One of the humidity sensor currently in use, on the Home Automation Project, is the ubiquitous DHT22 also known as AM2302 which came with the AirPi board I installed.
I don't particularly like it as it has a very specific protocol which need a special C-compiled software to communicate. Second problem, it sometimes crashes. And lastly, I am starting to have serious doubts about its accuracy (specially on the humidity side).
I discovered an alternative known as SHT21 or HTU21D (depending on the manufacturer) which seems quite appealing as this one use the perfectly standard I²C protocol.
That said, the chip is so tiny, the only way to use it is mounted on a breakout board (like the GY-21): For around 4€, you get the sensor, the power regulator as well as a level shifter. Which means that it can safely be used with 3.3V or 5V.
More information and datasheets
Datasheets and examples in C can be found on the manufacturers' websites:
Basically, it works by sending a Read (humidity or temperature) command, wait (hold mode) or poll (no hold mode) for the answer and apply a mathematical formula to get the actual value.
There is a precision setting but the only effect is to reduce the measurement time and since on the default/highest setting it takes less than 50 ms, there is little need to change it.
Using it with Arduino
As I wanted to experiment with the ESP8266, I (temporarily) diverted the chip from its initial goal (i.e. replacing the DHT22) and decided to use it on the Arduino plateform. There are librairies available from Adafruit or Sparkfun but I created my own version to include soft reset as well as serial number reading.
I'll publish it as an example at some point in the future.
Later, using this chip on the Rasberry Pi with python should be trivial.
First impressions
So far, the only small drawback I found with this kind of chip is the fixed I²C address (0x40) which mean there can only be one sensor per bus. But in practice, there is little need for more than one anyway.
As noted before, the devkit comes with a USB connection and power regulator. Same principle as on the Arduino boards.
The version bought is the newest devkit 1.0 (AKA v2 on Seeedstudio).
OK... bizarre but a quick check with Google gives a workaround:
file.remove("user.lua")node.restart()
According to one post, there are two Lua files inside a new board: init.lua and user.lua.
These are used for factory testing purpose only. Now the message has become:
And for information purpose, the content of the "init.lua" file:
>file.open("init.lua","r")>print(file.read())--init.lua, something like thisprint("Will run user.lc/user.lua in 1000ms")tmr.alarm(0,1000,1,function()tmr.stop(0)locals,erriffile.open("user.lc")thenfile.close()s,err=pcall(function()dofile("user.lc")end)elses,err=pcall(function()dofile("user.lua")end)endifnotsthenprint(err)endend)>file.close()
So far so good...
Connecting to the Internet
Same procedure as last time:
Setting "Wifi Station" mode => OK
Registering SSID and password => OK
Obtening a IP address => OK
Connecting to an external website => variable
Connecting from a browser to the module => KO
For some reason, there is a incompatibility between most firmwares and my Wifi router. :-(
Time to try with a different/more recent firmware.
Flashing disaster
As we say in french "Never Two Without Three". So after the HM-12 and the ESP-201, something was bound to go awry!
Using the latest version of esptool, I uploaded a new firmware... flashing was reported as successful but the module couldn't even boot! And this was the case with all firmware I tried.
As as I discovered, this is because the devkit 1.0 is based on the ESP-12E board. The "E" letter is important as it means the flash is 4 MB (or 32Mb) instead of the 512 KB (2Mb) standard model. The mechanism address the flash seems different and it is essential to use specific parameters like:
I.e. using DIO for flash_mode (instead of QIO) and 32Mb for flash_size (instead of 2Mb).
Then, at least I could boot! But the filesystem (used by LUA) was destroyed and the list of files was returning strange data.
It took me long while to find a way clear it (obviously file.format() didn't work) but I, at last, managed it by running:
./esptool.pyerase_flash
That said, it is still impossible to open any file from LUA. There are a few comments about this problem on the Seeedstudio page, so I am not alone.
I actually wonder if the nodemcu builds are truly compatible with this new hardware!
EDIT (02/07/2015):
Many thanks to Johny Mattsson for his workaround to this issue and for taking the time to notify me. I am happy to report that the new esptool.py (on dev branch) now unlocks the filesystem. See pull-request note Workaround write-protected flash when using esptool.py to flash in DIO mode for more information.
New access point
I happened to have a spare (old) wifi router.
And with this new set-up, TCP connections were fine either as a client or as a server!!!!
How annoying (and unpractical as I don't really want to multiply routers). And also what a waste of time and energy.
Since all types of firmwares (AT, nodemcu, arduino's) are plagued by this problem, it might be link to the Espressif's SDK I presume. But I still can't pinpoint what exactly is happening and why some IPs are reachable while others are not.
At least, I could play with my two modules.
The story so far...
2 modules 'ESP-201' and devkit 1.0 (using an ESP-12E)
Can't use my main Wifi Router but works fine on another one (except with a very old original firmware for the ESP-201)
LUA Filesystem broken on the devkit 1.0 (haven't retried on the ESP-201) making the use of nodemcu very unpractical
Like this blogger, who seems to have quite a lot of experience on ESP8266 modules, I am now convinced that Arduino's ecosystem is the way to go, at least for now.
Having disconnected the GPIO0 and rebooted the module, the serial console was all black. It seems that speed was now down to 9600 bauds... fair enough.
First steps with the LUA console
I don't really know LUA. Fortunately, the API is documented and there are examples available on the main website.
>print(node.info())095103111471261768512040000000
OK Version is 0.9.5 as expected. Other values are chipid(10311147), flashid(1261768), flashsize(512KB) and flashspeed(40000000). Don't know how important they are in our case.
Cool... changing firmware didn't reset the Wifi configuration! :-)
Second problem...
Depite the display of the IP address... the module didn't seem connected! :-(
Well, after a lot of investigation, I discovered that UDP usually works, ping doesn't (it might not be implemented, I don't know), and for TCP... it depends.
As first, I thought it was related to a ARP (MAC address) bug described in some forums because I too could't communicate with a machine on the same LAN. But it turned out that even with remote sites (all routed through the same gateway), sometimes it worked but most of the time it ended up in timeout. It looked like the ACK (last part of the TCP handshake) wasn't accepted by the module.
I probably tried every firmware available, including the development ones, to no avail.
Pity, this looked liked a potentially interesting product. And by the way, if official website is not informative, the Github project page has all the links.
ESPlorer
On a positive node, during this exploration of nodemcu, I discovered a Java software which facilitate the use of the module.
It is called ESPlorer and can deal with the "AT mode", Nodemcu and (in theory at least) Micropython.
Micropython
Next...
Following the instructions from the Micropython Github's page, I installed esp-open-sdk in order to compile the firmware. Unfortunately this doesn't seem to work anymore. I always ended-up with errors related to implicit declaration of function 'PIN_PULLDWN_DIS'. It seems that these macros have been removed in the Expressif SDK 1.1. Great!
Since I only wanted to give a quick try, I was trying to avoid having to waste too much time on compiling this firmware!
Fortunately, the good folks at Adafruit have a compiled version ready to download.
But, sadly enough, once configured I found the same problem I had with nodemcu... I can connect to some external website but there is still this weird issue with any local website. Worse, this makes Micropython crash!
I think MicroPython has a lot of potential but it is still very much work in progress.
Note : In the meantime, I "ordered" a WiPy during their Kickstarter fundraising. It is not based on the ESP8266 but on the CC3200 which is not in the same league in terms of performance, support and price.
Back to AT Firmware
Unable to solve the TCP connection kerfuffle, I decided to flash an AT firmware, thinking that using nodemcu may have broken something.
Version 0.9.5.2 didn't seem to recognise the Wifi network at all any more but the 0.9.5 booted:
AT+GMR00200.9.5(b1)compiled @ Dec 25 2014 21:40:28AI-THINKER Dec 25 2014
That said, once again UDP connexions were fine but TCP ones were also a bit dodgy (same as with nodemcu and micropython). They used to work fine! Same for ping which was no longer possible.
Trouble is, when looking for information, there are loads of info about "ESP8266 + Arduino board" (linked by Serial) which is not the setup used here (ESP8266 used as sole MCU programmed by the Arduino IDE tool-chain).
Also without any kind of "assistance" (keep in mind that the Arduino boards use a dedicated MCU just to help with the USB connection and the flashing process) it is not as straightforward as flashing an Arduino: you need to play with GPIO0 and Reset. That said, thanks to this I understood the concept of devkit mentionned by nodemcu. More about it later.
Back to square one
Not being able to run anything because of this strange bug, I decided to see if the module was beyond repair (cf what happend with my HM-12).
For this, I managed to track down the original firmware contained in a file called ESP8266_flasher_V00170901_00_Cloud Update Ready.zip. And... Miracle! the client/server fonctions were back...
So just to make sure, I thought:
Let's try again MicroPython.... Nope! (same behaviour as before)
Let's try again Nodemcu 0.9.6 (I'm becoming good at flashing :-) )... Nope! (idem)
In short, the only firmware which seem to work on my (all?) ESP-201 seems the one reporting "00170901". Sadly enough, this one is not massively stable nor really useful in standalone.
Next time ?
Looking for additional info, I discovered that the nodemcu's devkit exists in 2 (released) versions:
the v0.9, which is wide-ish usually blue (yellow for clones) and doesn't seem to work on Macs (I personally don't care but some people might)
the v1.0, which is narrower, usually black, called v2 by Seeedstudio and is supposed to be Mac friendly.
I don't exactly know how different they are otherwise. They both have USB connection, voltage regulator and 2 buttons to help with flashing : FLASH & RESET.
So I decided to order one v1.0 from ebay ~ US$11 (inc. P&P). Should arrive within 3-4 weeks.
In the meanting, I'll try to explore deeper the possibilities of both nodemcu and arduino on ESP8266 without using network connections.
The latest craze in Wifi cheap circuit is the Expressif ESP8266 which can be found on a quite a few breakout boards.
ESP-201
With so much choice and without having taken the time to think much about it, I went to the ESP-201.
This one as a "normal spacing" (1/10th inch) pinout and is dead h: US$ 3.70 including postage.
As noted by numerous people, the 4-pin header is not breadboard friendly at all and pins need to be either resoldered on top or bent a bit.
The details of all the pins of the board is available on this blog entry.
Wiring
Re-using Jeelab's USB FTDI board and an aditional 5V to 3.3V voltage converter, I connected the board the following way:
3.3V & GND
TX <-> RX
RX <-> TX
(GP)IO15 <-> GND
CHIP_EN <-> 3.3V
(GP)IO0 <-> GND when flashing (left unconnected otherwise)
USB Connection
with minicom for starters @115200 bit/s (but it really depends on the firmware apparently usually 9600 or 57600).
Some tests
On the console:
AT+CWMODE=1OKAT+RSTOK ets Jan 8 2013,rst cause:4, boot mode:(3,5)wdt resetload 0x40100000, len 212, room 16tail 4chksum 0x5eload 0x3ffe8000, len 788, room 4tail 0chksum 0x1cload 0x3ffe8314, len 72, room 8tail 0chksum 0x55csum 0x55jump to user1readyAT+GMR00170901OKAT+CWLAP+CWLAP:(0,"",0,e0:5e:ff:3f:00:00,0)+CWLAP:(2,"SSID-01",-83,14:0c:76:fa:70:6c,1)+CWLAP:(0,"FreeWifi",-88,14:0c:76:fa:70:6d,1)+CWLAP:(2,"FREEBOX_NAIMA_SO",-92,0e:76:6b:29:10:48,1)+CWLAP:(0,"freephonie",-92,0e:76:6b:29:10:4a,1)+CWLAP:(0,"FreeWifi_secure",-85,14:0c:76:fa:70:6e,1)+CWLAP:(3,"SSID-03",-81,f0:82:61:d0:52:ac,11)+CWLAP:(0,"FreeWifi_secure",-95,f4:ca:e5:c9:1c:82,11)+CWLAP:(2,"freebox_Jeannot",-90,f4:ca:e5:c9:1c:80,11)+CWLAP:(2,"FREEBOX_TONY_55",-86,68:a3:78:01:be:46,5)+CWLAP:(0,"FreeWifi",-89,68:a3:78:01:be:47,5)+CWLAP:(0,"FreeWifi_secure",-88,68:a3:78:01:be:48,5)+CWLAP:(4,"Bbox-8735B701",-84,d0:84:b0:0e:be:a0,11)+CWLAP:(0,"SFR WiFi Mobile",-87,d2:25:15:dd:b6:2f,6)+CWLAP:(2,"SFR_B628",-78,00:25:15:dd:b6:2c,6)+CWLAP:(2,"freebox_SWWNDE",-74,ee:de:4f:b8:6b:94,6)+CWLAP:(0,"FreeWifi",-75,ee:de:4f:b8:6b:96,6)+CWLAP:(0,"FreeWifi_secure",-75,ee:de:4f:b8:6b:97,6)+CWLAP:(0,"SFR WiFi Mobile",-90,9a:a1:d7:ec:85:af,6)+CWLAP:(2,"SFR_85A8",-88,e0:a1:d7:ec:85:ac,6)+CWLAP:(0,"SFR WiFi FON",-90,9a:a1:d7:ec:85:ad,6)+CWLAP:(3,"SSID-02",-93,20:e5:2a:0f:f1:70,6)+CWLAP:(0,"FreeWifi",-87,52:f2:79:19:0b:7a,7)+CWLAP:(0,"FreeWifi_secure",-89,52:f2:79:19:0b:7b,7)+CWLAP:(4,"Livebox-4dac",-87,00:19:70:44:cf:25,11)+CWLAP:(0,"FreeWifi",-92,f4:ca:e5:c9:1c:81,11)+CWLAP:(0,"FreeWifi_secure",-91,f4:ca:e5:bd:41:fa,12)+CWLAP:(0,"FreeWifi",-89,f4:ca:e5:bd:41:f9,12)OKAT+CWJAP="MYSSID","MYPASSWD"OKAT+CWJAP?+CWJAP:"MYSSID"OKAT+CIFSR192.168.1.20
On the computer:
nc-l5000
Connecting to the computer from the module using TCP:
