My decade-old 4th generation iPod decided to blue screen on me, literally.
I love old stuff and I’m rather attached to this very first Apple product that I purchased 10 years ago. So I decided to turn to iFixit, the well-known DIY repair store for Apple products, for a replacement LCD screen.
I have always been an advocate on storage security (all types of security, actually). I like how iOS devices keep all files encrypted, even if you do not set a passcode on the device. They do this to facilitate quick erasure of files on the device — to erase all the data, they simply wipe the master key.
Erasing magnetic storage media isn’t difficult, but it is time-consuming. For solid state media such as SSDs and flash drives, the wear-leveling makes it difficult to ensure that all flash blocks have been securely overwritten. The answer to this is to encrypt everything.
Recently I have been busy building a Linux-based NAS and I decided to put this to practice.
What is EAP-SIM?
EAP-SIM is one of the authentication methods that can be used in an 802.1x or WPA Enterprise network. Specifically, it relies on the user’s SIM card to process a presented challenge. This has been used by some telcos to provide WiFi service without having to maintain a separate set of credentials. However, not all phones support EAP-SIM.
Since I’m already using a RADIUS setup at home, the use of EAP-SIM will eliminate the need to install my CA certs onto each device. But of course, there is still a fair bit of work to do…
Consumer Electronics Control (CEC) allows control of AV devices that are connected via HDMI. This is the feature of HDMI that enables your TV to automatically turn on and switch to the correct input when you switch on your set-top box, for example. It also allows you to control your set-top box using the TV remote (in some cases).
Electrically, the CEC bus is a single-wire bus that is shared between all HDMI devices, thus any CEC message can be received by all connected devices. Each device then claims one or more logical addresses on which it will receive direct CEC commands.
One interesting feature in the HDMI CEC specifications is Remote Control Pass Through, which allows button presses on the remote control to be passed through to HDMI-connected devices. I thought this feature could be used to unify the various remotes in my living room.
However, not all CEC devices are created equal. As usual, some manufacturers will deviate from the specifications, and/or introduce some quirks in their implementation (as you will see later). They also love to brand CEC with their own funky name, such as SimpLink or Anynet+.
Raspberry Pi as a CEC Bridge
As a quick and dirty way to check out the capabilities of my TV, I used a Raspberry Pi which has a HDMI connection that can be software-controlled. This also meant that I didn’t have to build my own CEC transceiver circuit.
Around this time last month, the haze (or what some people call smog) here set a record high level for the Pollutant Standards Index (PSI). This is what it looked like outside:
As our National Environment Agency only published 3 hour PSI averages, I thought it would be good if we could get our own measurements. The PSI used here is somewhat like the Air Quality Index (AQI) used in the US, and is made up of 5 components:
- PM10 particulate matter
- sulphur dioxide (SO2)
- carbon monoxide (CO)
- nitrogen dioxide (NO2)
Note that the AQI includes PM2.5 particulate matter whereas PSI does not. From what we can see, I would think that a major contributor to the PSI is particulate matter (PM).
I took a brief look at the projects such as the Air Quality Egg and PACMAN. They used either the Sharp GP2Y1010AU0F or the Shinyei PPD42NS. These sensors generally operate based on the light-scattering principle, by measuring the amount of light that is scattered by particles.
Chris Nafis has done a great job documenting the use of both the GP2Y1010AU0F and the PPD42NS, compared against a Dylos DC1100 air quality monitor. As the GP2Y1010AU0F requires a certain pulse waveform to be supplied to its LED pin, I would say that the PPD42NS is self-contained and thus much easier to hook up.
On the front, it has 2 pots labelled
VR3 that have been already factory-calibrated. The IR detector is covered under the metal can. Interestingly there’s a slot by the side labelled
SL2 which is unused. If you’d like to see what’s under the hood, Chris opened up the black casing and posted a photo here.
Looking at the date code grid on the PCB, the units look like they were manufactured in July 2012. The circuit consists largely of passives and an op-amp.
RH1 is the resistor heater which, in theory, could be removed to save power if there was some other method of air circulation.