Tag Archives: arduino

Ciseco XRF modules & LLAP Protocol

In my last post about counting events with Arduino and PCF8583 I talked about this “yet another weather station” project I was working on last summer. The station was deployed in the garden of a cute apartment we rented in an old “masia” near Olot, 100 km north of Barcelona. It is in the mountainside, surrounded by woods and 10 minutes walking from the near town. It has a beautiful garden with plenty of space. We spent there most of the summer but now we are still driving there on the weekends. It’s colder, sometimes freezing, and when it rains, well, it does rain. Off course it was the perfect excuse to build another weather station.

One decision I had to take when designing the new weather station was how to send data from the nice housing I built for it in the garden to my home server in Barcelona. I needed some kind of internet connection in the house but that’s something I will talk about in another post. I could have used a RN-XV WIFI module like the one I’m using for the rentalito but it’s expensive and I really wanted something simpler to use.

I had already a couple of Ciseco’s XRF radios and decided to give them a try (they are now selling version 2 of theses radios, I have v1.5 modules). These modules provide an easy way to create a wireless transparent RF serial connection between two nodes, no need to configure anything. They have a better range than Bluetooth, WIFI or Zigbee, since they use a longer wavelength to operate (868 to 915 MHz). Off course they can do a lot more than that. They are based on Texas Instruments’ CC1110, a low-power System-on-Chip and you can write and load your own firmware on them. Ciseco provides a series of closed-source firmwares (they call them “personalities“) for these radios, focused on different sensor inputs. You can find more information in the openmicros.org wiki, there is enough to spend a couple of hours reading but I have to say the wiki is kind of a mess, although they have improved it a lot in the last year or so.

Ciseco XRF wireless RF radio

Ciseco XRF wireless RF radio v1.5

Anyway, out-of-the-box these modules are a transparent RF link and their footprint is compatible with XBee modules, so you can use them with your XBee Explorers, Arduino FIOs,… (well played Ciseco). Like in my previous weather station I decided to use an Arduino FIO as a controller (DC-IN, LiPo battery backed, XBee socket,…) so I just stacked one of these modules on it. Inside the house I prepared the “gateway”: an Arduino Leonardo, with an Ethernet shield and a Wireless Shield with another XRF module. The Ethernet shield connected the Arduino to a TP-LINK WR703N WIFI router loaded with openWRT with a 3G USB stick. The small router provides internet connection to the Arduino and to any other device inside the house via WIFI. The WR703N is a really awesome, small and hackable piece of hardware. But as I have already said, you will have to wait for the whole picture of the connection between the weather station and my home server, I want to focus on the radios and the protocol now.

Now that we have the hardware it’s time to think about the message. Ciseco promotes the use a a light-weigth protocol named, well, Lightweight Local Automation Protocol, or LLAP. You can read all about it in the LLAP Reference Guide in the openmicros.org wiki. The protocol defines two node types: controller and device; a message format formed by a start byte (‘a’), device identification (2 bytes) and a payload (9 bytes); and a communications protocol (address allocation, request/response pairs,…). The different “personalities” provided by Ciseco use this message protocol to report sensor values and they can even be configured remotely this way. But Ciseco also provides an Arduino LLAPSerial library so anyone can easily create LLAP devices using XRF radios or other products from the company that integrate a MUC.

Ciseco LLAP library for Arduino is OK, and it works, but it looks like a draft, something you can use to build upon it. So I decided to do just that. You can checkout my version of the LLAPSerial library for Arduino from Bitbucket. Initially I did a fork of Ciseco version but finally I decided to break the dependency with it because some features I added made it incompatible with the original one, although the protocol is 100% backwards compatible. The differences are summarized in the README file but here you have a quick-view:

  • Removed power management code (this library focuses on LLAP protocol and messaging)
  • Added support to use different Hardware and Software serial ports
  • Provided a unique overloaded sendMessage method that supports sending char/int/float messages
  • Provided a way to broadcast messages (see below) using special device ID ‘..’
  • Defined the “coordinator” node, which will always process all messages, regardless the destination
  • Disallow CHDEVID to coordinator nodes
  • Major renaming and refactoring (sorry)
  • Added doc comments
  • Address negotiation and persistence NEW!!

This sample code shows the use of the library to report data from a DHT22 temperature and humidity sensor using LLAP.

#include <LLAPSerial.h>
#include <DHT22.h>

#define DEVICE_ID "DI"
#define DHT_PIN 2

// DHT22 connections:
// Connect pin 1 (on the left) of the sensor to 3.3V
// Connect pin 2 of the sensor to whatever your DHT_PIN is
// Connect pin 4 (on the right) of the sensor to GROUND
// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor

DHT22 dht(DHT_PIN);
LLAPSerial LLAP(Serial);

void setup() {

   // This should match your radio baud rate

   // This device has a static ID


void loop() {

   static unsigned long lastTime = millis();
   if (millis() - lastTime >= 10000) {

      lastTime = millis();

      DHT22_ERROR_t errorCode = dht.readData();
      if (errorCode == DHT_ERROR_NONE) {
         float t = dht.getTemperatureC();
         float h = dht.getHumidity();
         LLAP.sendMessage("HUM", h, 1);
         LLAP.sendMessage("TMP", t, 1);
      } else {
         LLAP.sendMessage("ERROR", (int) errorCode);



There are some things missing from the library, being the main one the address allocation feature the protocol describes (also missing from Ciseco’s implementation). I will try to add it soon. In the meantime feel free to use any of the two libraries and enjoy the simplicity of LLAP. The last version of the library supports address negotiation between the nodes and the coordinator following the guidelines at LLAP Reference Guide, including address persistence, so a node will keep its address after a reboot.

Counting events with Arduino and PCF8583


I’ve been away for some time. It’s not that I had stopped tinkering, but work and laziness have kept me away from the blog. During these months I have been working mostly on a new weather station (yes, yet another weather station or YAWS). The project was a step forward in a lot of aspects, from carpentry to remote reporting hacking cheap chinese routers and 3G dongles, from new libraries for Arduino to a bidirectional HTTP to MQTT bridge in node.js…

The result has been kind of a fail… mostly due to improper casing, humidity has been a major enemy. Anyway there are quite a few aspects to talk about, so I’ll try to write a series of posts about different hardware and software components involved in the project.

Counting the wind and rain

Two of these components share the same interface: when an event happens a pulse is triggered. The anemometer is a cheap plastic model I bought from todoelectronica.com. It’s specifications state than a 10km/h wind correlates with 4 pulses per second, so it is a simple pulse counter.



The rain gauge is a little more tricky… I bought a wireless rain gauge at ebay but I really didn’t need the wireless feature, it was just a convenient model to hack. The sensor has a seesaw with two small compartments where rain drops fall when passing through the top hole. The seesaw has a small magnet in the middle. When the water weight moves the seesaw down the magnet closes a reed switch triggering the pulse. The water evacuates and the other compartment starts receiving the water.

Wireless Rain Gauge

Wireless Rain Gauge

I hacked the rain sensor disabling all the circuitry and soldering a couple of wires to the reed switch with a load resistor in series. By “disabling the circuitry” I mean cutting the lines to the switch to avoid spurious currents to create noise but leaving the circuit, so it fits nicely inside the sensor.

I decided to use a standard interface for the cables, a 3.5 stereo jack (a mono jack would have been enough but I didn’t have any around). They plug into the main board of the weather station and the signals go to the event counter pins of a couple of PCF8583.

The PCF8583 is very similar to the PCF8563 but it adds several nice features: hardware configurable I2C address with 2 different addresses available (you can throw 2 of these IC in your project without mush hassle), 240 bytes of free RAM, more alarm options and an event counter mode.

According to the datasheet, “The event counter mode is used to count pulses externally applied to the oscillator input (OSCO left open-circuit).”. The count is stored as BCD values in 3 registers. BCD stands for Binary-coded decimal, the most common implementation is to split a byte into 2 groups of 4 bits and use each group to represent a decimal number from 0 to 9. So, for instance, 37 would be encoded as “0011 0111”. Thus, 3 registers or 3 bytes allow a maximum of 1 million events. This IC is very convenient for any project where you want to remove the responsibility of counting events from your microprocessor, and it would have been a very good choice for my smartmeter pulse counter.

To easily access the IC features I have written an Arduino library for the PCF8586. The library is not complete, there are some methods to be implemented yet. But the core time and event counter methods are already there.

To library comes with a simple exemple of usage (I have to add more examples) but to use it as an event counter you will only have to write something like:


// declare an instance of the library for IC at address 0xA0
// (A0 pin connected to ground)
PCF8583 counter(0xA0);

void setup {

    // configure serial link to debug

    // configure PCF8586 to event counter mode and reset counts


void loop {

    // report the events every second



There are a couple of issues to take into consideration.

First: the counter counts double. That’s it: for every pulse it looks like it counts the rising AND the falling edges so you end up with double the counts. I have not been able to find a reason for this, nor even in the datasheet. I have tested it with a controlled set up, cleaning the input with an RC filter and a Schmidt Trigger and it counts exactly double it should…

Second: the maximum external clock frequency in event counter mode is rated to 1MHz. In the real world of my projects noise is an issue with frequencies way bellow that mark, so I only accept sensible values depending on what I’m measure. For instance, the above anemometer sends 4 pulses per second for a 10km/h wind. Fortunately, where I live there are no hurricanes and I have not checked but I doubt that there have ever been gusts of more than 150km/h. That sets a maximum of 60Hz. So in my code I have a check to not trust any value over 60 counts per second.

Final note

Finally, there are some other libraries for the PCF8586, like this one by Ryan Mickfor Netduino or this other one by Eric Debill for Arduino, that are worth checking as a reference.

As always, any comment will be more than welcomed.

It’s nice to be back 🙂

Geiger Counter

My last project is a über-cool Geiger-Muller Counter.

My Geiger Counter

Final box, with a LCD showing the last average CPM every 6 secons and sending the info to the server every minute…

Hardware: Radio Hobby Store Geiger Counter Radiation DIY Kit (second edition)

Some weeks ago I suffered a radioactivity fever, so to speak. I backed the APOC Mini Radiation Detector at Kickstarter and also bought a Geiger Counter Radiation Detector DIY Kit from Radio Hobby Store at Ebay. The former has finished the funding with more than 11 times the pledged amount. The later arrived home some 10 days ago, so I just started playing with it.

Geiger Counter Radiation Detector DIY Kit by Radio Hobby Store

Geiger Counter Radiation Detector DIY Kit by Radio Hobby Store

The kit comes unassembled but every part is through hole and really easy to solder. The kit contains everything to get a basic Geiger Counter except for the SBM-20 Geiger-Muller tube, but those are easy to find at Ebay also and mine arrived just one day after the kit. Once assembled you get a Geiger counter that can be powered with 5V through USB or a terminal block and it beeps and flashes a LED every time a beta o gamma particle enters the tube… But, you also get a VCC and GND pins and an interrupt pin (labelled INT) to power and monitor the counts with your favourite controller. And that’s fun!

To build the kit follow the seller’s advice: take your time and enjoy. It has a bunch of parts but none is too hard to solder. It took me about an hour. The only problem I had was with IPA. IPA, or Isopropyl Alcohol (C3H7OH), is used to clean electronic boards and components. The people at Radio Hobby Store emphasize the use of IPA after soldering to wash any flux or any other potentially problematic residue since the board uses high voltage (~400V). Even thou my board was quite clean after the soldering I followed their advice.

It took me a couple of phone call and a one hour trip to get a bottle of IPA 99% in Barcelona… I’ve read you can find the in some drugstores but the one I was after had a a spray which I found very convenient. So I applied the IPA and is was a mess. I ended up with a cover of metal (?) dirt all over the board… It took me a while to clean it up again and check that nothing was desoldered or disconnected. I don’t know what happened but it was completely unexpected. My guess is that it had something to do with the type of solder I use (lead-free), but again I don’t know.

I need to know more about what IPA is useful for and how it actuates before trying it again. Alcohols might not be that dangerous but playing with chemicals requires a deeper understanding of what you are doing.

Anyway, after this trouble the board worked as it should. I calibrated the blue pot to get around 400V across the Geiger tube, switched it off, unplugged, installed the tube and plugged it again. Then, with an imaginary sound of drums, I switched it on and it began beeping! Yes!

Hardware: The Controller

I prototyped the counter with an Arduino Pro Mini and a Sparkfun Serial Enabled 16×2 LCD which uses simple serial commands to write characters on the LCD. Everything is 5V except for the Arduino but the LCD works with 3V3 TTL signals so no problem.

The first prototype was really easy to assemble. I had it working in less than half an hour, including a first version of the code to count and display the data on the LCD.

Geiger Counter Prototype with an Arduino Pro Mini

Geiger Counter Prototype with an Arduino Pro Mini

The first evolution was to substitute the Arduino Pro Mini with a bare ATmega328P, the very same micro but in a cheaper and bulkier package. I prototyped this second version in a breadboard adding the XBee. Now, the ATmega328P is 5V but the XBee is only 3V3. A TSC295033 linear voltage regulator lowers the voltage to 3V3 to power the radio and a diode and a pull-up resistor protect de DIN line. When the input is LOW the diode is transparent and the DIN pin of the radio sees the LOW and the resistor is dissipating ~10mW. When the input is HIGH (5V) the diode blocks the current and the resistor pulls up the line to 3V3.

I used a Zener in the first prototype and took the picture below before realising my mistake and replaced it with a 1N5819 Schottky diode. The Zener was a BZX85C 3V3, so it was permanently in avalanche breakdown. In fact you can use a Zener but in a different configuration, check Rob Faludi’s post about Xbee level shifting.

Level shifting is a great topic to learn basic stuff about electronics. Whenever there is a question on any forum about this there are tens of different answers. Just give a try to some of them!

The final prototype with a bare ATmega328P

The final prototype with a bare ATmega328P (note the fail: the diode in the DIN line of the XBee has to be a Schottky, not a Zener!)

Eagle schema

Eagle schema

This is the first project where I use this level shifting technique. I had used the simple resistor divider in other projects before (like the Rentalito) but the resistors slow down the signal and can be a problem when using higher baud rates. Also, my first idea was to use the XBee internal pull-ups for level shifting instead of an external one but finally I opted for the second option because the 30K pull-up was too high and resulted in a less than 3V HIGH value in the DIN input. A 1K2 external resistor solved this problem and removed the dependency on configuration.

Finally I moved everything to a stripboard. To design the stripboard I used VeeCAD, a stripboard editor, and it really helped me. There was little room inside the box and my first design was too big. It would have been a nightmare to erase and redraw everything several times in paper but in the computer everything was simpler and I could play with different designs until I found the one that was both clean and small. The free version is good enough to design anything on a stripboard but the commercial version (26.26 USD) adds some goodies that can make the difference: color, net tracing and the ability to place elements diagonally.

But, I made a mistake. I crossed the RX and TX lines between the controller and the FTDI header and I didn’t realize it until I tried to reprogram the chip. Anyway it was easy to fix and in the layout below, generated with VeeCAD, this mistake has been fixed.

Stripboard layout (powered by VeeCAD)

Stripboard layout (capture from VeeCAD). The RX and TX lines between the ATmega328P and the FTDI header are right

The real thing, note the fix for the RX/TX mistake:

The real thing

The controler board with the ATmega328P and the XBee. Note the green cable I used to fix the RX/TX error.

Hardware: The LCD

Sparkfun’s Serial LCD is really easy to use, but I wanted to give a chance to some cheap LCDs and I2C serial boards I had recently bought at Ebay. I had already done some tests the night I received them. The seller provides a library and some sample code but I was not able to make it work and I quitted to go to bed.

So this was a second chance to make the think work. The boards I had bought to drive the LCD were I2C serial interface boards (just search for “IIC/I2C/TWI/SP​​I Serial Interface Board Module” at Ebay). These boards use a PCF8574, an 8 bit I/O expander with I2C interface, basically it lets you drive the LCD with just 2 wires for power and ground and 2 more for data (SDA) and clock (SCL).

IIC/I2C/TWI/SP​​I Serial Interface Board Module

IIC/I2C/TWI/SP​​I Serial Interface Board Module bought at Ebay. The solder job could have been better…

None of the libraries for Arduino I tested worked with the board. After googling a bit I found a thread on the Arduino Forum where a user (Riva, thanks!) had found out that the connections were not what the library he was using expected. So I grabbed the tester, put it in continuity mode, and checked what connections led where. The library I wanted to use (NewLiquidCrystal) has a constructor where you can explicitly define the pins so I just instantiated my LCD object with the right pin assignments and voilà.

The initialization code for the LCD is as follows:

// Thanks to Riva for pointing out the wrong pin order
// http://arduino.cc/forum/index.php?topic=164722.0
// 0 -> RS
// 1 -> RW
// 2 -> EN
// 3 -> LED
// 4 -> D4
// 5 -> D5
// 6 -> D6
// 7 -> D7
// Constructor with backlight control
// LiquidCrystal_I2C(uint8_t lcd_Addr, uint8_t En, uint8_t Rw, uint8_t Rs,.
//                  uint8_t d4, uint8_t d5, uint8_t d6, uint8_t d7,
//                  uint8_t backlighPin, t_backlighPol pol);

LiquidCrystal_I2C lcd(0x20, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);

Hardware: The Box

I happened to have the perfect box for this project. It is transparent, elegant and everything fits inside like if it was designed for the project. The only trouble was finding a way to place the cables so they do not cover the tube or the radio antennae.

Everything fits nicely in the box

Everything fits nicely in the box


The code is very simple. There are only a couple of things worth noticing: the LCD connection mentioned before and the ring buffer implemented to store partial readings. The reason for the ring buffer is that I wanted to update the display more often than once every minute with a “moving sum” of counts.

Basically there are 10 cells that store partial counts. Every 6 seconds the code stores the current pulses count value in a cell of the ring, overwriting the previous value. So the sum of the cells values is the count value for the last 60 seconds. To avoid having to sum all the cells on every update, the sum gets updated before pushing the new value to the cell by subtracting the current value for that cell and adding the new one.

// calculate the moving sum of counts
cpm = cpm - ring[pointer] + pulses;

// store the current period value
ring[pointer] = pulses;

// reset the interrupt counter
pulses = 0;

// move the pointer to the next position in the ring
pointer = (pointer + 1) % UPDATES_PER_PERIOD;

That’s it. There isn’t much more to say. As always, the code, schematics and other documentation, are available at github.

One last thing about the software: I have started using Ino Toolkit for this project. If you have it installed you can run “ino build” from the code folder to get the binaries. I don’t like the Arduino IDE: it is very feature limited, the editor is clumsy and the whole thing is too heavy. I’ve always used different command line tools like ed.am Arduino Makefile. My first impressions are good, it has better library discovery capabilities but I missed the “make size” command to know how much free space left you have to code more features…

Testing it!

I was going to add some theory explaining the different types of radiation, how a Geiger-Muller tube works and some reference levels but there are plenty of pages on the internet about the subject and I will not add anything new. Instead I can recommend you to read this tutorial that the people from Cooking Hacks have put together for their Arduino geiger counter shield.

There are a number of natural radioactivity sources. The first of them being the background radiation which you will always get. With my detector this background radiation averages 26 CPM over long periods (more than one day). Then you have some commonly available sources like smoke alarms, some paint used in pottery, luminous displays from old watches or compasses, gas mantles or anything with potassium, like some low-sodium kitchen salt or even bananas.


Low sodium salt (66% of potassium salt)

This low-sodium salt is the easiest to find in Barcelona (apart from bananas) so I just went to the supermarket and bought a tin of LoSalt “The Original” (sic). Then I poured some salt on a self-sealing bag and put it over the Geiger-Muller tube. In any given sample, every 8547 atoms of potassium there is one isotope of 40K, which is radioactive. Potassium 40 is a very interesting isotope, it represents the largest source of radioactivity in human body and has a half-life of 1,250·109 years (if you have a sample of 40K, after one thousand million years only half of its atoms will have gone through a radioactive decay). The counts with the potassium salt bag near the tube raised to almost 139 CPM on average over a 10 minutes record. That is more than 5 times the background noise…

The Geiger counter with a sample of LoSalt

The Geiger counter with a sample of LoSalt. The display reads 139 CPM.

To get a higher count sample I went to Ebay and bought one Thorium Latern Mantle or Gas Mantle. Funny enough, even though these mantles were pretty common here 20 years ago I had to go to an USA supplier to get one. These mantles are impregnated with thorium dioxide to produce a brighter white light. They were retired, mainly because the safety concerns for people involved in the manufacture. Thorium (232Th) is a radioactive element, part of the Thorium decay chain which undergoes several alpha and beta decays until it stabilizes as Lead (208Pb). The test with the Thorium Mantle was impressive. The seller said the set of mantles he had read between 1100 and 2100 CPM. Mine read an average of 1662 CPM over a 5 minutes test but wrapping it around the tube I got up to 1903 CPM.

The Geiger counter with a Thorium Gas Mantle covering it

The Geiger counter with a Thorium Gas Mantle covering it

Thorium gas mantle reading

In the picture the display reads 1823 CPM, it peaked 1903 CPM.

I repeated the tests isolating the gas mantle (it was already inside a plastic bag) from the counter with a paper first and then with a couple of layers of aluminium foil. The experiment set up was not quite right because the readings with the paper were about a 33% lower than without it and that makes no sense since the paper would have blocked only alpha radiation and the tube is sensitive to beta and gamma. Nevertheless I think it is worth it to post here the results. In the graphic below, the first bump is the Potassium salt sample, the second is the thorium gas mantle only with the plastic cover, then with the paper and then with the aluminium foil.

The first bump is due to a sample of KCl, the second, third and forth bumps are a Thorium Gas Mantle with plastic, paper and aluminium foil shielding.

Of course, the sensor is also reporting to my home MQTT network and then the readings are sent to Cosm Xively in almost real-time, here you have the last 24 hours of readings:

The Rentalito

“Say Hello to The Rentalito!”

That was the first message The Rentalito displayed almost 2 years ago. The Rentalito means something like “small rental monitoring thingy” (free translation from “rental” and “ito”, which is the suffix for “small” in Spanish). It was born to display the rentals in a VOD project my team was working at that time. The Rentalito displayed total rentals, rentals by day and it beeped every time a new rental showed up in the database displaying the movie that was just rented.

The Rentalito at Work

In the beginning it was funny and kind of a party every time it beeped. The time between beeps was quite spaced but it was just the beginning, you know. But as the project went on and the rentals didn’t reach the required pace my team was moved to other projects and shortly after I left the company and The Rentalito came back home with me.

The Rentalito uses two 32×16 RG Dot Matrix displays by SureElectronics. They cost about $32 each on the official store, I bought it on ebay. They use a Holtek HT1632C driver and there are a bunch of libraries (in github, in google code) and examples on using these displays with Arduino. I grabbed one that suited my needs (it works, it’s easy to use, and has scrolling text functionality) and added a couple of functionalities. You can check it out here.

The first version of The Rentalito was based on an Arduino UNO with an Ethernet shield and the display was wired with jumper wires to the shield headers. Quite messy. So every thing was hidden from view with a cardboard (!!) box with a sticker on it designed by the team designer (yeah, it’s a VHS video tape). Everything was held together with a sheet of plywood, some screws and spacers.

The code was not better looking but it worked. The Arduino requested the data to a PHP web application that was running on my laptop, it queried the production database to get the latest data and built a message in a proprietary format that was sent back to the Arduino, there it got parsed and displayed. The server application used a SQLite database to store aggregated data and custom messages that could be scheduled based on date and time (like “Good morning” before 10am or “Today is Einar’s birthday!!” when it was Einar’s birthday). The response could contain more than one message. Each message had title and body (or just body for a full screen message) and some control codes (text color, beep,…). The system worked fine but it was not very flexible.

The Rentalito goes WIFI

In its second life The Rentalito went WIFI. Using a Roving Networks RN-XV module and a custom Arduino shield that had a male header to plug the cable from the display. Tidier.

Rentalito Schematics

Rentalito Schematics

Software side I replaced the Ethernet library with WiFlyHQ by harlequin-tech. The library is really good, easy to use and very configurable but it doesn’t implement the Ethernet Client API so it is not a drop-in replacement for the stock Ethernet library.

The Rentalito goes MQTT!!

The last evolution of The Rentalito has been integrating into my home network as a MQTT client using excellent Nick O’Leary’s PubSubClient library for Arduino. But to make it work  I had to switch to a WIFI library that uses the Ethernet Client API. After testing some existing libraries I chose Sparkfun’s Wifly Shield library, basically because it worked.

Although there are several points for improvement in the code (mainly the ht1632c library) the approach is much more flexible now. The main problem is some ugly incompatibility between the ht1632c library and the WiFly library which causes the connection to hang sometimes when a new message arrives while refreshing the display. It’s probably due to the fact that I am using SoftwareSerial library instead of hardware serial. Anyway, if not using scrolling messages the display works for hours without problems and even if there is a problem there is code to reconnect and keep going. The code is available on github.

On the outside the new version has also seen some changes. I finally got rid of the wooden sheet and then cardboard box replacing them by two sheets of methacrylate which make it look cooler (my opinion at least) and give it  some support to stand over a flat surface.

The Rentalito perspective

The Rentalito perspective

The Rentalito close view

The Rentalito close view

The Rentalito displaying the current power consumption

The Rentalito displaying the current power consumption

The Rentalito has suffered different metamorphosis for the past months and I am sure this won’t be it’s last reincarnation.

Decoding 433MHz RF data from wireless switches

[Update 2013-03-01] I have added more documentation on the codes these remotes use in a different post.

I’m starting to move towards not only gathering information but also acting. My first project in this subject will be controlling some lights and the house heaters. So last week I visited the urban market of “Els Encants” in Barcelona and bought some very cheap wireless outlets.

Two different remotes

I bought two sets of three wall plugs, each set with it’s own remote. They all transmit in the 433MHz frequency and I already had a set of transmitter and receiver for that frequency so as soon as I had some time I started trying to intercept and reproduce the codes the remotes were sending.

Sample outlets from each set plus remotes

Sample outlets from each set plus remotes

In the image above you can see an outlet and the remote for each of the sets. The left one is branded “Noru” and each outlet is rated 3kW (good for the heaters) and it features auto switch off time (1, 2, 4 or 8 hours). The remote can control a maximum of 3 outlets and apparently it is programmable, since you first have to sync the outlets with the remote.

The right one is branded “Avidsen”, also 433Mhz but rated 1000W, just below the consumption of my house electrical heaters, but good to control lights and other appliances. It’s got the very common dip switch to sync the remote and up to five outlets. There are 32 different channels available. So if your lights switch on and off randomly maybe you neighbour is using the same channel you are, then you better change the channel.

Available libraries for Arduino

I started reading documentation about the protocol these devices use and found out there is some very useful information out there. In fact there are even a couple of libraries for Arduino. The first one is called RemoteSwitch and it is a little old, it has not been ported to Arduino 1.0 but if you are like me you will keep a copy of Arduino 0023 just for this kind of situations.

The second library is called RCSwitch and I have to say it is a neat piece of code. It has been ported to the Raspberry Pi, although the port is not as updated as the original Arduino library.

My first tests with the RemoteSwitch library were encouraging. The Show_received_code sketch dumped the codes for the Avidsen remote one by one. I though: if it can decode it, it should be able to recreate it. And it worked from scratch. Good!

But by then I knew I wanted to use the newer library. There were several reason for this: it is being actively developed, it supports more protocols, the code is much more elegant and object oriented and it has a port to RPi, which I plan to use as a central gateway soon. So I checked which one of the RCSwitch protocols matched the one I had successfully used with RemoteSwitch and started doing some more tests…

Slightly different protocol

Here was when things started to get complicated. The thing did not work. So I spent a couple of hours studying the code for both libraries, decoding the codes the RemoteSwitch library had dumped before and trying to find the difference. Until I found it: RCSwitch.cpp, line 239, that ‘0’ should be a ‘1’… and everything started working again. Very good! I started a thread in the library forum to find out whether this is a bug or a slightly different protocol.

Index: RCSwitch.cpp
--- RCSwitch.cpp	(revision 219)
+++ RCSwitch.cpp	(working copy)
@@ -284,7 +284,7 @@
         if (sGroup[i] == '0') {
             sDipSwitches[j++] = 'F';
         } else {
-            sDipSwitches[j++] = '0';
+            sDipSwitches[j++] = '1';

By the way, the protocol of these things is pretty interesting. It’s worth a look at Sui’s post to get an overview of the implementation. The tri-bit concept is really awkward.

Using the Bus Pirate and OLS Logic Analyser

Then I moved to the other set of outlets. These are rated 3000W so I plan to use them to control my house heaters, which is the main reason for all this work. I followed the same steps, starting with getting the codes with the Show_received_code sketch. But weird enough the library was only able to decode some of the button presses… Only the SET button for outlet #1, the ON and OFF buttons for outlet #2, the ALL OFF button or the 2, 4 and 8H timeout buttons seemed to work.

This time it was going to be harder, since I didn’t even have all the codes. Well, a good opportunity to use my Bus Pirate!

Bus Pirate to the rescue!

Bus Pirate to the rescue!

So I plugged the RF receiver to the Bus Pirate and launched the OLS Logic Analyser to capture the signal from the remote.

You don’t have to configure anything to use the Bus Pirate as a (low speed) logic analyser. But since I wanted to power the radio receiver with the BP I had to enable the Power Supply mode. To do so you have to open a terminal session, type ‘?’ to get a prompt, select one of the modes that allow enabling the power supply typing ‘m’ and selecting the mode (like UART, for instance) and then type ‘W’ (uppercase to enable, lowercase to disable). Then you can close the session and it will keep the power on the 5V and 3V3 lines as long as it is plugged to the computer. Mind you have to free the port so the logic analyser software can use it. I had problems doing it with screen or minicom, but it worked great with picocom.

After some tests with the Avidsen remote (I knew what the codes were so I could compare the signal output with the actual code) I started getting the signals for each and every button in the Noru remote.

The image below shows the signal for the ON button for the outlet #1.

Signal for the #1 ON button of the Noru remote

Signal for the #1 ON button of the Noru remote

Now, since the RemoteSwitch library was able to decode some of the signals, the protocol could not be that different. So I started to decode manually all the signals applying the same protocol. The signal is a series of 12 tri-bits plus a sync-bit. For the Avidsen-like remotes there are 3 different tri-bit values (logically), they are called 0, 1 and F, for “floating”. Each tri-bit has a pulses shape. The following tables describes the pulses:

Tri-bit Pulses
0 short high + long low + short high + long low
1 long high + short low + long high + short low
F short high + long low + long high + short low

The long pulses are about 3 times the length of the sort ones. The overall period is a characteristic of each remote. There is also a trailing high pulse followed by a long low which is called “sync bit”.

A fourth tri-bit?

Decoding the signals from the Noru remote I found out that there was a fourth tri-bit value (well maybe I should call them tetra-bits now). In fact it is obvious since there is a forth option for an alternate sequence of 4 highs and lows. I’ve named the new tetra-bit X (for unknown, but also after my name :P). The full table for the Noru remotes is:

Tretra-bit Pulses
0 short high + long low + short high + long low
1 long high + short low + long high + short low
F short high + long low + long high + short low
X long high + short low + short high + long low

Now the previous image for the ON#1 button can be decoded as 1F000001FFX0S. With a small patch I could make this work with the RCSwitch library. The library cannot create the code but you can feed it to the sendTriState method to generate the signal.

Index: RCSwitch.h
--- RCSwitch.h	(revision 219)
+++ RCSwitch.h	(working copy)
@@ -106,6 +106,7 @@
     void sendT0();
     void sendT1();
     void sendTF();
+    void sendTX();
     void send0();
     void send1();
     void sendSync();
Index: RCSwitch.cpp
--- RCSwitch.cpp	(revision 219)
+++ RCSwitch.cpp	(working copy)
@@ -441,6 +441,9 @@
         case '1':
+        case 'X':
+          this->sendTX();
+        break;
@@ -561,6 +564,16 @@
 void RCSwitch::sendTF() {
+ * Sends a Tri-State "X" Bit
+ *            ___   _
+ * Waveform: |   |_| |___
+ */
+void RCSwitch::sendTX() {
+  this->transmit(3,1);
+  this->transmit(1,3);


And this is a sample code for Arduino that switches on and off outlet #1 every 2 seconds.

#include <RCSwitch.h>

RCSwitch mySwitch = RCSwitch();

void setup() {


  // Transmitter is connected to Arduino Pin #11

  // Optional set pulse length.

  // Optional set protocol (default is 1, will work for most outlets)

  // Optional set number of transmission repetitions.


void loop() {

Again, comments are more than welcome!