čtvrtek 26. března 2015

Miniature GM detector, part I

First thing first. I tested the GM tubes from yesterday, and the results are more or less as expected. The huge tube, SI-22G, is really sensitive to the background, and it was nice to have it sitting on my desk and clicking. The STS-5, that one in the middle, was more or less on par with the SBM-20 I am using for my detector. The tiny one, SBM-21 does not seem to care about background much. I did not have any active source at hand, but I believe the results will be different when actually measuring something hot. The tiny tube is simply too small, compared to the monstrous SI-22G, and the chances that a particle will hit such a small target are simply... small.
I started to work on the miniature version of the GM detector, and I cloned the HV supply from my very first design, using the same parts, and duplicating the capacitors to achieve similar 
capacity as the original design (original caps are 18nF, these small blue ones are 10nF only). The results are positive - without load, the HV supply draws less than 0.5mA from 9V battery, and 0.25mA from 4.2LiPol 18650 accumulator. I am not sure what was the trick, though. The basic schematic comes from the Geiger Counter Circuits, the second circuit. Picture above is the component side, the picture on the left is the bottom side. I used SMD parts for pretty much all I could. Transistors are SMBT3904, 3906 and SMBTA42. I believe the transistor selection is vital, the SMBT39xx have relatively high hfe. Inductor uses cca 100-200 turns on ferrite core (hand wound). I don't remember what is exact inductivity, but it was pretty high when I measured it before, around or over 50mH. My impression is that bigger is better here. The ferrite core bears marks "SEM TM12". It's either coming from Pollin (part of the mixed inductor sale), or from local shop. Pollin is more likely.
The power supply seems to be relatively 'hard' - measuring the voltage with common 10MOhm multimeter shows 270V, while my previous constructions usually did not get over 150V. I still did not add the GM tube and clicker, that's left for tomorrow, or more likely after my vacation.

středa 25. března 2015

GitHub! (and fixing yet another old LCD)

Let me start with a picture today again. I swear I am not making it up!
This morning, my wife attempted to start her PC, and after a while, she said "Well, I don't want to sound stupid - but my monitor died." Let me remember that few days ago, I fixed two old FSC P19-2 LCD monitors. My wife uses the third one - and obviously, its time has come. I quickly swapped my wife's monitor for the one I fixed already, and went to work.
After arriving hope, I opened the monitor and discovered another failed Capxon, this time 100uF/25V. The top was bulged slightly, but as you can see on the picture, it was pretty much done. Luckily, I found some Samxon KM capacitors that seem to do the trick for the moment, and I already ordered some Rubycon and Panasonic ones.

The second picture shows the GM tubes that arrived from Bulgary recently. The middle one is STS-5, an equivalent of SBM-20. That lovely little tube is SBM-21 I want to use for pocket GM I could carry with me on vacation to Krkonose. The big one is SI-22G to be used for background measurement.
Last thing, the one that took me most of my evening and annoyed and frustrated me almost to death. As you might know, Google will shut down Google Code and suggests to migrate to GitHub. I am not going to rant here about Git - I just don't like it, I find it confusing and overly complicated for my purposes, and I am worried I'll hit the wall using it. But... well, that's the way it is. I had to manually import my Google Code repositories, as the default import didn't work the way I needed, and I already managed to mess the repository by a single click to such a degree I almost needed to import it from Google code again... I'll give it a try and see if I shall stay with it, or find another SVN service. Anyway, a hint for all who need to use Git - don't waste your time, and go and get TortoiseGit. It makes the whole process of using Git a bit less painful.

úterý 24. března 2015

How much solar power II

I realized I did not post any pictures recently. In order to keep the blog more entertaining, this is my evening creation. I know, it's nothing, but at least a picture!
It's Arduino Uno with Ethernet shield (I bought two of them years ago and used them just a few times for testing, I usually use ENC28J60). I added two power 5.6Ohm resistors in series as a dummy load, and I hacked together a few demos to post the results of the solar panel performance on plot.ly. The graph shows voltage and wattage, the time is shown as number seconds after this evening. Not the best scaling, but it serves the purpose of giving me a better picture of what's going on, and I can monitor the results in realtime from work.
As for today's solar panel performance results - they're both promising and disappointing. After I moved the panel a little to face the morning sun, the wattage jumped to 3.73W. That was at 9:28 before I went to work. The power peaked at cca 4.5W, and changed with the clouds covering the Sun and disappearing again. The last usable reading arrived before 3PM, and then the power begun to decline. A rough guess is I was able to generate some 20Wh. It's not bad, although I'd expect the power to peak higher - those are three 5W panels! However, the position isn't optimal, and especially in winter, the building at the opposite side of the yard casts a shadow on our balcony in the afternoon, that's probably that sharp decline of power at 3PM.
I found some info on proper tilting the panels, and mine are obviously not optimally tilted. For bigger panels I plan, I'll need to come with better way to tilt them, and being able to adjust it over the year. Ideally, they should also trace the Sun, but that would be too complicated.
New goodies arrived - the GM tubes from Bulgary! Pictures tomorrow.

pondělí 23. března 2015

How much solar power?

The problem with my solar panels and experiments is that I have no clue how much power I will be able to generate. Theoretically, I should get 15W on ideal day, with panels properly set. I would expect much less later in the afternoon on a winter day, but so far, I am getting something like a few mW only. I can assume that part of the problem are less than ideal light conditions, not really optimal panels angle, and the fact I am at work during the day, thus all I can observe are results on late afternoon.
To overcome at least the last problem, I hacked together a quick measurement unit - just one of the RF24 nodes I have laying around. The only thing the modul does is measuring the voltage of the panel (bridged with 470 Ohm resistor), and report it to the RasPi that takes care about logging it into file. That way, I should see if the panels are worth anything.
That's pretty much all I've done today, I am afraid.
I received a nice box of goodies, I did not open it but I assume it's those old fans and heatsinks. I overdid it this time for sure, and I will end up with something like 20kg of Alu heatsinks. I am planning to use some of them for LED lights, and I wasn't careful when bidding on eBay - oh well, I can still sell them :)

neděle 22. března 2015

No solar fun on this rainy day

Lazy Sunday here. I slept long, really long. My wife's bed is always so warm when she leaves it that I cannot resist to sneak under her blanket, and this time I fell asleep and woke up at 10AM or even later!
The Sunday wasn't only lazy, but also rainy and dark, not really the day you need when you're playing with solar panels. The ones installed on the balcony generated just a few milliwatts, not worth doing anything with it. I used the LTC3525 I received yesterday, and after a few experiments with coils, I made it work. The mistake was to use the small SMD coil I had at hand, but using bigger, 47uH one helped. The whole setup consists of the 2V solar cell, Schottky diode, 22F goldcap and the LTC chip. Unfortunately the goldcap was drained to 0.7V so it took some time for it to get charged. The power generated by the solar cell on this rainy afternoon was barely able to keep the LTC running without any load, but attaching an Arduino to it was definitely pushing it over the limit, and the voltage begun to drop steadily, mV by mV. To be honest, the Arduino I attached to it wasn't low power at all, it uses LP2981 LDO with something like 100uA of quiescent current, and red power LED with cca 1mA consumption, so I am not that surprised. Let's redo the test with fully charged goldcap, and one of the low power nodes I have.
I modded the meteo node a little. The DHT22 and BMP180 sensors are now powered from Arduino pin, thus I can control their power. The program was changed to not enable the sensors for battery (goldcap) voltages under 3.3V, but the program still needs some tweaking.
While tidying up my desk, I found the 24x2 LCD I bought recently. I had the idea of converting it to a Matrix Orbital compatible display that could be used with Winamp, thus I quickly hacked Arduino to it - just to find out that there's no working plugin! I found "LCDPlugin", but that one is pretty old, and reports that the COM port used for display cannot be accessed. It does work sometimes, but the chances of it working are around 10%. The other plugin is "LCD Smartie", but I don't like the idea of having that program running all the time. As Winamp seems to be dead (the official Winamp page didn't change for years, and just promises something new), I assume it's dead and chances of finding working LCD plugin are close to zero... well, I wonder if there are other players capable of all that Winamp could do, with LCD support. I tried foobar before, but I wasn't impressed at all.

sobota 21. března 2015

Solar panel installation

Not much done today, and no picture unfortunately for reasons explained below.
I was thinking about the best way to put the three small solar panels on my balcony. There were some options, and I decided to let the panels hang on the outer side of railings. I am not sure if that's 'kosher', as the local landlord seems to complain about things like satellite dishes - we'll see. After all, this is the land of alternative energy, solar panels are everywhere, so why not on my balcony! I had to rush to the shop to get some nuts and bolts, and I got cheese and anchovy as well while I was there.
I wired the three panels in parallel. I am still not sure if that's smart, but I'll see, and rewiring them shouldn't be that complicated if necessary. The problem is that those panels are 9V ones, which is sort of a strange voltage for common SLA accumulators. I have both 6V and 12V ones.
When I finished, and put the panels on the balcony, it was already dark, and raining, thus no pictures today.
The meteo node (powered from solar/goldcap combo) died at 4AM, more or less as I expected. The latest reported voltage was 2.71V, but the values from the DHT22 sensor were obviously wrong, and I think I should stop trusting the values much earlier. Let's declare the minimal acceptable voltage as 2.9V. At this level, the voltage begun to drop quickly, and the humidity reported by DHT22 went to the roof. I assume that the sensor simply went to weeds, and consumed all the power it could get before RF24 module gave up :)
I received the long expected LTC3525 chips today - I'll give them a try tomorrow, and also will try pairing it with that 22F goldcap, and see how long a node will run off it!

pátek 20. března 2015

Fixing old LCD monitors - Fujitsu Siemens P19-2

I realized I'll need a secondary LCD monitor for my vacation. I had two FSC P19-2 LCD monitors in my basement, as I was planning on fixing them one day, and the day arrived :) Those monitors were really a high end ones when I bought them (okay, high end consumer ones), sporting PVA panel and pretty good speed and size. They're 1280x1024, 19 inches.
The first one did not start properly, and if it did start, it switched off itself soon again. It dies last year, so I still remembered what was wrong with it. The second one was sitting in the basement for a bit longer, and I just barely recall the backlight died, although I am not completely sure. Anyway, after watching Dave Jones' video on fixing the LCD monitors, I felt confident I'll be able to fix at least one.
Opening it isn't that difficult. A nice guide is on Diit, however after figuring out that the two important screws are hidden under the white rubber plugs, it did not take more than a few minutes. Just demount the monitor stand first (four screws), then the two under the white rubber plugs, and then gently pry the back cover apart. The electronic is hidden under the metal sheet held by three screws around, two screws near the power socket, and the four hexagonal nuts (or how they are called?) of the DVI and VGA connector. Then slide the metal cover off the holders, and that's it.
The source of the problem can be easily spotted - see that green capacitor on the left side of the picture above, close to the heatsink? It's bulged - not much, but it is. More detailed picture on the left. All I needed to do is replacing it with similar, but working capacitor. I didn't have any new one at hand, thus I used an older capacitor I recovered from an old Pentium mainboard - and, well, that was all. After putting the LCD together again, it works, at least for now. The original bulged cap showed no capacity at all!
By the way - I used the same method for fixing our late satellite Topfield receiver. Again, replacing the bulged cap with an old one recovered from old mainboard was sufficient. If you happen to have some old mainboard from the era before those capacitor problems, don't throw them away, keep the caps! And the coils, and maybe some other stuff - heatsinks, PS/2 connectors, resettable fuses...
The second LCD (again, P19-2) was a mystery. It worked when I tried it today, although I am sure it didn't work before. The cap in the power supply that I expected to be bulged was okay. I replaced it just to be sure, and also replaced another, smaller cap nearby that looked bulged, but I did not have adequate low ESR replacement, so I'll order some and will fix it once for all.
That's pretty much for today - oh wait, three small things:
 - the pre-WW2 vase with uranium-oxide paint arrived today. It looks nice, and is not as hot as I expected, showing something around 2000CPM (1mR/h). However, because of bigger active areas, there's a measurably increased radioactivity even some 20cm far from the vase.
 - we had partial Sun eclipse here. I watched it for a while, and although it doesn't compare to the total eclipse I saw in 1999, it was still nice.
 - the meteo node powered by a solar cell and 1F goldcap is still up and kicking. I am using RasPi to monitor it, and despite the fact the node isn't power optimized yet, and reports every 8 seconds, it's still at 3.47V (almost midnight here). The voltage drops by 10mV every 3-4 minutes and I expect it to die at around 3-4AM. With some optimizations, I am pretty sure it can make it through the night! (an afterthought - in emergency situations like when the voltage drops to dangerous levels, what about sending the meteo packet less often?)
Last but not least - I'll rework the sensor packet definition to give bigger range of voltages. Maybe one bit flag, specifying either 10mV precision as being used by now, or something like 50mV usable for higher voltages. Actually, that would be backward compatible!

čtvrtek 19. března 2015

Fixing old central, and fixing meteo node

Time flies - I just wanted to finish something, and it's almost midnight.
We had some problems with electricity yesterday. Few weeks ago, the wall socket in the bathroom burned out. Well, not really, but my wife reported strange smell when using the washing machine. It wasn't your typical burning smell, it was more like ironing a perfumed piece of clothing. As a quick hack, I asked my wife to use an extender cord. However, the other circuit did not handle a water kettle and the washing machine at the same time, and breakers went off.
I am using an old central node designed few years ago. The new, Arduino Due based central node I am working on is supposed to replace this old central node.
The old central node has a problem I was aware of, but wasn't able to debug so far. Sometimes, it simply hangs after being powered up, or stutters in the main loop. I noticed that before, but the problem went away when I attached the debugger. This time, it didn't, and first debug output suggested the central node isn't getting the IP address via DHCP. A few tests suggested the MAC address isn't unique, and router refuses to assign new IP. I am still not sure what caused this, probably a router problem. I'll keep an eye on it and if it happens again, I'll generate random MAC on every start or something.
Next thing I worked on this evening was making the RasPi log all the sensor node packets into a file. It was pretty simple, and works fine so far. I want to see what exactly is happening with the meteo node in the evening.
The meteo node was also modified to report the correct voltage of the goldcap that powers it. I assume the sensor are eating too much of juice, and the whole thing will need some optimization. Not a big deal, I was planning on running this from battery anyway, but - well, if it can be solar powered, even better!

středa 18. března 2015

Goldcaps? Goldcaps!

As promised yesterday, some new toys that arrived recently. I got some solar panels - those are 4.5V and 5V rated ones. The 5V one can actually put over 5.6V on a really bright sunlight, which is - after dropping 0.2V of the forward voltage of a Schottky diode - close to the 5.5V rating of the goldcap, so I am using the 4.5V panel. Then, there are two goldcaps, 1F/5.5V and 22F/2.3V, and finally a sealed lead-acid accumulator, 6V/4Ah.
First thing I tried was a few experiments with the goldcaps and solar panels, of course. I just added the BAT54 Schottky diode and used my incadescent lamp to generate some electricity. The voltage went up nicely and I was watching the 22F goldcap charging - sweet! After removing the light, the voltage begun to drop quickly, and it looked like the self discharge of the goldcap is that high that it won't hold the charge for more than just a few minutes!
After looking up more info on web, I realized that a goldcap is really behaving like that - the charge slowly trickles in and it takes some time for it to reach all the parts of the golcap. To prove that, I let the goldcap with attached panel charge all the day on the balcony. It got charged to 1.9V, and after more than a day, the voltage dropped to 1.78V only. Much better!
I used the 5.5V goldcap with the meteo node. It worked over day, but after nightfall, the voltage dropped pretty quickly and the node only worked for a few hours. I need to create a monitoring and logging tool that isn't dependant on my computer working all the time. Hmmm, a good application for RasPI! If nothing else, I know it works with RF24 *evil grin*.
That's all for today, I need to make plans for further steps. One of them will be finding the best way how to put the solar panels (the 9V ones I have) on the balcony, on a direct sunlight, avoiding my wife's flowers and plants, and the sunshades she puts over the flowers on hot days. That's the trickiest thing.

úterý 17. března 2015

Back from vacation

I took a break, partly due to high workload at work, partly due to a short trip to my family. I did enjoy it, and even enjoyed driving that tiny, brand new Ford Fiesta I got from Hertz. That was a nice surprise, I paid for Ka, and got Fiesta.
Last two evenings before the departure (well, not exactly, last two evenings were mostly about packing, planning the trip, getting the Google Maps working on my phone etc etc).. what was I talking about? Oh yes. Last two evenings before the departure were about making the RFM12B work with Due. I finally decided on removing the display, and the freed SPI port is now used for RFM12B. I started porting the library to Due, but that turned out to be pretty complex task, as the library uses various bits and pieces specific for AVR (like EEPROM etc.) and I gave up pretty quickly as I had that feeling of reinventing the wheel. I took the library from Boredomprojects and first tests looked really promising, it could talk to Arduino running the latest version of Jeelib.
Happy about the progress, I tried to send a broadcast message to my already existing devices with RFM12B - and... well, nothing happened. After some debugging, I figured out two things that were wrong:
 - the existing devices use old version of the library. New version adds one byte in the header for destination or source address
 - the new library initializes the RFM12B to a different speed
After fixing those two problems - nothing happened. I tried all I could think of, but the Due running new library with my patches still doesn't talk to the old devices. The packet seems to be correct, the CRC matches, the channel and speed is the same... I gave up for the moment as I had no time to pursue that. I'll debug the init sequence using my good old Saleae clone and see if there are any differences.
In the meantime, I received a whole bunch of new stuff. The most interesting things are some goldcaps, solar panels, LCR meter, RF24 modules with antenna, partly dead MX510 mouse (as a spare part donor for the mouse I am using for years), and other small stuff. I should do an unboxing video one day :)
I did some experiments with the goldcaps, and I'll put together some more info in upcoming days.

sobota 7. března 2015

Barbie bed

I felt like doing something else today, I definitely need a break and think about further updates of the central node. I was asked to build a bed for Barbie and her friend, so here it is. The frame is made of plywood, my wife provided the fabric, and the mattress from soft foam material I found somewhere, it was originally part of keyboard packing or something like that.

I used my old good Proxxon table saw. The saw is fastened to a little plank of wood by four screws, and then the plank is fastened to the table with two clamps. To cut big pieces of plywood more or less rectangular, I made a bigger working are of plywood and some squared timber. It's not perfectly rectangular, and has other problems, but with a bit of effort, the results are at least satisfying.
The frame slides along the saw table, and helps me to make long and straight cuts. Unfortunately, this whole arrangement only allows me to cut plywood not thicker than 5-6mm, but it's still a major help.

I also made another attempt on the high voltage power supply for GM counter. The results are even worse than the previous attempt, and I am wondering why. I ordered some 9.1MOhm SMD resistors, and next attemp will use SMD transistors, the same I used for the very first supply.
Some minor changes were done to the central node code as well, but nothing major. I started to look into the available libraries for RFM12B that could be used with Due. I found one, using SPI port, but I am a bit skeptical about it - plus, of course, I have no free SPI CS pins. However, I am considering getting rid of the display, and if nothing else, I can just convert an existing library to use SW SPI.
Why removing the display? First, I am not sure how useful it will be in final product. It is pretty useful now, but the nRF24L01 modules have quite short range, and even with 250kbps, the signal doesn't make it through walls to the bathroom. To overcome this, I am considering putting the central node to more central location in the appartment, but then the display will be useless. Second, as clearing the screen takes over 100ms, it would greatly impact the response time of the RF24Network, eventually losing packets randomly, and I don't like that idea.

čtvrtek 5. března 2015

Meteo node II

I'm reporting some progress on the meteo node today. It worked more or less on first power on - with the exception of the RF24 not working at all, but the problem was easy to discover - swapped pins MISO and SCK! I don't get how could I make that mistake as I was following the table, and I am sure I counted the pins right. Anyway, after fixing that, all worked just fine.
The node still misses the battery measurement support, but I am going to leave it out until I know what kind of battery I am actually going to use. The voltage divider will depend on if I am going to power it from AA cell, LiIon cell or something else. I ordered some samples of step-up converter from Linear, which could be used, and I am considering those MCP1640 from Farnell (they're still the cheapest), but that needs some testing first.
The high voltage capacitors finally arrived from Austria - sheesh, it took more than a week to get them shipped and delivered, and given the S/H price... I just hope they're any good, or else I ended up with 200 pieces of junk. They're surprisingly small for 1KV 10nF capacitors. Anyway, I'll see if I find some time this weekend to build - yes, you guessed - yet another HV power supply for GM tubes. In fact, I am thinking about putting together the not-so-common components and offer it on eBay for some reasonable price, saving people from hassle of getting bits and pieces here and there. I have a load of MPSA42 transistors, 10nF capacitors, 10mH inductors, fuse holders etc etc.
The lead accu I ordered month ago still did not arrive, and eBay returned me the money. I ordered some goldcaps today, and will do further experiments with them. I'll get two 22F/2.3V ones that could be great if I'll manage to make the step up converters working.

středa 4. března 2015

Meteo node

After that experiment yesterday that helped me to confirm that I can safely use DHT22 for temperature measurement, I started to work on the meteo node. It's not tested (my wife needed some changes on her blog that took me some time to figure out), but it already is getting shape. The white thingy is the DHT22 sensor, the small bluish one is BMP180 module. I found out the module actually had 3.3V LDO so I  had to remove it, that's why you can see some missing components, and the wire on it. I was originally planning on powering the whole thing from 18650 LiIon accu, but I can't find the holders I bought some time ago. CR2032 was the second choice, but that probably won't work for DHT22 as it is specified for 3.3-6V, and according to some into on web, it starts to show erratic behaviour under 3V. I'll try a step up booster and power the thing from one AA battery. I wanted to order some MCP1640 chips, so this is a good time to do so. Farnell has them for nice 41 cents when ordering 10 pieces... just the shipping price is way too high, so I'd better think of some other stuff I need before I make the purchase. Anyway, the CR2032 should do for the moment.
There is a few things that are still missing - the battery voltage measurement, and I should probably switch off the sensors when Arduino is sleeping to conserve power. The DHT22 draws something like 40uA when idle, which is pretty much a lot of power. Now the question is, how to do that? Using a PNP transistor as a high side switch should work, but I am a bit worried of the voltage drop on it. Of course that would not work at all with CR2032 (that's why I did not add this to the node yet). Another option is to power the sensor from the Arduino digital pin. That should be pretty easy, but again, I am not sure about the voltage. The safest would be to use something like 3.5V for Arduino, which should be fine for all other devices, like the NRF24L01, and still give a plenty of headroom for powering the sensors. Time to do some measurement tomorrow!

úterý 3. března 2015

Temperature sensors precision

I was always curious how much can I trust various types of temperature sensors. I loved the TI's TMP100, tiny I2C based sensors, and used them a lot before. In one project, I got a feeling that the sensors are actually lying to me, and I became a bit cautios. I later abandoned them in favor of DS1820 style sensors, and the few remaining TMP100's were resting in the box. As I recently got the DHT22 that also has temperature sensor, I felt like I should really take a look at various sensors and compare their readings. The results are interesting.
First thing first - the contestants are:
  • TMP100 - I2C based sensor from TI in SOT23-6 package
  • DS1820 (and similar ones) - 1-Wire based sensor from Dallas / Maxim
  • DHT22 - sort of one-wire protocol, temperature and humidity, based on AM2302
I already played with all the DS1820 (DS18B20, DS1822 etc.) sensors I have, comparing all of them, and I found out that at least at room temperature, they all report more or less the same temperature, with maximal difference between the lowest and highest value around 0.5°C.

As always, I took Arduino, attached LCD display to it and all three sensors, using sample code from Arduino libraries. I did not see any example for TMP100, but Google suggested the Fork Robotics page, and the example described on that page worked just fine. I do not offer the code for download, it's a big mess, and throwing it together took me about ten minutes anyway.

The results are interesting, and reassuring me I can use any kind of sensor without risking the temperatures being too different compared to any other sensor. In other words, I can use the DHT22 for the meteo node, and trust the temperature. There is no need for an additional DS18xx sensor on that node.

I tweaked the code for the central node a little, nothing important. I am considering a change of the packet definition, making just a single structure that will use anonymous structures and unions to describe any kind of sensor packet. I am still not sure if there are any drawback other than the obvious one (prone to mistake). Just to explain what do I mean:

typedef union {
  SensorPayloadTemperature_t Temp;
  SensorPayloadMeteo_t Meteo;
  struct {
    uint8_t PacketType;
    uint8_t BattLevel;
    uint8_t ___pad[2];
    uint16_t SensorId;
} SensorPayload_t;
This allows me to directly refer to PacketType, BattLevel etc. without 'going into' the Temp structure. Arduino supports this, at least the 1.5.8 version.

pondělí 2. března 2015

Arduino Due rant and debouncing

Mostly ranting today. I wonder who came up with the brilliant idea to name Arduino Due this way. Did they realize that 'due' is regular English word, and googling up 'Arduino Due xxx', where xxx is a description of the problem, or a library name, will point to regular Arduino article that accidentally uses the word 'due'?
Yeah, I can use doublequotes, but I usually forget to do that. What will be the next great name? 'Arduino And'? 'Arduino The'? Or even better, 'Arduino Sex'? (Actually, that leads to interesting results in Google already). I am already pissed off with that misplaced connector problem (as I described few days ago), and I am more and more believing that those Italians should stick with what they do best (ice cream and pizza), and for gossake don't mess with electronics! (Just kidding, I still like Arduino).
Anyway. I spent a few hours adding button support, or better said debouncing, and using the button to switch between different screens on the display. I tried to use regular Bounce2 library, but that does not compile, and I didn't want to mess with the library. The easiest solution was to use my old debouncing code that also supports autorepeat. The code isn't mine, I found it years ago, and works like a treat. Just call this piece of code in regular intervals, like 10ms, and tweak the constants according to how often the code is being called. 
#define DELAY_REPEAT 25
void UpdateButtons (void) {
  static byte id = 0x00;
  static word key_counter = 0;
  byte c;
  c = GetButtons ();
  if (c == 0) {                   // No key pressed
    id = 0;
    key_counter = 0;
  } else if (c != id) {           // New key differs from previous one
    id = c;
    key_counter = 0;
  } else {                        // New key is the same as previous
  if (key_counter == DELAY_DEBOUNCE) {    // Debouncing complete
    Buttons = id;
  } else if (key_counter == DELAY_REPEAT_START) { // Repeated key
    Buttons = id;
    key_counter -= DELAY_REPEAT;
GetButtons() returns what buttons are pressed in form of bitmap. Global variable Buttons contains a bitmap of pressed buttons. When you process particular button, clear the corresponding bit in Buttons. The constants above are fine when calling the function every 10ms.
(I just looked up in my old sources that it's based on algorithm by guy KimmoHop from avrfreaks.org)

I reviewed the CR2032 node and noticed that there's a potential short circuit that might ground the analog input of the battery voltage measurement when wet. I fixed that, and will give it a try overnight. The voltage is 2890mV right now (it has changed a little after I cut the traces that were likely causing the problems, which suggests they actually had some conductance... or not?)

neděle 1. března 2015

Telling the time

A bit lazy day today, spent on eBay and selling some old junk, getting what was already sold ready for shipment, and playing with the Due central node a little. The node now retrieves the time via NTP and sets its local clock, another step towards telling the time to all nodes that are interested. I did some minor changes of the code, added button and photoresistor to the node, and improved the LED support to make them blink smoothly.
The CR2032 node reported battery dead in the morning. I measured the CR2032 cell and found out that the voltage is perfectly fine. That explains what is going on - it must be the air moisture. Either it condenses on the resistors of the voltage divider, or the cheap chinese paper PCB gets soaked and its resistence decreases. I know it's a really cheap PCB and I am not blaming anyone, I bought a pack of fifty for few euros and they so far performed well. Anyway, I'll leave one of them on balcony for a day and see if it will show any measurable resistence.
If the problem is in the air moisture condensing on the resistors of the voltage divider (they're something like 1M5 and 330K if I recall the values correctly), I'll use standard through-hole resistors for the divider, and maybe smaller values. It should not be a problem, I am grounding the lower end of the divider before measurement, thus it should not draw any noticeable current anyway.
Speaking of power consumption - after the node dried up and the reported voltage stabilised at 2920mV, it didn't change a single bit. Did I finally succeed in creating a sensor node that will run off the CR2032 cell for a few months at least? *evil grin*