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Spoofing EDID, fixing our Beamer

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As a hackerspace we regularly host user-groups and irregularly host talks and workshops and all of them need to use our beamer. Quite a downer then, that our beamer’s HDMI and DVI Input stopped working with newer laptop graphic cards. Especially since VGA started having it’s own issues: Dark slides transmitted over our long VGA cable cause the beamer to decide input has disappeared and switch the input off.

A look at the kernel messages with dmesg made the source of the problem immediately apparent. The CRC of the EDID the beamer sends over the HDMI/DVI cable is wrong. (Interestingly enough, the beamer EDID sent over VGA is fine). As a result, newer laptops decide that no HDMI/DVI cable has actually been attached. Nothing you can do. Certainly not with any user tools like xrandr or any Xorg driver or kernel module options. Believe us, we tried it all. (Even if a software solution would have been possible, it would certainly not have been convenient to hack each new speaker’s laptop and OS of choice on the spot.)

This needed fixing!

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WIFI+MQTT Smoke-Detector with 5yrs battery and ESP8266

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Read about Flocx’s current project, a battery-saving WIFI+MQTT-enabling cheap smoke-detector here: https://blog.flo.cx/2018/08/ikea-diy-smart-smoke-detector/

I wanted to do the same thing for my flat, but instead of using the IKEA one, I ordered two cheap 7€ SmartWares detectors from Amazon with 9V batteries that are advertised to give 5yrs battery life and otherwise identical hardware. Also instead of µPython I used Sming and C++. Just for the fun of it, I also added a voltage divider that measures the battery voltage at the time of alarm.

You can find my firmware on GitHub.

esp8266_smokedetector

Todo for the future: motivate someone to do this for realraum. ;->

Since all 9V smoke-detectors ICs basically use the same pinout with an I/O-function on pin 7 that pulls LOW when no smoke is detected and HIGH on alarm, they are all equally easy to mod. The SmartWares are smaller than the IKEA ones though, so I did not even attempt to fit everything inside the case. More accessibility traded for lower WAF :)

Note that there are 3V Lithium 10yrs battery life smoke detectors out there, which work a bit differently. For once, the ESP8266 does not run with 3.0V but needs true 3.3V, so at the very least you will need a cheap and tiny boost converter from AliExpress. Furthermore, they do not use a CS2105G0 based chip but a PIC which might not have an pin as CS2105G0-I/O-pin configured.

A word of warning: In order to conserve the battery, the circuit disconnects the whole GND when no smoke is detected. Thus GND and 3V3 of the ESP8266 may be short-circuited through the unpowered buck-converter, depending on your component. So just to be safe, remove the Wemos from the circuit before connecting it via USB.

containers, e.g. with systemd

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The more complex a program or application, the more likely it contains exploitable or otherwise dangerous faults. Containers are a way of limiting the damage by limiting an application access to the bare minimum. Ideally we would have a separate and instantly replaceable computer for every little daemon and service we run. Sadly, even with virtual machines, this would hardly be an efficient use of resources, so containers try to find a middle ground by allowing us to separate applications almost as if they were running on different machines, while actually sharing the same hardware and operating system kernel.

Several features come together to make this possible:
  • chroot
  • namespaces
  • cgroups

And it is a good idea to augment them with others:

  • seccomp-bpf syscall filter
  • packet filtering (ebtables)
  • virtual network devices
  • apparmor

Armed with these keywords, your week should now be filled with interesting and productive reading. :-)

If all you want are some opinionated basics however, read on:

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