My method for backing up a Raspberry Pi

Intro

I have a vast army of Raspberry Pis serving me (although recently I've been liking ESP32 for some of the simpler tasks I've used to use Pis for, and mini PCs for the more complex ones).  I just had my first SD card failure in one.  This was a bit more annoying than I predicted it would be, so I set out to come up with a good automated backup process for my Pis.  As with everything I do, there are plenty of good write ups about how to do this online, and you will undoubtedly find those more useful if you actually want to do this, but I will document what I did here for 1. hypothetical fellow weirdos, 2. myself from the future.

NFS Server

I have a home server, with all my bulk storage in it.  I primarily run Plex and Home Assistant on it, but I also host my music collection on it, which I share out to my desktop and other clients via NFS.  NFS is just the Linux version of network shared drives.  I won't go into details about how to set up NFS, but this is a good overview.

Backup Script

Once you have a NFS server set up, you can just mount a drive there on your Pi with write access.  I then use rsync to send directories to the network drive nightly.  Here's my script along with some notes.

I chose the directories with configuration and data that I cared about in them, although it should cover most uses.

Fixing Christmas lights with a BBQ lighter

I have an old Christmas tree with several independent prewired light segments on it.  About half of these segments no longer work.  I figured it was just a matter of finding the blown out bulbs and replacing them.  I also knew the sets always claimed that if "one blows out, the rest stay on", but in practice those claims seem to not pan out.

In researching how to find the dead bulbs I came across a product called the Light Keeper Pro.  I didn't really understand how this product worked, or even really what it was supposed to do, but it was only $20, and I was confident I could fix the lights with the right tools.

Quick detour here to say I love the company that makes this thing.  It came with three dense pages of instructions, and a full page letter from the CEO basically telling you that if you're willing to learn how this thing works you can fix your lights, and if not then it's your fault.  Here's a 40 minute video about how to use it, it's one of several of similar lengths they have online.  These people just really want us to all know how Christmas lights work.

 

The device has a lot of functions built in; it's really a Christmas light Swiss Army Knife.  The one I thought I'd be using is the bulb tester, where you just pull the bulb out and stick it in the top and it'll light up if it works.  There's a similar fuse tests, although the company reiterates several times that fuses are rarely the problem.  There is also a non-contact voltage detector, which I have several of already, but is nice to have on there.  It's only useful for faults where there is a break in the circuit, like a missing bulb, or a cut wire.  There's a bulb remover tool, which I haven't really been able to figure out, and haven't tried very hard because I don't have trouble just pulling the bulbs out.

The star of the show though, is the quick fix trigger.  The instructions explain you remove any bulb from a non-working section and insert the socket into the front of the device (essentially the device fits like a giant "bulb").  You then click the trigger several times, and the lights somehow come on.  You do all this while the lights are plugged into the wall.

I almost skipped even trying this because it seemed so absurd.  But once I figured out exactly what they wanted me to try, I did it, and it worked, over and over again.  There were probably 5 different sections on this tree that didn't work, and this thing fixed each one in 30 seconds.  Now, to be clear, it doesn't make blown out bulbs come back on, but it does make it so that the "one blows out, the rest stay on" function actually works.  After the section comes back on you have to replace the burned out bulbs with new ones.

It may not surprise you that this led to me learning a lot about Christmas lights.  Now you're going to learn a lot about Christmas lights too.

 

How do Christmas lights work?

They start out pretty simple.  50 bulbs, each with a resistance of about 2.5Ω are in series.  Their resistances add, and so overall the string has a resistance of about 125Ω.  You plug that into 120 VAC and you get about 1 amp flowing through them.  You can imagine that each bulb shares an equal portion of the voltage, so each bulb has 120 / 50 = 2.4 volts across it.  If you took a single bulb and put 2.4 volts across it, it'd light up the same as if it were in a set.  The filament is just a piece of wire, which is so thin that it heats up very hot when the amp is flowing through it, and it glows.  Eventually that filament wears out and literally burns out from the heat.  At that point, the filament is gone and there is a gap which the current can't flow over.  Since every bulb is in series, current can't flow at all, and the entire set goes out.

I took this picture from here and it shows the situation.  If your set has more than 50 bulbs then it probably has a multiple of 50 (100, 150, etc).  In that case it's just a few of these sets of 50 just all connected together at the plug, like the next picture shows.

How do "one blows out, the rest stay on" lights work?

The magic of these is entirely within the bulb.  The wiring is same as above, just bulbs connected in series, but the difference is a "shunt" in the base of each bulb.  The idea is that if filament burns out, then the current can instead travel over the shunt.  The shunt is much thicker, so it doesn't heat up and glow.

How do these shunts work?

This is the key to this entire post.  The shunts can't just be another piece of wire, because all the current would just travel over that instead of the filament.  They need to be "off" normally, and only get activated when the filament blows out.  The shunt is just a piece of oxidized aluminum wire.  The oxidation makes it high resistance, and when there is the normal 2.4 VAC across the bulb the shunt does not carry a current.  If a high voltage is applied to the shunt though, the current will flow through it and the oxidation layer will burn up and you'll be left with a low resistance wire.  This is called an antifuse.

How do we get a high voltage to the shunt when the filament burns out?

This just happens.  I said above each bulb is sharing the 120 VAC from the wall, equally.  However, if there is a gap in the circuit (like a burned out filament), then no current will flow, and the full voltage will build up at the gap.  It doesn't matter how much resistance is in the circuit, if it is open, and no current is flowing, then the full voltage will be present at that gap.  Therefore, when one of the filaments burns out, the shunt in that bulb gets 120 VAC across it, which is usually enough to burn up the oxide layer on it and turn it into a normal wire.  Sometimes the 120 VAC isn't enough though, and that's when the whole set fails despite the "one blows out, the rest stay on" shunts.

How do we fix them?

Now that we know all that, the solution is pretty easy.  Just apply a higher voltage.  You could do this with some sort of high power transformer (like a ballast from a florescent light), but you'd have to apply the voltage just long enough to trigger the stubborn shunt, and if you applied it too long all the lights would burn out.  You'd have milliseconds between when you fixed the shunt and you ruined the entire set.

Luckily there's a simple solution: piezoelectricity.  There are certain crystals that when you hit them they produce a high voltage burst, a static electric shock on demand.  Any time you press a button and there's a click and a spark that is piezoelectricity.  It's how BBQ lighters work, and it's how the Light Keeper Pro works.

All that the Light Keeper Pro is doing is creating a quick burst of high voltage and putting it on the circuit.  It's a weird combo of 120 VAC and few milliseconds of 15 kVDC.  The 15 kilovolts easily overwhelm the AC voltage, no matter where it is in its AC cycle.  The 15 kVDC would fry stuff throughout your house, except it's such a small amount of energy it is easily absorbed by the actual wires long before it can reach anything.  The only thing that burst has a chance of reaching, and effecting, is the very sensitive aluminum oxide coating which is preventing the shunt from carrying current.

And that's all there is to it.  You could do the exact same thing as the Light Keeper Pro with a BBQ lighter.  All it is is a convenient package and way to connect the bulb socket to the piezoelectric spark.

We Analyzed 425,909 Favicons

 https://iconmap.io/blog

Suspicious discontinuities

https://danluu.com/discontinuities/

This page is a wall of text and some charts, but it shows some really interesting patterns in a wide array of data sets.

How I DIY smart home sensors

Home Assistant

I've had a draft post about Home Assistant for years, which I haven't posted because I feel like my HA install is perpetually under construction.  If you haven't heard of Home Assistant, it's a LAN based, open source, smart home control center.  Typically installed on a Raspberry Pi, it has an absurd number of integrations with third parties.  While the UI of HA can be polished up to be pretty nice, its real value is in automatons that never require opening the UI.  This isn't a HA post so I'll stop talking about it, but I highly recommend playing around with it if you have any interest in smart home, and are willing to tinker a bit in exchange for not having to use cloud based systems.

Sensors

While I have a variety of sensors that serve particular purposes, I'm obsessed with collecting basic data for each area of my house.  Particularly, I like to measure the temperature, humidity, and light level on each level on my house (including attic and basement).  I do nothing with this information, but I look at the graphs literally every day, and they bring me great joy.  If you're confused right now, this is probably a good time for you to cut your loses and stop reading this post.  If you're excited for your own graphs, read on.

Data

While you can buy ready made sensors that measure these things, I've always built my own.  They are much cheaper, and you have way more flexibility if you decide you want to add something later.  Originally I started out with Raspberry Pis, and then Rasperrry Pi Zero Ws.  This works, but if you start wanting to do multiples of these, then the overheads of SD cards and high current power supplies start to add up.

I've always considered using an ESP32 (what an Arduino is based on) instead, but they are just more annoying to work with.  While a Raspberry Pi is a full computer, running Linux, an ESP32 is a microcontroller, which means you write a single program (typically in C), compile it and load it up, and when it powers up it runs that program, and does nothing else.

 

ESPHome

While the hassle of the ESP32 has never been worth the cost savings over the Raspberry Pi for me, this all changed when I discovered a project called ESPHome.  With ESPHome you connect some sensors to an ESP32, create a YAML file with the config, then upload the files to the ESP32, which will then begin sending the data to Home Assistant via an integration.  I couldn't believe how slick the setup was.  You can even update the config file and send the update to the ESP32 via WiFi without having to go to wherever you have it installed and hooking it up to a computer.  With ESPHome, setting up these sensors is easier with ESP32s than my custom Python scripts running on Raspberry Pis.

Hardware

These links are mostly dead, as these listing change often.  But, I'll provide them, and the price I paid, as a reference for you, visitor from the future.

ESP32 ($6.50 each) - There are a few versions of these out there, and I'm not an expert on the differences, but for our purposes I don't think they matter much.  Just note what pin layout you get, and make sure when you buy more they are the same layout.

BME280 ($24 / 3) - Temperature, humidity, and pressure sensors.  I used to use DHT22 sensors, but BME280s are: 1. more accurate, 2. use the I2C protocol, and 3. include pressure.  I can put two DHT22 sensors next to each other and while it's obvious the graphs follow each other, there is clear variation between them.  With two BME280s the graphs are spot on.  They are also much higher resolution, which makes the graph much smoother.  The I2C protocol allows you to share one pin across many sensors.  Each sensor gets an address and the host will cycle through them measuring each one.  This makes it quite easy to add another (I2C based) sensor later on.

BH1750 ($7 / 3) - Light sensor; also uses I2C.

USB Charger - I won't provide a link and cost for these.  The power requirements for ESP32s is much lower than a Raspberry Pi, under 500 mA vs at least 1000 mA to over 2000 mA for newer Raspberry Pis.  You should be able to use any random USB charger you have available.

Prototype Boards ($12 / 40) - Not required.  Used to hold multiple sensors together and wire everything up.

Headers ($14 / 120) - Used with the prototype board.

Jumper / Dupont wires ($7 / 120) - Used to connect sensors.  You can technically get by without these if you use the prototype boards, or you can use just these instead of the boards.

Build

Full disclosure: This isn't going to be the type of guide you can just follow along step by step and end up with something that works.  You'll have to understand what you're actually doing to get this to work.  This isn't intentional on my part, it's just the best I can do explaining this.  If you've soldered a bit before, and are familiar with wiring things up to Pis and Arduino you should be able to get it to work.

My goal is to build a "shield" from a prototype board, which will sit on top of the ESP32 and allow multiple I2C sensors to be plugged into it.  Since I2C generally use the same pin layout, the front of the board will have multiple header sockets aligned vertically, all connected to the same wires on the back of the board.  Those wires will go to 4 pins on the ESP32.  I use a few inches of solid core Ethernet cable to provide the wires.

This is the pinout of the style ESP32 I use.  There are a few common ones, and you have to find the one that matches yours.  The pins we care about are 3V3, GND, I2C SCL, and I2C SDA.  All the sensors I buy have pins in the order VCC, GND, SCL, and SDA, this is common, but something to check when searching.  It's not required to have the pins in this order, but if all your sensors have pins in the same order you can create a bus on the board where all the pins are wired in parallel to the 4 pins of the ESP32.

The way I wire the boards up is going to be hard to explain, but hopefully these pictures help.

Front of the prototype board

Back of the prototype board

Start on the front of the board with two 4 pin sockets, aligned vertically.  On the back of the board, wires are soldered up to the pins of those sockets, and run vertically down the board.  It's not clear in the picture, but there are exactly 8 solder points on the back of the board, for the two 4 pin sockets.  Each of the pins of the two sockets is directly connected to the same pin on the other socket.

At the bottom of the board, the wires run through the board, back to the front.  Looking at the front of the board again, the wires then run all over the board to where the pins are on the ESP32.  If you're using a different ESP32 pinout, the exact layout of the wires on the front will look different.  There are also 8 solder points on the front of the board.  Four of them are the electrical connections to the four pins of the ESP32. and the other four are just physical connections holding the top and bottom of each 20 pin header in place, those are technically optional.

Your ESP32 will then have two male headers soldered to it (possibly by you), which will then plug into the 20 pin female header on the prototype board.  Four pin male headers on the sensors can then be plugged directly into the four pin female headers on the board.  However, I have found using a short 4 wire jumper cable between the BME280 and boards will help keep the heat from the ESP32 from influencing the temperature reading of the BME280.  You could also just subtract an offset in software if you'd rather a neater look.  It's not pictured, but I use masking tape to cover all the exposed wires to prevent shorts and class it up a bit.

Software

The software step is way easier than the hardware.  First, follow the ESPHome getting started guide.  Then, when you have your YAML file, modify the following example to get it working with the BME280 and BH1750:

esphome:
  name: rec_room
  platform: ESP32
  board: esp32doit-devkit-v1

wifi:
  ssid: "MyWifiNetwork"
  password: "Password123"

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Rec Room Fallback Hotspot"
    password: "random_password_abc123"

captive_portal:

# Enable logging
logger:

# Enable Home Assistant API
api:

ota:


i2c:
  sda: 21
  scl: 22
  scan: True

sensor:
  - platform: bh1750
    name: "Rec Room Light"
    address: 0x23
    measurement_time: 254
    update_interval: 60s
    unit_of_measurement: lux

  - platform: bme280
    temperature:
      name: "Rec Room Temperature"
      oversampling: 16x
      filters:
      - lambda: return x * (9.0/5.0) + 32.0;
      unit_of_measurement: "°F"
    pressure:
      name: "Rec Room Pressure"
    humidity:
      name: "Rec Room Humidity"
    address: 0x76
    update_interval: 60s

 

Summary

I'll admit, that when I list this whole process out like this, it's a lot more work than I thought.  It's also not particularly cheap for each sensor package, at just under $20 each.  But it's hard to find sensors that plug in to the wall, instead of using batteries.  That could be a pro or a con to you, but I hate batteries.  These are also really rock solid reliability, and provide super clean data.  Plus, it's fun?

Feynman: FUN TO IMAGINE

This is an old video, but this is a new HD rip from the 16mm film.  I really recommend watching it if you haven't ever.

https://www.youtube.com/watch?v=nYg6jzotiAc

Radio Transmissions From Police Helicopter's Chase Of Bizarre Craft Over Tucson Add To Mystery

https://www.thedrive.com/the-war-zone/42021/radio-transmissions-from-police-helicopters-chase-of-bizarre-craft-over-tucson-add-to-mystery

On February 9, 2021, a U.S. Customs and Border Protection (CBP) helicopter encountered what was described as a “highly modified drone” hovering in controlled airspace above Tucson, Arizona. A Tucson Police Department (TPD) helicopter was called in to aid the CBP aircraft in its pursuit of the small aircraft, but the drone, or whatever it was, was able to outrun both of them as it flew through military airspace, deftly maneuvered around both helicopters with bizarre agility, and ultimately disappeared into cloud cover above the altitude the helicopters could safely fly. A police report previously obtained by The War Zone showed that the TPD crew described the drone as “very sophisticated / specialized” and “able to perform like no other UAS” they had previously encountered. Now we have the actual audio from the CBP helicopter’s interactions with air traffic controllers in Tucson during the incident, as well as audio from an after-action call between the TPD crew and the air traffic control tower.

How many Perseids will I see in 2021?

 https://blogs.nasa.gov/Watch_the_Skies/2021/08/09/how-many-perseids-will-i-see-in-2021/?linkId=127090324

 

Where Are The Robotic Bricklayers?

https://constructionphysics.substack.com/p/where-are-the-robotic-bricklayers

There seems to be a few factors at work. One is the fact that a brick or block isn’t simply set down on a solid surface, but is set on top of a thin layer of mortar, which is a mixture of water, sand, and cementitious material. Mortar has sort of complex physical properties - it’s a non-newtonian fluid, and it’s viscosity increases when it’s moved or shaken. This makes it difficult to apply in a purely mechanical, deterministic way (and also probably makes it difficult for masons to explain what they’re doing - watching them place it you can see lots of complex little motions, and the mortar behaving in sort of strange not-quite-liquid but not-quite-solid ways). And since mortar is a jobsite-mixed material, there will be variation in it’s properties from batch to batch.

Zip - How not to design a file format.

 https://news.ycombinator.com/item?id=27925393

> How do you read a zip file?

> This is undefined by the spec.

> There are 2 obvious ways.

> 1. Scan from the front, when you see an id for a record do the appropriate thing.

> 2. Scan from the back, find the end-of-central-directory-record and then use it to read through the central directory, only looking at things the central directory references.

I was recently bitten by this at work. I got a zip from someone and couldn't find inside the files that were supposed to be there. I asked a colleague, and they sent me a screenshot showing that the files were there, and that they didn't see the set of files that I saw. I listed the content of the zip using the "unzip -l" command. They used the engrampa GUI. At that point I looked at the hexdump of the file. What caught my eye was that I saw the zip magic number near the end of the zip, which was odd. The magic number was also present at the beginning of the file. At this point I suspected that someone used cat(1) to concatenate two zips together. I checked it with dd(1), extracting the sequence of bytes before the second occurrence of the zip magic number and the remainder into two separate files. And sure enough at that point both "unzip -l" and "engrampa" showed the same set of files, and both could show both zips correctly. Turns out engrampa was reading the file forwards, whereas unzip was reading the file backwards. 

‘Scared to Death’ by Arbitration: Companies Drowning in Their Own System

 https://www.nytimes.com/2020/04/06/business/arbitration-overload.html

The hair-dryer incident

 https://slatestarcodex.com/2014/11/21/the-categories-were-made-for-man-not-man-for-the-categories/

The Hair Dryer Incident was probably the biggest dispute I’ve seen in the mental hospital where I work. Most of the time all the psychiatrists get along and have pretty much the same opinion about important things, but people were at each other’s throats about the Hair Dryer Incident.

Basically, this one obsessive compulsive woman would drive to work every morning and worry she had left the hair dryer on and it was going to burn down her house. So she’d drive back home to check that the hair dryer was off, then drive back to work, then worry that maybe she hadn’t really checked well enough, then drive back, and so on ten or twenty times a day.

It’s a pretty typical case of obsessive-compulsive disorder, but it was really interfering with her life. She worked some high-powered job – I think a lawyer – and she was constantly late to everything because of this driving back and forth, to the point where her career was in a downspin and she thought she would have to quit and go on disability. She wasn’t able to go out with friends, she wasn’t even able to go to restaurants because she would keep fretting she left the hair dryer on at home and have to rush back. She’d seen countless psychiatrists, psychologists, and counselors, she’d done all sorts of therapy, she’d taken every medication in the book, and none of them had helped.

So she came to my hospital and was seen by a colleague of mine, who told her “Hey, have you thought about just bringing the hair dryer with you?”

And it worked.

She would be driving to work in the morning, and she’d start worrying she’d left the hair dryer on and it was going to burn down her house, and so she’d look at the seat next to her, and there would be the hair dryer, right there. And she only had the one hair dryer, which was now accounted for. So she would let out a sigh of relief and keep driving to work.

And approximately half the psychiatrists at my hospital thought this was absolutely scandalous, and This Is Not How One Treats Obsessive Compulsive Disorder, and what if it got out to the broader psychiatric community that instead of giving all of these high-tech medications and sophisticated therapies we were just telling people to put their hair dryers on the front seat of their car?

But I think the guy deserved a medal. Here’s someone who was totally untreatable by the normal methods, with a debilitating condition, and a drop-dead simple intervention that nobody else had thought of gave her her life back. If one day I open up my own psychiatric practice, I am half-seriously considering using a picture of a hair dryer as the logo, just to let everyone know where I stand on this issue.

River Runner: drop a raindrop anywhere in the USA, watch where it ends up

 https://river-runner.samlearner.com/

Teardown of a PC power supply

 https://www.righto.com/2021/05/teardown-of-pc-power-supply.html

You might wonder how the controller chip on the primary side receives feedback about the voltage levels on the secondary side, since there is no electrical connection between the two sides. (In the photo above, you can see the wide gap separating the two sides.) The trick is a clever chip called the opto-isolator. Internally, one side of the chip contains an infra-red LED. The other side of the chip contains a light-sensitive photo-transistor. The feedback signal on the secondary side is sent into the LED, and the signal is detected by the photo-transistor on the primary side. Thus, the opto-isolator provides a bridge between the secondary side and the primary side, communicating by light instead of electricity.

Try This One Weird Trick Russian Hackers Hate

 https://krebsonsecurity.com/2021/05/try-this-one-weird-trick-russian-hackers-hate/

DarkSide and other Russian-language affiliate moneymaking programs have long barred their criminal associates from installing malicious software on computers in a host of Eastern European countries, including Ukraine and Russia. This prohibition dates back to the earliest days of organized cybercrime, and it is intended to minimize scrutiny and interference from local authorities.

In Russia, for example, authorities there generally will not initiate a cybercrime investigation against one of their own unless a company or individual within the country’s borders files an official complaint as a victim. Ensuring that no affiliates can produce victims in their own countries is the easiest way for these criminals to stay off the radar of domestic law enforcement agencies.

 

DarkSide, like a great many other malware strains, has a hard-coded do-not-install list of countries which are the principal members of the Commonwealth of Independent States (CIS) — former Soviet satellites that all currently have favorable relations with the Kremlin, including Azerbaijan, Belarus, Georgia, Romania, Turkmenistan, Ukraine and Uzbekistan. The full exclusion list in DarkSide (published by Cybereason) is below:

Simply put, countless malware strains will check for the presence of one of these languages on the system, and if they’re detected the malware will exit and fail to install.

An A.I. Finally Won an Elite Crossword Tournament

 https://slate.com/technology/2021/04/american-crossword-puzzle-tournament-dr-fill-artificial-intelligence.html

Steam's login method is kinda interesting

 https://owlspace.xyz/cybersec/steam-login/

Draw an iceberg and see how it will float

 https://joshdata.me/iceberger.html

Predicting Hard Drive Failure with Machine Learning

 https://datto.engineering/post/predicting-hard-drive-failure-with-machine-learning

 

 

Simulating the PIN cracking scene in Terminator 2

 https://bert.org/2021/01/04/t2-pin-cracking/