Wednesday, October 19, 2016

After a Long Testing Period, Moving Forward With My Temperature Sensor

A while back I came up with a battery operated temperature sensor that sent its data over my XBee network <link>. This little device has been sitting beside my bed for a long time now and works well. It has had it troubles over the months that I had to fix, but that was the point: make sure it works before moving it into a bigger project. Also, I use it to turn off my bedroom lights from the bed and have coupled it into turning off other things to be sure they're ready for the night as well.

I decided it was time to make some more of them, but the thought of hooking up thirty or so little fiddly wires on a protoboard kept me from actually doing it. What I needed was a custom PC board. I've designed a board before for a charger I came up with for the various lead acid batteries around the place <link>, but that project died when I found a really good battery maintainer to use commercially available. I still have one of the boards running, but it's only monitoring the battery voltage, not charging anymore. I may get back to that project at some point and come up with a simple battery monitor replacement, but right now I need an easier assembly technique and a custom board sounds like a great idea.

I dragged out Eagle <link> that had been hiding somewhere on my machine for months and updated it (of course) and started trying to use it again. Needless to say, I had to find a couple of tutorials to get me started again. I took the schematic for the sensor and came up with a board that looked like it would work, let it sit for a couple of days, revisited it and made a couple of changes then sent it off to OSH <link> which is SparkFun's old PC board service they farmed out.

I got the boards back a couple of days ago and assembled one of the three to see if it would work.

They're two inches square and purple. They're also thinner than I'm used to seeing, but that doesn't really seem to matter; they are strong enough to use.

When I got one of them loaded with components:

Yep, I'm still using the cheapest batteries I can find. I put the XBee and the Arduino side by side instead of vertically to meet a different form factor I couldn't try with the prototype. I'm still mounting all the active components in sockets so I can trade them out if necessary. I was lucky, it worked first try.

Well, that's partly a lie. The circuitry was fine and everything connected up OK, but I put the wrong profile on the XBee and it took some head scratching to find out what happened. Note to self: pay attention to what you name the profiles.

I went and got one of my famous rubber bands and packaged it up:

There's some things I might do differently on my next order, and in general. For example: if I flip the ftdi connector over to the other side of the Arduino it would make the height shorter and maybe easier to mount in a permanent enclosure. It might be good to actually include some holes for mounting the thing; I totally forgot that part. I did think of things like a place for a connector for the switch, but I put it too close to the switch to be easily connected. Lastly, more labels on the board. I had trouble telling which capacitor went where. Labels like C1, and C2 didn't tell me much and I had to keep looking at the schematic to assemble it. Of course, if you already have an example made, this problem doesn't exist, so maybe I'll just keep a good picture of it on my phone to refer to later.

The period from creating the artwork for the board and getting it back was long enough that I even forgot which way I pointed the Arduino and XBee. Sad I didn't put an arrow or something on the silk screen for the board. But, I guess we have to learn some things the hard way. At least I do. Nevertheless, IT WORKED !

I'm actually pretty happy with how it turned out. The idea of taking major components that I can buy for the most complex parts and just mounting them as modules on a board that interfaces them and has the interface components worked really well. I don't have to stock all the parts for a bare bones Arduino, I just use a cheap Arduino Pro Mini. I don't have to stock some radio parts or fiddle with RF alignment, I just use an XBee. The only parts are simple to install ones and not many of them.

Now, I have a bunch of work to do. I already had code on my Raspberry Pi to update the data base when a new temperature sensor appeared and that worked well, so I'm saving readings from two of them now (the prototype and the new one), but I'm not doing anything with it. The real objective for these is to put one in each strategic place around the house and use them to control the house temperature.

The plan is to measure the temperature and intelligently control the air handlers and compressors of my two heat pumps to adjust for warm spots in the summer and cold ones in the winter. I want to get out of the tub after a long soak in the winter and NOT freeze my butt off. I can use the air handlers to distribute warm air from the hot side of the house in the winter, and just reverse that in the summer.

I won't have thermostats at all, I'll network the entire thing and control it with an HTML interface. I may still leave a display up in the place of the thermostats since people expect to be able to look at one, but it won't have any buttons. OR, I may put a cheap tablet up on the wall with a browser running to control the entire house with.

This will mean a control board at each air handler so I can control various relays that work the fan, compressor and reversing switch that hooks into my XBee network as well. But hey, I talked a bit about that already <link> so I won't bore you until I actually start that part.

I'll need at least three more boards, and I may make the changes I talked about in the second order, but thinking about it, the changes are trivial and I can live without them. I also have other ideas about using something like this to monitor the moisture in the soil of my two new fruit trees, and as mentioned earlier, the state of the tractor batteries in the barn. See, I can put any sensor on the device and have it transmit whatever I want to my network. I may look at a motion sensor for the driveway to tell me when someone drives up. Doing that without wires would be really cool. That would mean some changes to the board for the different uses, but that also means that I GET TO MAKE CHANGES TO THE BOARD as well as try out some new sensor and code.

I'm definitely going to need some more batteries.

Tuesday, October 4, 2016

So, My Raspberry Pi Web Server Was Running Slow

I was sitting on a bar stool showing off my Pi web server that controls my house and had to wait 15-20 seconds for each screen change. Loading graphs was painfully slow and would pause in the middle with only half the graph showing. It was embarrassing. When I got home, I took a look and the load average was up in the double digits; something I had never seen before. Obviously, there was some process or other out of control that needed to be fixed. I was wrong.

Granted, it's my oldest Pi; a Pi 1 that I just keep because it's easier than bringing up my Pi3B to do the same job. I recently put a SSD on it, and it logs to a database server up in the attic, so it's been fast enough. Now, it was just crawling along.

When I went looking for what was causing it I found someone out there on the web was loading my data as fast as the process could be run. Don't misunderstand, there's nothing secret there and folk visit my site all the time to see what's different from the last time, and I've had something similar happen before; it was quite innocent. What most people don't realize is that a site that automatically updates by doing a periodic get, when put in background, will continue to update. So, you visit one of the news sites, hit the back button down on the bottom of the phone, the app disappears and you go do something else, and the app continues to run updating the screen you can't see. This can cause data overages and such, but the app is ready when you come back. This shows up in my logs as someone on the site for a very long time.

Almost all sites are polite about this auto-update and only update on a multi-minute schedule; I have my site update every 10 seconds because I want to double check and see that the garage door actually closed like it was supposed to. What was happening was someone had set up a loop that would grab the data again as soon as it was delivered. That caused a lot of database read activity and slowed the machine down a LOT. Of course, I didn't realize this at first and assumed I needed to check the efficiency of the data gathering steps.

I have a php script that gathers the data from my database and returns it to the web user called housedata.php. It's a rather simple implementation, so I took it and started timing the various operations by commenting out pieces and timing it using the 'time' command in bash. The stupid little process was taking 4.75 seconds on average to finish at first, but after some database query changes, it went way down; but all that did was allow the person out there to call my machine faster.

I looked at excluding the person by IP address using the features of the apache2 web server and succeeded in stopping the interaction quite nicely. That made me think about what else might be going on, so I took a closer look at the logs. There was the usual script kiddies trash looking for 10 year old vulnerabilities, search engines prowling around, and days worth of this person beating on my machine. I had fixed the problem, so I improved the speed of housedata.php a little more and called it done. The next morning, the person was right back in there with a slightly different IP address doing the same thing.

I added the new address to the web server exclusions and noticed that it was in a subnet of the internet provider that was being used. Ha! I excluded the entire subnet to stop the problem. The problem with excluding the IP addresses with the web server was that the web server starts a process for each hit. That takes time and machine resources, not a lot, but enough to notice over time. It looked like it was time to actually bring up a firewall to protect the little machine.

I already knew about 'iptables', but have you ever tried to use that thing? It's really hard to set up, and I could mess it up pretty badly leaving holes where there shouldn't be and locking myself out of my own machine. I shuddered at trying to get that working without a months worth of research, but then discovered 'ufw' a tool designed to help with that process. I did the dreaded apt-get update command and then an apt-get install ufw so I could try it out. Notice that I did NOT use apt-get upgrade! I'm getting really tired of having too much stuff on my machine replaced by well meaning folk out there. The last time I did that I wound up with a new slightly incompatible operating system (jessie).

Since I run headless (no keyboard or console), I was afraid of actually enabling the firewall since it would exclude port 22 and I wouldn't be able to get into the machine to do anything without dragging it to a TV set somewhere and poking around for hours sitting on the floor in front of it. Fortunately, the folk that put the package together left a note in one of the configuration files about this very thing and I did what they suggested. Gritting my teeth in expectation of failure, I started the process and it warned me that ssh sessions could be interrupted and asked for confirmation. I gritted a little harder and answered 'Y'.

It came up just fine and didn't affect the ssh session at all. I was on my way.

If you have to do this, one thing you'll find annoying is the huge amount of introductions, tutorials, promotions, and examples out there on the web that don't tell you what you want to know. Sure they tell you stuff that is valuable, but I didn't find a single one that covered what I needed to do; it was all trial and error. Painful trial and error. After about an hour I came up with an idea: look at the darn log file created by ufw to see what was going on. On the Pi, the log records are mixed in with other stuff in the file /var/log/messages. So, I set up a way to watch it and see what was happening:

tail -f /var/log/messages | grep UFW

After watching a while for the various things that were being dropped, changing the configuration, watching some more, I got it working perfectly for my purposes. I had a little annoyance with the order of the rules. See, when ufw (actually iptables, ufw is just an interface) sees a packet, it steps through its rules in order and stops when it satisfies the first one. So if you allow access to port 80 as the first line, you can't exclude a specific IP address later; it already let the packet through and stopped looking. So, put the stuff you want stopped first and then the stuff you want to allow later.

I allowed all the machines on my local network to get to the web server for various things, but only open port 80 outside the house. Here's the list I'm currently using:

pi@housemonitor:/var/log/apache2$ sudo ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN
[ 2] Anywhere                   DENY IN
[ 3] Anywhere                   DENY IN
[ 4] Anywhere                   DENY IN
[ 5] 80                         ALLOW IN    Anywhere
[ 6] 3551                       ALLOW IN
[ 7] Samba4                     ALLOW IN
[ 8]                ALLOW IN
[ 9]                  ALLOW IN
[10] 22                         ALLOW IN    Anywhere (v6)
[11] 80                         ALLOW IN    Anywhere (v6)
[12] 3551                       ALLOW IN    Anywhere (v6)

First, I allow port 22 from all internal addresses. Like I said, I worry about excluding my own access to the machine. Then a series of nets excluded because I saw them messing around. The address is where the annoying traffic was coming from, the two addresses that start off with 180 are for a Chinese web crawler for a search engine. It was hitting my machine every 30 minutes from two different addresses that changed within that range. I don't mind search engines, but every 30 minutes? The IP version 6 stuff is the default, I haven't gotten to it yet.

Port 3551 is for my APC UPS that I wrote about recently. That device is working really well and controls the shutdown of all my Pi's so I want the machines to be able to interact. Of course I use Samba to move files around, so there's an entry for that. The two 224 addresses are for ARP and such, I put the entries in just to keep them out of the log.

As soon as I did that, my load level dropped to fractional numbers; the machine finally had time to actually do things.

Also, since the person out there was getting time outs from not being able to get a response from my machine, its hits dropped to every 30 seconds or so. These hits were dropped at the protocol level, so they don't cause me any problems at all.

This rather busy screen shot shows the hits roughly every 30 seconds trying to load stuff, and each of them gets dropped with no response. The really annoying thing is that this person is STILL trying to get in. I've been working on this for a few days now and this robot doesn't have the smarts to try something else. I know it's a 'bot because it goes directly after the data server code without going through the web page. After I finished with the changes I let the machine run overnight and looked again, neither the web crawler or the annoying 'bot got in.

Success !

At least so far. Sure, I'll get annoying traffic again, but now I know how to stop it and have the means to do it relatively easily.

Don't misunderstand, I don't mind people looking at the site at all; I encourage folk to take a look. It's there not only so I can close my garage doors, but to serve as an example and source of ideas and suggestions. I just ask that you don't set up scripts to mess around with it for days at a time, and until now, everyone has been really nice about it. Some of my (ahem) ideas have come from people looking around and suggesting things. I've saved many a kid from a bad grade in a computer science class because they can steal code from me. And, there have been a couple of seriously interesting term papers written based on things they found here.

I'm actually contributing ... well sort of.

One last thing came out of this exercise. I had to put in a fake 'index.html' page because of the various 'bots that want to prowl around the site. What happens is the 'bot goes for the web site and then uses the URLs inside the index page to find other stuff on the site. Then it tries various 'exploits' to break in and do something bad on each of the pages. If there is no index page, it tries to get a directory listing and from there it starts messing around. If you put in a dead end index page, it can't get a directory listing and there are no URLs in the page to leverage from; the bot gives up and moves on. The script kiddies and the constant data loading came to the attention of the web monitoring tools at my ISP and they started expiring my IP lease a couple of times a day to break up the traffic. Each time they did that, I was off the network for a short time while the DNS servers were updated. I have code in place for this kind of thing, so I didn't have to do anything, but it got annoying. We'll see if my changes remove this problem.

All in all, this was both annoying and fun. I got to learn about new stuff, make changes that work really well to some of my code and have something new to brag about when I go to the bar.