IOT Projects

Battery Testing with Raspberry Pi

Recently I purchased a portable phone battery on clearance. I want to use it to modify my defunct Pokemon Go Gotcha band, which no longer holds a charge, to run off the battery pack. I realized that a battery pack could also be useful for powering other small electronics, such as the Raspberry Pi.

The problem is, I wanted to get an idea of how long the battery would last powering the Raspberry Pi. Figuring this out isn’t really all that hard. The tricky part is that I can’t stand over the Pi and watch it until it dies.

So instead I set up a simple cronjob task to do the job for me. I had a spare SD card, so I threw a basic fresh install of Raspbian on the card. I configured SSH and WiFi, then did a quick run of “crontab -e”, then droped the following at the end.

*/5 * * * * date >> /home/pi/date.txt

Simple.

Every 5 minutes, the Pi will now write the Date and Time to the file “date.txt”. It will do this until it can’t which would be after the battery dies, killing the Pi.

After charging the battery pack over night, I stuck the Pi on it and left it.

After checking back periodically, when I found the Pi was dead, I plugged it into a regular power source to retrieve the data. The result were both better than I had hoped, and not as great as I had hoped. The Pi started spitting out Time Stamps again after I plugged it back in, so I ended up having to skim through the file to find the time gap. I went ahead and truncated the data down to hour stamps until I came across the time jump from when the Pi had died and when I had plugged it back in.

So it turns out that the Battery pack will drive power for the Pi for around 12 hours. I also want to test this under a bit of a load and test how long it will power an Arduino writing to a remote database.

A Pile of Used Tech

I recently had an idea occur to me that I might be able to pick up used Raspberry Pis off of eBay more affordably than buying them new. I didn’t really find a ton of savings, but I did pick up an auction for a lot of various parts for fairly cheap.

I am not sure what I’m going to do with all of this, but it seemed like a deal for around $50. I was worried that it wouldn’t all be included, but it was. Not everything is what I had hoped though. Two of the three Raspberry Pi 2s seem to be dead. I’ve tried several trouble shooting methods so far. They turn on, but don’t seem to real SD cards at all.

The arduino is a genuine Arduino, which is nice, but its a fairly older model. Not a huge issue, but it is what it is. The screens were a nice bonus. I’ve been looking into getting a screen of some sort of my Pis, possibly for a RetroPi handheld build. I have not tested the larger screen yet, it seems to work off of a funky daisy chain of an extra board and some cables. I did get the smaller screen working… ish.

It’s a nice little touch screen that fits nicely on top of the Pi. I have not had a chance to properly troubleshoot it, but the touch works kind of funky on it. For one, it seems to function more like a track pad than a straight touch. Two, the mouse cursor only wants to move along a diagonal axis across the screen.

This all kind of feels like a configuration issue however, so there is some hope. Plus I am not sure I really need a touch interface for a RetroPi handheld build.

There’s some other fun stuff that I have not had a chance to mess with yet. There were a ton of ultra sonic sensors. I’m not sure what exactly these could be useful for, but I am wondering if they would be able to do 3D imaging of an object or a space.

There’s some funky board with a digital display on it that seems to be some sort of power board. I am not sure I’m going to have a use for this at all.

Lastly, there is a Raspberry Pi camera module. I have not had a chance to test it out yet, but like the screen, this was something I’ve been wanting to try out.

Saving a Slice of Raspberry Pi

Raspberry_Pi_LogoSo of all the things on the network, the DNS and DHCP server are pretty important.  Especially because my experience has been the router the ISP provided is kind of mediocre at doing the DHCP job.  So when the Raspberry Pi I’ve tasked with doing the work started flaking out I was a little worried.

After some investigation, it seems the SD card had lost a sector, or whatever the equivalent thing is to a sector on flash memory.  These things do have a bit of a limited life and this particular one was a small 4GB card that was a little older.  Four gigabytes isn’t even above the recommended size for the Pi, but I knew I wasn’t planning on putting a lot on it.  Problems arose when it started dying though.  There actually isn’t much using the PiHole, some of the things my wife does with coupons and such I suspect might get blocked and I don’t want the headache of dealing with trying to manually whitelist things and complaints that this and that isn’t working.  The DHCP is another issue.  When the DHCP server disappears, it seems anything using it simply can’t connect to the internet.  I have a lot of static assignments but there’s quite a few assigned by the server.

I may have to look into setting up a secondary backup server, maybe on one of the CHIPs even.

I started out simply re-imaged Raspbian onto a fresh card and setting things up again following the tutorial I had posted.  Everything went pretty smoothly except that I was now out my old config file and would have to go through the hassle of recreating all of the changes I’d made adding and removing devices.

So I went with a new strategy, why not just clone the old card to a new one.  Unfortunately, Win32 Disk Imager, the recommended tool for imaging these SD cards, couldn’t read the whole card, it got hung up and failed partway in.  So I turned to my laptop and Linux hoping for something more robust, which I found in ‘dd’.  It probably stands for “Disk Duplicator”, but don’t quote me on that.

I started running dd to make an image of the old card to put onto a new card, unfortunately, it also failed, like Win32DiskImager.

Back to Square One…

After some searching, I found this post suggesting something called ddrescue.  Most of it wasn’t anything I needed aside from the following.

sudo apt-get install gddrescue
sudo ddrescue -v /dev/sdb /dev/sdc

A few things of note.  My laptop, like many, has a build in SD slot, I added a second using my USB card reader.  I opened the disk manager to get the path to each card, /dev/sdb and/dev/sdc.

This command also hit an error at the same point as both Win32DiskImager and the “dd” command, but it pushed on through, recovering everything else.  At this point it’s a matter of hoping that one bad spot wasn’t int he middle of an important file.