ESP8266: Good enough for a battery powered sensor?

ESP8266_power_measurements_ battery_lifeDuring the last 2 weeks I’ve collected a lot of ESP-8266 power usage charts as shown here. Enough to conclude that a ESP8266 can be used to build battery powered sensors (e.g. a temperature sensor) but how happy you’ll be after some time highly depends on the report interval. A report interval of 4 samples per hour will lead to a battery life of roughly 1 year. Increasing the report interval to 60 times an hour (once per minute) will lead to a much shorter battery life: less than 3 weeks.

The biggest problem lies in Wifi. It takes my ESP-12 about 1 … 3,5 seconds to get a Wifi connection after waking up from deep sleep. And this is by far the largest contributor to the total time needed to get a sensor value out the door. I tried several things to see if I could shorten the time needed to get a Wifi connection but had no luck; a dedicated AP for a single ESP-12, moving the AP within 2 m. range of the ESP, changing channels – nothing. Maybe turning off (WPA) security may help, but I don’t consider that as a real option. Maybe a static IP address may help (instead of using DHCP) but that’s not a real option either. Increasing the report interval of the sensor is the only thing I can think of right now to get a good battery life (of 1 year or more).

So that’s it, ESP8266 is a no-go? No way! The ESP8266 can still be very helpful in a lot of ways, I’ve had a lot of fun while exploring the ESP8266 and will definitely use them whenever I need always-on Wifi for so,me future project. And I made a nice ‘poor mans digital scope’ during all the fun as well. But it won’t work well when you want to use a relatively short report interval

Is there an alternative for the ESP8266? Lots of ’em, mine is called Zigbee. I’ve been using Zigbee modules since 2010 or so and built my own Zigbee sensors based on a JeeNode + XBee series 2 modules. For motion, temperature, barometric pressure, light intensity (lux). Batteries last about a year, that’s OK. If I would let a ESP8266 do exactly the same thing (with the same reporting interval, sensor type) as a combination of JeeNode & XBee, the batteries would probably last about 8 weeks. Wooaahhh…

I have some unused 3.3V Arduino Pro Mini’s and some XBee’s and will make some similar power usage charts of those; an XBee is ready to send in 35 milliseconds after power-up, so here the numbers will be quite different …

For those interested I’ve put together a page with some of the ESP power usage charts here, so you can see for yourself.

And now it’s time to move on … cause a new Odroid-C1 arrived on which I’m gonna play with OpenHAB, CometVisu, PencilBlue and some more interesting stuff 🙂

ESP8266 current / power usage charts

After a first test with a 4.7 kΩ resistor it was time to connect the INA219 to the ESP8266 + DS18B20 setup I wrote about some time ago. But first I extended the VB.Net app so that I could do the following with it:

  • Set a trigger value so that the app will start collecting the samples after the measured current rises above that trigger value;
  • Set the INA219 Calibration mode from the app, not hard-coded in the Python script running on the RPi;
  • Tooltips for the data points on the chart;
  • Leave a comment in a textbox and a ‘screenshot’ button to save the whole form as .jpg file;
  • Automatic Y-Axis scaling, automatic re-sampling, automatic screenshots (yeah, I love automation…)

I finished most items last Tuesday so now I’m ready to start charting the ESP8266 power usage 🙂

The setup is the same as in the post I mentioned above and I changed the code so that it would mimic Harald Kleins code as much as possible (DHT22 became DS18B20 and MQTT was added) so that we could compare our measurements: Haralds measurements were done with a digital scope + uCurrent Gold and mine with the INA219 (duh). Here’s my current chart (click the image for a larger version with a bigger chart area)  and Haralds version:

INA219 sample of ESP-8266 + DS18B20

What do we see here? A detailed analysis of what’s going on inside the ESP8266 in terms of current draw. The chart is in fact a detailed ‘power map’ cause by calculating the area (mA * milliseconds) between the blue line and the X-Axis we know the power usage for a single sample. With the sample interval, deep sleep current and the power the battery can deliver it should be possible to make a good estimate of what can be expected in terms of battery life. To be continued…

ESP8266 power analysis

mA_measurements

After a lot of hours I think I’ve finally created a way to see what’s going on in terms of power usage while the ESP-8266 is not in deep sleep. Cause that’s just as important as its deep sleep usage. Triggering data collection, getting the collected data to my PC for further processing and charting is what I’ll start working on tomorrow – what will I see once it’s working, that’s the big question right now 😉

ESP8266: testing deep sleep & interrupts !?


This weekend I’ve been testing one of my ESP-12 module for more than just a few minutes; more like a few hours. Just to see how ‘robust’ the ESP8266 actually is. The story about ‘zombie mode‘, where the module didn’t restart after the deep sleep period had ended, made me curious whether the ESP8266 was stable enough (to use at all).

So I created these 2 scripts to make it do something useful for a change:

init.lua:

FileToExecute="gettemp.lua"
l = file.list();
for k,v in pairs(l) do
  if k == FileToExecute then
    print("*** You've got 5 sec to stop timer 0 ***")
    tmr.alarm(0, 5000, 0, function()
      print("Executing ".. FileToExecute)
      dofile(FileToExecute)
    end)
  end
end

gettemp.lua:

require('ds18b20')

serv_ip = '192.168.10.168'
serv_port = 8001
gpio4 = 2
interval = 20000000
ds18b20.setup(gpio4)

function getTemp()
  temp = ds18b20.read()
  conn = net.createConnection(net.TCP, 0)
  conn:on("connection", function(socket)
    socket:send(""..node.chipid().." "..tries.." "..temp.."\r")
  end)
  conn:on("sent",function(conn)
    conn:close()
  end)
  conn:on("disconnection", function(conn)
    node.dsleep(interval-tmr.now(), 0)
  end)

  conn:connect(serv_port, serv_ip)

end                   

function connect()
  tries = tries + 1
  wifi_ip = wifi.sta.getip()
  if wifi_ip == nil then
    if tries < 5 then
      tmr.alarm(0, 1000, 0, connect)
    else
      node.dsleep(interval-tmr.now())
    end
  else
    getTemp()
  end
end

tries = 0
connect()

Nothing spectacular – it reads a DS18B20 sensor, sends the temperature and some other data to a NodeJS TCP server, goes to deep sleep and wakes up 20 seconds after the previous wake-up, so that the module does this 180 times per hour. It has been running since Friday night.

ESP8266 measuring DS18B20 and going to deep sleep

But then I found another interesting post about deep sleep and interrupts. And if my interpretation is right, this could be what I’ve been looking for – I just had to try it out:

You can easily esp8266 wake from a deep sleep. Just bring on to the RST short negative pulse. I use it.

 

Well…it works! (on a ESP-12 that is, haven’t tested any other model).

ESP8266 wake-up wire

 

Whenever the black wire at the bottom of picture makes contact with the RST pin and effectively pulling it to GND, the ESP8266 wakes up – this needs further research! 🙂

For now, I resumed the reliability test for another night.

ESP8266 in deep sleep

With the ESP-12 modules on a breadboard adapter I was finally ready for some tinkering. The plan for today was very simple: flash NodeMcu firmware, start programming the ESP8266 in Lua and try deep sleep mode.

I put an ESP-12 on a breadboard, used a FTDI-ish thing to connect the ESP-12 to my Windows PC and used a 3.3/5V breadboard power supply (set to 3.3V) to power the ESP-12.

ESP-12 in deep sleep

Flash!

Time to flash the thing! I knew that sometime in January MQTT was added to the NodeMCU firmware so I searched for a recent firmware version that contained the MQTT code. I read some rumors that MQTT seemed to be broken in the latest NodeMcu firmware releases – on the ESP8266 forum I read that v20150127 was the latest release where MQTT still worked; yesterday I read that it was due to the addition of MQTT v3.1.1 support.

Tools and other things I downloaded to get started with the ESP-12 were:
NodeMcu firmware
NodeMcu flasher
LuaUploader
LuaLoader

The latter 2 have some overlap in functionality – it looks like LuaLoader will be my favorite. OK; now that I have a flash tool and the v20150127 firmware – what’s next? After some trial and error I found out that I had to change something on the ‘Config’ page of the flash tool:

NodeMCU Flasher

I unchecked items 2, 3 and 4 and let the first item point to the right firmware image I wanted to use. Figuring this out took me longer than soldering the breadboard adapter … A wire from GPIOØ to GND followed by a cold boot set the ESP-12 in firmware upload mode, clicking “Flash” on the Operation tab was enough to flash the firmware.

After some playing around with “Hello World”- and “Blink”-like Lua scripts it was time to do something that would be a bit more exciting – things like interrupts, deep sleep and some MQTT of course.

First I wanted to know everything about deep sleep; I found this forum post and read about another mode the ESP8266 could be in – zombie mode. I wanted to avoid that mode of course so I took the suggested zombie counter measures which is pulling up GPIOØ & GPIO2 to VCC with ~5kΩ. And for using the deep sleep mode RST & GPIO16 have to be connected to each other and also pulled up to VCC; and of course CH_PD as usual.

Boot loop protection!

And of course, the first script I made with a node.dsleep() in it didn’t work .. well, it did what it was supposed to do, but not what I meant it to do! Some error in the code caused a reboot within a few seconds and there was no way I could stop this boot loop; nothing helped. Only after re-flashing the firmware I regained control over my ESP-12… So the first thing I did was searching for a workaround/solution for this and found one here, so now my init.lua (the NodeMcu autoexec.bat 😉 looks like this:

FileToExecute="printtext.lua"
l = file.list()
for k,v in pairs(l) do
  if k == FileToExecute then
    print("*** You've got 5 sec to stop timer 0 ***")
    tmr.alarm(0, 5000, 0, function()
      print("Executing ".. FileToExecute)
      dofile(FileToExecute)
    end)
  end
end

Yeah I know,  this adds an extra delay of 5 seconds after a restart, but this is much, much better than the need to re-flash each time you make a mistake – and since my experience with Lua is like 1~2 hours, I think that this will be my init.lua for a loong time.

Results for this evening: Deep sleep seems to be working… onwards!

New ESP8266 (ESP-12) modules ready

Today, while my son and I were visiting the NMM, the breadboard adapters for my new ESP8266 type ESP-12 modules arrived. Finally …

ESP12_on_breadboardI was a bit surprised by their size though; the adapter covered the whole middle area of the breadboard, leaving no room to plug in wires as you can see. So instead of using the headers that came with the adapter, I used headers with a length of 18 mm. This way the adapter board is still held at its place on the breadboard and I can use female wires to connect to the ESP-12.

Now let’s see what has happened in the ESP8266 scene during the time I was away 😉

MQTT publishing with the ESP8266 + Arduino

This is more or less a follow-up on my previous post about using the ESP8266 to MQTT-enable an Arduino (or a JeeNode in my case). The first time I installed the espduino library there was no publish available yet; one day later it was, so this afternoon I installed the latest version in the Arduino IDE and gave publishing a try.

All I had to do was adding some additional code to the example:

int reportInterval = 10 * 1000;
unsigned long now = 0;
unsigned long nextPub = reportInterval;

void loop() {
  esp.process();

  // will work for 49 days; that's OK.
  now = millis();
  if (now >= nextPub) {
    nextPub += reportInterval;
    String payload = "Payload ";
    payload += now;
    char char_array[payload.length()+1];
    payload.toCharArray(char_array, payload.length()+1);
    esp.publish("topic", char_array, payload.length()+1, 0, 0);
  }
}

The result:

Espduino libaray publishing

I noticed that the keepalive packets are still being sent even though the publishing is done every 10 seconds; I can’t recall seeing that behavior with other MQTT clients – as far as I know keepalive packets are only needed to ping the broker when there hasn’t been any other communication within the keepalive interval, but I might be wrong about that. I’ll have to check that some day.

For now this is not a real issue but it probably will be when the library will be used in a setup that’s battery powered. Another question I have is: what would be an acceptable keepalive interval for a battery operated MQTT client? For some sensors even a value of 3600 seconds would suffice I guess..

Last thing on my mind is a good auto-reconnect feature for this; a closed connection (e.g. because your Wifi AP has been down for a short period) should not be a reason to power cycle all those ESP connected devices in your house..!

MQTT client for Arduino with the ESP8266

A few days ago I saw a new (first commit on GitHub just 5 days ago) library that made it possible to use MQTT on an Arduino-ish board and use the ESP8266 Wifi Serial Transceiver to connect to a MQTT broker. I just had to try it out 🙂

ESP8266 MQTT JeeNode

I used the same setup as before cause it was still on my desk, installed the library in the Arduino IDE, checked the SERIAL_BUFFER_SIZE in [your program files]ArduinohardwarearduinocoresarduinoHardwareSerial.cpp (OK in Arduino 1.0.6, didn’t check older versions), changed the example regarding MQTT broker address, Wifi SSID & password, client id (JeeNode_on_your_desk), set the debug serial port to pins 6 & 7 and uploaded the sketch to the JeeNode.

And it’s working, as the Mosquitto MQTT broker messages show below:

D:Program Files (x86)mosquitto>mosquitto -c mosquitto.conf
mosquitto version 1.1.2 (build date 30/01/2013 20:46:29.67) starting
Config loaded from mosquitto.conf.
Opening ipv6 listen socket on port 1883.
Opening ipv4 listen socket on port 1883.
New connection from 192.168.10.155.
New client connected from 192.168.10.155 as JeeNode_on_your_desk.
New connection from ::1.
New client connected from ::1 as mosqpub/3228-devbox.

Nice! Let’s try to send an MQTT message to the JeeNode:

mosquitto_pub -h localhost -t /topic -m "Hi there, it's me!"

And the debug port showed this:

[espduino_mqttclient]
RESET ESP done
WIFI: Connected
TCP: Connected
AT+CIPSEND=36
MQTT: Connected
MQTT:Connected
MQTT: subscribe, topic
AT+CIPSEND=13
MQTT: Subscribe successful

MQTT: Send keepalive packet
AT+CIPSEND=2
MQTT: Send keepalive packet
AT+CIPSEND=2
MQTT: Send keepalive packet
AT+CIPSEND=2
Received, topic:/topic, data:Hi there, it's me!
MQTT: Send keepalive packet
AT+CIPSEND=2
MQTT: Send keepalive packet
AT+CIPSEND=2
...

And here’s what the communication between JeeNode & ESP8266 looks like:

AT+RST
ATE0
AT+CWMODE=1
AT+CWJAP="SSID","password"
AT+CIPMUX=0
AT+CIPCLOSE
AT+CIPSTART="TCP","192.168.10.179",1883
AT+CIPSEND=36
 "  MQIsdp     JeeNode_on_your_deskAT+CIPSEND=13
‚,    /topic AT+CIPSEND=2
AT+CIPSEND=2
AT+CIPSEND=2
...

Nice; not that I have any immediate use case for it (my Zigbee network based on XBee modules is still working fine), but it’s fun to see this working and good to know it exists.

Next ‘experiment’ will be an MQTT client on the ESP8266 itself (yep, without MCU). I’ve already installed the ESP8266 Windows Eclipse IDE in a VM so that I can flash the ESP8266 with a firmware that includes this MQTT client; that will be even more exciting; stay tuned!

Meet the ESP 8266 WiFi Serial Transceiver

esp8266Look what I found under the Christmas tree about a week ago – ESP8266 modules 😉

A tiny module with a size comparable to a Fibaro Universal Sensor. Basically, the ESP8266 enables you to add wireless connectivity to your hardware – to anything that does serial; for example your Arduino or Raspberry Pi. But there’s more to this module – you can build your own firmware, program it in Lua and do stuff that might make that additional MCU obsolete.

But for now, all I have to tell is about my experiences during the first few hours with the ESP8266.

After unwrapping the modules the first thing I had to find out the purpose of the 8 pins of the ESP8266 board. VCC, GND, RX, TX and found out about those really quick; I also found a small Arduino sketch that would allow me to test some basic functions of the ESP8266 so I set things up on a breadboard and uploaded a sketch to a spare Arduino.

No go.. I had been a bit too hasty, thinking that a single webpage would provide all the information I needed to get things going. After a while I found out that the CH_PD pin had to be pulled up to VCC to set the ESP8266 to ‘normal operation’ mode. Cause when pulled to GND, the ESP8266 will just sit and wait for a new firmware to arrive … OK, got that. Still no go; that’s when I read about the different baud rates – some models work with 9600 bps, others with 57600 bps so maybe the ESP8266 and the Arduino weren’t using the same bps. So I decided to just hook up the 2nd ESP8266 to my PC with a PL2303 serial to USB cable and see if I could get the module to respond to some AT commands.

ESP8266 with PuTTYPuTTY is one of my favorite tools for telnet, ssh and it can also do serial communication, so I used PuTTY to send some AT commands to the ESP8266, but after some time I gave up… I knew I was using the right speed (9600 bps in my case) but the module just didn’t respond after- no OK; nothing.

ESP8266 with TermiteChanged some settings, still no answer. Made PutTTY add an additional LF after a CR but still no luck? Eventually I switched to Termite, cause I found out that I wasn’t the first having problems with the combination PuTTY + ESP8266.

 

Now that I knew it was 9600 instead of 57600 bps I could proceed with the sketch mentioned earlier. Another ‘problem’ was that the Arduino operates @5V and the ESP8266 @ 3.3V, so I had to do something about that too; I saw all kinds of solutions with level shifters, resistors, diodes and decided to go the easy way – a JeeNode which operates @ 3.3V:

ESP8266 on a JeeNode

The result in the PuTTY window that was connected to the ‘debug’ Serial port (pins 6 & 7):

ESP8266 PuTTY screen

Neat. Needless to say that this is just a small example of what this ESP8266 can do; it can do much more than just fetching a small web page – I haven’t even scratched the surface yet! A Wifi Door sensor for the price of an ESP8266, a reed switch + magnet and power supply.. the latter is the only downside of the ESP8266: it consumes too much power to run on batteries. Well, you can’t have ’em all … (yet?) Besides that, I love this little powerful Wifi module.