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 🙂

RF to Zigbee gateway

The last piece of missing hardware is finished. The picture below shows the 2nd RF to Zigbee gateway I had to make to be able to receive all the Hydronic balancing sensors I made earlier this week. One of those sensors just couldn’t make it through 3 walls all day long, so I created  a temporary solution on a breadboard to solve this.

A very simple yet effective way (for me) to get the sensor data where I want it (in my Domotica system) with minimal effort.

The JeeNode acts as a RF receiver and just echoes everything with a valid CRC to the Digi XBee; from there it eventually arrives at my Zigbee Coordinator with which I can communicate over TCP/IP.

The JeeNode runs a slightly modified version of the RF12Demo sketch made by Jean-Claude Wippler. I used the NewSoftSerial library to create an additional Serial port, and added a few print statements for the XBee port, right there where the RF12Demo Serial.println()’s the received RF data to the Serial port. Compile, Upload, setting the RF band,  group- and node ID and I’m done!

This JeeNode is powered by a 5V USB adapter and the XBee gets its power from the 3.3V JeeNode ports. The XBee uses a Zigbee End Device AT firmware (2864) with the Sleep Mode set to Pin Hibernate. But because pin 9 is wired to GND, this means that the XBee is permanently on.  Only 3 wires are needed to connect the XBee to the JeeNode: 3.3V, GND and a JeeNode digital pin to the XBee DOUT.

That’s it – moving on with where this all started with: understanding the flow of  heating energy in our house!

HB sensors finished and installed

Almost ready to start investigating hydronic balancing (HB) … 😉













Everything is in place and working except for 1 sensor, which is too far away from the receiving JeeNode (which forwards all the data to my Domotica system). So I’ll have to build another RF receiver for that; the missing parts will arrive tomorrow I hope. In the meantime I started creating a webpage to display all the information I want to observe, so I don’t have to switch between browser tabs and go from one page to the other. Another thing that has to be done is program the thermostat, so that the boiler will have to burn at full power for a few hours every day, so that I can see what happens.  I’ve already seen some things that need to be adjusted!


Hydronic balancing

This weekend I came to the conclusion that whatever I do, I’ll never get a well performing central heating without hydronic balancing. I’ve been watching how the temperatures in all the rooms of our house react and where the energy goes to – it’s a mess! No matter how well I’ll be able to control the kettle, temperature control in all the rooms will still be a mess without a hydronicly balanced system.

So this weekend I decided to stop what I was doing (building the Opentherm Gateway) and first try to do something about this balancing issue.

Hydronic balancing is not something I’m familiar with, and I certainly don’t have the tools for it ; but what i can do is provide enough information with these sensors; I don’t know if I’ll succeed, but it’s worth to give it a try.

Sensor for Hydronic balancing The first thing I need to know is how much energy flows through the radiators. Well, I can do that, I guess… A JeeNode with RF transmitter and 2 1-Wire DS18B20 sensors can provide me information about how much energy each radiator produces by measuring the flow- and return temperatures of each radiator.

I’ve got a bunch of JeeNode kits still waiting to be used, enough 1-Wire sensors, batteries and all other components needed, so what am I waiting for??

So this weekend I built a first sensor and a RF-to-Zigbee ‘gateway’ so I can receive all the sensors without the need of USB, RS232 or an additional Ethernet port.

The first sensor is operational now; more will follow!

Red = flow temperature, Blue = temperature drop

Building the sensor hub

The basic ideaBecause I’m working on 4 different things simultaneously, all 4 of them are not progressing as fast as they could. And this new sensor hub is not top priority, so sometimes it takes a while before I can spend some time on it. The last few days I came up with some basic idea; this is what I have in mind for my sensor hub.

The lower side of the enclosure will have all the connectors for power and other wires to the sensors and the upper side is where a small 5V power adapter with USB connector (of which I bought a couple recently, for only 5 euro/piece) and cable will provide the necessary ‘juice’ to the Arduino Fio.

The FTDI breakout on the left is just for uploading sketches (and for power, while it’s still here on my desk).

Inside the enclosure there’s a half-size (400 points) breadboard with double-sided tape that will hold the Fio and the required wiring. Cheap and simple; and since this setup will take care of 4 of my all-in-one sensors, I can live with the fact that it’s not battery powered. This certainly doesn’t mean I’ll never build battery powered sensors anymore…

First sensor finished and working

Power wiresToday I finished soldering a cable to my first new All-in-one sensor with motion, temperature and light. Phew, after soldering those 7 wires my eyes really needed a break, even though I used a magnifying glass. The very first thing I did was getting rid of the headers for the H/L jumper; I reduced the 2headers I needed to 1 mm and added a drop of solder in between; the unused header was cut away completely. This gave me some more free space  for the black wire which connects the GND pin of the PIR to pin 1 (GND) of the DS18B20. After that I connected DS18B20 pin 3 (Vdd) and one leg of the LDR to each other so that I only needed 1 wire for supplying both sensors with power by connecting those to the + pin of the PIR; this is the red wire.

Now all the sensors were connected with each other in a way that when I would apply power to the PIR pins, the rest of the sensors would be powered as well.

Connecting the cable

As you can see a CAT5 cable was used; I only needed a total of 5 wires for this sensor. First I needed a way to glue the cable to the top cover of the enclosure; I saw there was some space between the PIR PCB and the top cover, so I what I did was remove the outer isolation on one half of the cable but left the other half intact. I added a drop of hot glue to it and quickly pushed it between the PCB and top cover, which made the cable isolation work like some sort of pull relief. Soldering the 5 wires was the last thing I did; cause now it was time to check some things first – does it work??

I wrote a small sketch that would read all the sensors once a second and display the results (do I hear a drum roll? ;-):

10765455 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=643
10766546 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=640
10767638 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=640
10768730 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=645
10769821 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=653
10770913 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=657
10772004 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=663
10773096 Motion:no,  Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=661
10774188 Motion:YES, Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=666
10775279 Motion:YES, Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=668
10776371 Motion:YES, Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=663
10777462 Motion:YES, Addr:28-98-C9-AF-2-0-0-A3 Temp=25.25 grC, LDR=660

It works! Maybe I’ll put some drops of hot glue here and there to make it all slightly firmer and than I can close this sensor.

The sketch is still very basic; it’s just some Serial.prints you see here, no wireless transmission is done yet and there’s an ugly delay(1000) in the loop() for the 1-Wire delay that I have to get rid of.

And I don’t need temperature and light sent to me every second; but waiting one second before motion is detected is way too long of course. Using interrupts for detecting motion is better I guess… soon I’ll know more about that, cause I need to be able to handle 4 PIRs (on 4 different input pins), but I can’t have 4 ISRs (Interrupt Service Routines); but the ‘solution’ will probably suffice. Sounds like a nice subject for another post.

A new all-in-one sensor

All-in-one sensor

Large sensor? Neh, I don’t think so; the image above will probably display the enclosure larger than life – well, on my 23″ screen it does 😉 The dimensions of the enclosure are 44 x 30 x 16 mm and it houses a PIR, a Maxim DS18B20 and a LDR.

Motion, Temperature, Light. That’s what I think I’ll need for my new sensor. Humidity will be left out; although I do have humidity sensors in my house, I don’t use them that much. For the bathroom a humidity sensor would be nice, but not for the rest of the rooms upstairs. Cause that’s where this new sensor is going to be used; at least 3 of these, one for each room and a slightly different version for the bathroom.

I’ve used this enclosure before with other PIR sensors, but this time I wanted to see if there was enough room for some more; I must say, it’s a bit crowded inside the enclosure now. The PIR has a PCB whose dimensions are 32 x 24 mm and it has lots of components, so I really need the 16 mm depth of the enclosure.

The PIR I’m using has a detachable lens, so after carefully measuring where the center of the 12 mm hole should be drilled through the cover of the enclosure, I could stick the PIR through that hole and put the lens back on the sensor. I did have to cut away some wires on the PIR side of the PCB, cause otherwise the distance between the PCB and the top cover of the enclosure was too large. After that, the PCB was glued to the top cover of the enclosure.

For the 1-Wire DS18B20 and LDR I drilled 5 x 0.5 mm holes, put the legs of these 2 sensors through the holes and fixed the legs with a tiny drop of glue, just enough to keep them in place. The housing of  the DS18B20 sticks out of the enclosure very little; you don’t see the legs sticking out. The LDR sticks out a bit more, so that the LDR won’t be hindered by any shades from the DS18B20.

What's inside

Well, that all for now – now I’m facing the fact that I have to solder these 3 sensors to a single cable that has to enter this crowded enclosure somewhere… phew, what am I getting myself into?.. I hope this won’t get too messy 🙂


Something old and something new

While I’m logging data and waiting for it to become substantial enough to test another project with, I thought it would be nice to kill the time and start building some new sensors: motion, temperature and light.

My goal is to monitor the complete second floor. For the 3 bedrooms I want to monitor motion, temperature and light. The passage will only require motion and light, while measuring the humidity in the bathroom would be nice too.

So, for that I need the following:

  • 5 * motion;
  • 4 * temperature;
  • 5 * light;
  • 1 * humidity.

I already have the motion sensors (PIR), the temperature sensors (1-Wire DS18B20), light sensors (LDR), enough JeeNodes, so all I need is a new humidity sensor.

OK; the amount of sensors I want to use is a bit too much for a single JeeNode I guess. Maybe 2 JeeNodes will suffice? I didn’t do any math on this yet, but I don’t think a single JeeNode can do the job all on its own. 2 JeeNodes maybe, cause the temperature sensors can be on a single 1-Wire bus, so those sensors won’t use up much ports on the JeeNode; and maybe I can use an Analog Plug to measure the LDRs? We’ll see. But for now, I assume I’ll need more than 1 JeeNode. However, I don’t like to spend an XBee module on each of those JeeNodes, cause I want to keep it relatively low cost. Yeah I know, there are cheaper alternatives for XBee..

But wait, I’ve still got an Arduino Fio; I’ve bought it sometime in January, not for a specific purpose but just to have a look at it, and I never found a good use for it yet. This Fio is also based on the ATmega328P and runs at 3.3V and 8 MHz. And it also has an XBee socket and USB connector. And it’s getting old, gathering dust on the shelf…

Now why don’t I use this Fio as a ‘hub’, or ‘central node’? It shouldn’t be too hard to make the (1,2,..) JeeNodes talk to this Arduino Fio over a few wires and use the Fio to transmit all the sensor values to the Zigbee coordinator; now that would be nice! I could power this Fio with a small USB power adapter and run a few wires (for power and serial connection) to the JeeNodes. Maybe I could just as easily use 1 JeeNode per room; this leaves enough ports available for future expansion… well, let’s think this one over for some time!

Half-way there?

Today I changed some things on my previous setup, after testing & concluding that XBee IO Change detection doesn’t work during sleep, which I already anticipated.

I changed some settings in the XBee and I added a wire to Pin 9, the Pin Sleep Control Line. The XBee is now in Sleep Mode 5 (Cyclic Sleep Pin-Awake), which means the XBee wakes on timer expiration or when Pin 9 changes from high to low state. The latter (Pin 9 change) is what the extra wire is for; it connects the output of the Hall-effect sensor to Pin 9, so that when the sensor output changes, the state of Pin 9 changes also.

Now the Xbee sends an IO Data Sample frame each 28 seconds based on the sleep settings, but also when the magnet is being moved towards the sensor – because the XBee Pin 9 becomes low, the XBee wakes up and starts to send an IO Data Sample Frame. Great! So now I know instantly when the magnet comes close to the sensor; exactly what I need.

But that’s only half of what I need of course, because when the magnet is being moved away from the sensor, the sensor output (and XBee pin 9) changes back to high, but that’s not triggering a wake up of the XBee… hmm.

So I started searching the net and read about all kinds of latches, NOT gates, flipflops, and saw more circuits than I’ve never seen before in my life. I haven’t found what I’m looking for yet – I don’t even know if it can be done – but I’ll continue my search for a way to shortly ground the XBee pin 9 whenever the sensor output changes from high to low or vice versa.

Yeah I know, an ATMega, duh.