Back from Embedded World 2015!

I did not update the blog for a few days. I was on Embedded World 2015 in Nuremberg, visited customer in Essen, and then recovering from all that :) All that were business trips, and I can tell you that all of that was exhausting. I took train to Essen and back, and that was refreshing, I really enjoyed that... but still, it's five hours on train.

We spoke to some people on MS booth (not MS directly), and we were given this 16GB USB stick. I originally thought it's a chewing gum or something. The other side says "Internet of Your Things". IoT was a major buzzword this year. Why not.

I also brought a new STM Nucleo board. I don't have it with me, and I don't remember the model number - just guessing it's the F303RE variant. Unfortunately, I didn't realize I could (and should) register for the NFC expansion board.
I did not bring anything from Essen, but we had time to have a lunch in Maredo steakhouse. Yum!
As for the hardware projects, I did a few minor things.
I was about to update the "white" clock with support for buttons to set time, and when looking into the code, I realized I did it already long time ago. It's funny, the clock was sitting on my desk for a few months and waiting for the update.
I received some goodies from China, one of them a boost-buck converter. I hooked it to the solar panels and I can see it works as expected. The panel voltage dropped to something like 2.5V, so it's still far from ideal, but it was pretty cloudy today anyway. The lead accu I ordered almost a month ago still did not arrive, and I can't test the whole setup with it (eBay case opened already).

I played with the sensor nodes a little, and added some indicator LEDs to the central node, just to show if it's alive, and if packets arrive from time to time. I wanted to use PWM, and most of the PWM capable pins are on that odd-placed Arduino connector (pins 8-13). The trick to make the connector compatible with stripe board can be seen on left. Those are originally pins extracted from right-angled pinheader, and they're bent accordingly using pliers.

I am also making another attempt with the CR2032 based node. I placed it outside on a dry place, let it report every minute, and I will monitor the battery voltage again. It started with 2.94V - or actually a bit higher, but the voltage dropped after moving the node to the balcony. Outside temperature is around 4°C, compared to something like 22°C inside, thus some voltage drop was expected. Other nodes are scattered around the home, just to keep the central node busy.

Last but not least, I again put some stuff on eBay. I sorted out the vacuum tubes I purchased some weeks ago, and found some that might sold (like DY-802, 25kV diode that could be used for X-Ray). We'll see.

Arduino Due Central Node, part III

Yesterday and today was mostly related to the central node and example sensor node. I added those two RF24 modules as planned, and immediatelly ran into problems, as they were not able to pick up almost any packets sent by other nodes. I am still not quite sure what was the problem, but adding some filtering capacitors - a lot of them - helped. One thing that really helped me to realize it could be power supply problem was the fact that the reception got much, much worse after attaching that flat cable with display and Ethernet module (ENC28J60). Even when they weren't in active use, they still messed something up. Anyway, now there's a huge cap (1mF or so) under Arduino and each module has its own 33uF tantalum SMD cap. That seems to do the trick.
Another thing that might have caused problems was the DMA mode used for the display. I decided to turn it off in the end, after realizing it doesn't really play well with other devices on the SPI bus. The sources mentioned something like that the DMA can stall other devices. What I noticed was more like the opposite - clearing the screen took 29ms with DMA enabled before other devices were activated, but a few seconds in the main program loop where other devices were talked to!
I changed the sensor node code to be more similar to the sample code I already wrote. Resulting code uses just pure RF24 radio without the RF24Network extension, runs on 250kbps for longer range, and does not use any acks. I might change it in the future after doing some tests. The sensor node also uses EEPROM and simplified identification in form of two characters, like 'T0' for first temperature sensor etc. The packet that temperature sensors send looks like this:

typedef struct PACKED {
  uint8_t PacketType;
  uint8_t BattLevel;
  uint16_t Flags;
  uint16_t SensorId;
  uint16_t Temperature[2];   // Up to two temperatures in tenths of degrees. 
} SensorPayloadTemperature_t;

To recap, I am planning four types of nodes:

• Central node - Arduino Due, has Internet access and serves as a central hub
• Network nodes - support RF24Network (maybe with Mesh extension), typically used for bigger tasks with a lot of communication happening
• Broadcast receivers (consumers) - RF24 radio only, receiving broadcast info from Central node but do not send anything back. Typically clocks etc. Broadcast receivers have no ID
• Sensors - RF24 radio only, sending data to Central node, not receiving anything. Have simple two char ID to distinguish between multiple sensors of one type

 I also spent most of the afternoon by putting stuff on eBay, some old chips I probably won't use, some kits, VFD displays etc. One VFD display was immediatelly sold, and few people already bid on some microcontrollers - good!
Last but not least. After finishing the Friday's entry, I finally had chance to try my new telescope out. It probably needs some adjusting, but I was able to identify that bright planet I was seeing from my window every evening. It's Jupiter, and I can confirm it as I saw its moons - for the first time in my life! It left me in awe, and Jupiter is no more just a word, but something that physically exists for me.

Arduino Due Central Node, part II

I spent most of the yesterday evening despairing and tearing my hair, struggling with the RF24 nodes on Arduino Due. The logic analyzer gave me confusing results, the signals did not make any sense, and of course the node didn't respond, no matter how I tried. Well, in fact it did respond when I touched the MISO pin, but that wasn't the kind of response I hoped for. Those strange signals on logic analyzer turned out to be caused by slow sampling, and all worked fine when I bumped the sampling frequency to max (24MHz). Anyway, I gave up and went to bed, as I was tired and could not think straight.
Yes, you guessed that already - I made a mistake when wiring the thing. The RF24 modules have two pins named CE and CSN. I assumed that CE is SPI chip select, and CSN is something specific to RF24 module. Even when I saw that the RF24 does not respond, I still did not realize that the module is obviously not selected and there's something wrong with chip selects. Well, that will teach me a lesson for next time.
After swapping the pins, all started to work just fine. I quickly tried if I can use any pin as chip select for SPI, but that doesn't work. As I am still planning on attaching RFM12B sender, it will obviously need to be modified for software SPI... oh well, at least I can reuse the code from ENC28J60.
The plan is to have two RF24 modules. One will be running with just a basic RF24 radio stack, withouth ACK, on 250kpbs (for biggest range), with fixed packet size, and its own channel. This will be used for sensor reporting to central node, and for central node to broadcast info.
The second RF24 module will use different channel and will run the whole RF24Network stack. I am not sure what I will use it for, but if nothing else, it will multicast similar info packages, and additionally provide some services, like offering nodes to sign up for mode detailed and extended info etc.
The rest of the evening took me beautifying the code, and I'll check it into SVN. I'll change the sample RF24 node code to use just the basic radio... and hopefully it will solve that strange quick battery discharge problem. By the way - I am not sure if the voltage measurement is actually not the main cause of the problems. The node is soldered together on rather cheap paper-based PCB, and the voltage dividers use pretty high value resistors. It could be that the PCB absorbed some water that decreased the PCB resistance and messed up the whole voltage measurement.

Arduino Due Central Node

I started working on the new central node yesterday. After giving up RasPi as the problems I faced and expected were more than I could stand, I decided to go back to roots. Mega was one option, but I decided to try Due this time. If that won't work, I can still go back to Mega, but so far so good, and I am knocking on wood here.
Anyway, the ILI9341 library for Due works just great, the ENC28J60 network behaves as well, and both work together. I wrote really basic sketch just to test the hardware, called DueCentral.  I plan to move all the diagnostic output to TFT as a first step, and make sure that I can get exact time from network. The node also acts as a web server, maybe I could use it somehow? Like a table of all sensors etc...
Of course, when attempting to slap the stripboard on Arduino, I got pissed off again. I definitely need all the connectors to be available on the stripboard, including the famous one that's shifted by 50mils (pins 8-13). This connector provides some pretty important signals, like 10 for SPI CS, and the rest is available as PWM. Oh well, what should I expect from a board designed in Italy - the guys should stick with making ice cream, and don't mess with electronic.
I wanted to update the GM counter sketch yesterday, but I figured out I don't really know what I expect to be displayed and measured, so let's leave it alone for a few days.

ENC28J60 library, GM counter - part III

Lazy evening today, but what would you expect on Monday. I spent most of the time getting the ENC28J60 library to work on Arduino Due, and I succeeded in the end. One of the problems I met was the fact that Due fed from USB cable wasnt' able to provide enough power to the network chip. That was really strange, as the USB cable was connected to a powered hub, but whatever... after using a barrel jack with 12V, the network started to work. I had to do a few minor changes in the library itself, mostly sorting out of the small incompatibilities, like replacing "sei" with "interrupts" etc. The library is available from SVN, revision 154.
I changed the code for GM counter slightly to update the CPM more frequently, basically guessing the CPM based on 5 second measurement with a running average over 30 seconds, and I changed the display from mR/h to uR/h. The natural background shown is between 5-15 uR/h, which is more or less of what I'd expect. According to web, the natural background in Munich is around 0.8mSv/a, that's 80mR/a. Year has 8766 hour, thus we should expect to measure roughly 10uR/h.

ENC28J60 library, GM counter - part II

I continued with what I was working on yesterday. First task today was to get the SW SPI library working with ENC28J60. I used the old goold Ethercard library by Jeelabs, and the porting went pretty well. I did not care to port it properly, with defines and stuff, I just wanted to verify if it works. It does, despite the fact I am using digitalWrite, and the demo properly displays the web page. I'll polish the library in upcoming days, test it on Due (I used Uno for tests today), and will put it into SVN repository.
I also finished the hardware of the GM counter. Nothing big, just small change of the hardware, and adding Arduino Pro Mini and Nokia display, plus some small changes of the HV power supply. I tried to replicate the other power supply, hoping to get the power consumption under 1mA, but no matter how I tried, it stays around 2.5mA unloaded. I don't get it, the power supply is the same, just the transistors are different, and the capacitors are actually smaller - 6.8nF instead of 18nF. Anyway, the whole thing is not supposed to be switched on for extended period of time, and Arduino and display also consume some power, so there's no need to keep it low... but still. I am really curious what causes this. I found some reasonably prices disc ceramic capacitors on eBay, and those should be smaller than the ones I am using (size-wise), which, combined with a small tube like SBM-21 could make a nice pocket geiger.
I put a very simple software into the Arduino, basically just to find out how it performs, and added basic CPM -> dose calculation based on the SBM-20 datasheet for Ra226. The hottest ore sample I have shows 4 mR/h (on the picture). I bought it as uranocircite, although I guess that there's some torbernite in the sample that's much more active, because the most active part of the sample does not fluoresce, so that's most likely not uranocircite. The reading depends on which value of the CPM -> dose I choose, there are some similar values for Cs137 and Co60, but the final number will be around those 4-5 mR/h.
I have a few ideas for the software, based on these kits. That's definitely something I want to finish next week!

ENC28J60 library, GM counter

As promised and planned, I took better look at the SW SPI modification of the ENC28J60 library. I am not sure I mentioned what library I am using, so here's the link.
Unfortunately, there are two problems:

• the library I originally got was version for regular Arduinos. It took me some time and research to find out there is a branch numbered 1.5.x that is compatible with Arduino Due and Arduino 1.5.x. In fact, I figured this just as I am writing this text. I originally only got a ZIP file what was linked from forum, and just now I realized it's a branch of the library. Anyway, I had problems to compile the thing, and in the end something went wrong and the library stopped work at all. I suspect Arduino, I was changing the versions of the library, and at one moment I had Arduino actually using a library I already deleted!
• the library seems to have a known bug that the communication hangs after a short while. This was supposedly fixed in the branch I didn't have this morning, so I had no chance to test it, and then I moved to another project.

However, my SW SPI modifications actually worked.  The problem I was facing yesterday was just a minor bug in SPI read. The SPI clock goes high, then the data from slave can be read, and then the SPI clock goes low again. After fixing this, Due communicated with network... until the library bug caused it to hang.

I was fed up with that, and moved to the GM counter project. I used slightly different HV power supply for this variant, and it wasn't a good idea. The power supply is safer, sort of, because the output voltage bleeds to zero quickly when I remove the battery. The previous power supply kept the output capacitor charged, and despite it's just something like 10nF, those 450V made a nice spark when I shorted it with a screwdriver! The new power supply drops the voltage to zero within a second or so. Another problem with this new one is the power consumption - unloaded, it draws around 5mA from 5V power supply. The old one, with some tweaking, draws less than 500uA. I am considering to change the new power supply to the old one. See this page. The very first one is the "new" one, second is the "old" one. The second is simpler and better, and given the fact I power it from 4.2 LiIon, there's no need to stick with the new design.
I also found out that when it comes to inductance, bigger is better. The guy recommends 10mH, but I am getting the best performance with an inductance so big I even cannot measure it. The second best is my home wound pot core inductor with something like 80mH. Less inductance means bigger power consumption.

I also received some small toroid cores and I tried to wind my own inductor in an attempt to make the 10mH reference one as being used by the "old" HV power supply. I found nice video about winding toroids, and tried it myself. It's a good idea, unfortunately my wire was thinner, and curled all the time. It took me a lot of time to straighten the curls every turn, and in the end some curls bent, and the wire broke after some 30-40 turns out of 100 planned turns. The enamel on the wire was pretty worn out at some spots, and I wouldn't really want to use the resulting coil in a mission critical application. However, with thicker wire, more patience and after finding a way to straighten the wire so it stays so, I can make my own inductors!

The fastest way to high inductances turned out to be a combination of pot core with plastic holder, and an electric drill. In no time, I had a pot core with few hundreds of turns.