly, GPIO0 and GPIO2 need to be high to select boot from SPI flash.  GPIO0 has an internal pull-up on boot, and GPIO2 defaults to high, so nothing needs to be wired to these pins.

An easy way to tell if you ESP is working is to do a Wifi scan.  After I powered it up, I could see an open access point named ESP_XXXXXX, where XXXXXX is part of the MAC address.

To communicate with the ESP-01, I started by using Putty at 9600bps to try using the AT commands.  I wasn't getting any response when I typed, so I reset the module by touching a resistor between Gnd and RST.  This caused the blue LED to flash, and along with a bit of garbage, the following text appeared:
[ Version:]

What I eventually figured out was that the esp8266 requires all AT commands to end with CRLF.  Putty seems to send just CR for [Enter], so I entered <CTRL-M><CTRL-J> in order to send a CRLF.

I decided to try the nodeMCU eLua firmware, so I jumpered GPIO0 low, and ran the nodemcu-flasher.  After the firmware was flashed, I was able to connect (still at 9600bps) with putty and enter elua code.  The next step was to try an IDE for elua development on the esp8266.

I found three different IDEs, LuaLoader, Esplorer, and Lua Uploader.  I tried LuaLoader first, but had problems with serial communications - I wasn't seeing any text coming from the esp8266.  It's handy DTR & RTS control buttons worked, as I could get the module to reset by wiring RTS to reset on the module, then toggling RTS low then back to high.  I tried running Esplorer, but when I found out it needs Java SE installed first, I moved on to trying Lua Uploader rather than waiting for the Java runtime to download and install.

As can be seen from the screen shot above, Lua Uploader is rather spartan, but it worked fine for me.  By default it loads with a blink program that toggles GPIO2.  Communication with the ESP is rather slow at the default 9600bps, so I saved the following init.lua file to the ESP for 115.2kbps communication:
uart.setup(0, 115200, 8, 0, 1, 1)


I'm impressed with the capability of these little modules.  Next I plan to get another module with more GPIO, and try out the C SDK.

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