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Sunday, November 14th, 2021

New Leffakone Infrared Receiver

Categories: [ DIY/Arduino | TV/Leffakone ]

Several months ago, the leffakone infrared receiver started to misbehave. There were a lot of errors in syslog about spikes in the signal, and the problem seemed to come from the serial port on the motherboard rather than from the homebrew IR receiver, connected to the serial port, that I had built in 2002 or 2003 and that I had been using with lirc ever since. One of the symptoms was that unloading the lirc-serial kernel module caused the computer to freeze, while testing the receiver with an oscilloscope seemed to show that it was working correctly. For many months, I was too lazy to do something about it, as using a keyboard with a long enough cord was enough to control leffakone. During the last autumn vacation, I tried to test the receiver with the serial port on minikone, but the latter seems to deliver only 1.2V signals, when the receiver expects at least 7V to power its onboard voltage regulator. So that was not very conclusive.


At the same time, I had the idea of building a CO2 monitor using a Jeenode I had lying around, and somehow I wondered if the IR receiver module would not just fit into one of the Jeenode's ports. Guess what? It fits perfectly, allowing to use the IRQ pin as the input, which is exactly what the Arduino-IRremote library suggests to use. Writing the software was a bit of a headache, because the library assumes that the compiler would run with the -flto option (and the compilation ends with an error if it is not set), but my custom Makefile somehow fails to compile the code correctly if I enable that option. Thankfully, you can get around the problem with #define SUPPRESS_ERROR_MESSAGE_FOR_BEGIN. After that, the program is quite straightforward: configure it for the RC5 protocol (as this is what my remote control produces), read a code and write it to the serial port if it matches the RC5 address. I also added a new feature: if the code is the power on button, it would set a pin to HIGH for a short while, allowing to switch the computer on. I used the Jeenode USB as it has an on-board USB-to-serial adatpter, which makes it perfect to connect to a modern computer. I had one reed relay left from the timer and despite being rated for a 5V control voltage, it works with the Jeenode's 3.3V signal. The Jeenode is connected to the computer with a USB cable where I have replaced the USB Type A connector with a Molex connector so that I can use one of USB headers on the motherboard. Crimping the very small contacts was difficult as I don't have a crimping tool, but the connections seem to be working despite having done quite a poor job of it.

Yesterday, I installed the extra reed relay and the Jeenode onto the PCB that holds the relays of the timer, and now it's inside leffakone and working well. And since I forgot to take a picture, there is no image of what it looks like. In addition, I'm quite happy I have been able to do this project by using only bits and pieces I already had (the Jeenode, the headers, the reed relay, the IR receiver module, the USB cable, the Molex contacts and housing).

[ Posted on November 14th, 2021 at 11:56 | no comment | ]

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Tuesday, November 2nd, 2021

CO2 Meter

Categories: [ DIY/Arduino ]


The last issue of Make: magazine had an article about building a CO2 monitor. The concentration of CO2 is apparently a good estimator for the concentration of SARS-CoV-2 in the air, which is correlated to the risk of transmission. The article suggests keeping the concentration of CO2 under 800 ppm when people are wearing masks.

The Make: article proposes a green-yellow-red light indicator, where the light is green when the concentration is below 1000 ppm, yellow above that level and red when it goes above 2000 ppm. These values are rather about indoors air quality and not directly related to limiting the transmission of SARS-CoV-2.

An article from NIST however indicates that the 1000 ppm limit has no basis whatsoever so I decided to use the 800 ppm limit instead and a rather arbitrary limit of 1300 ppm based on looking at Figure 2 in this article which seems to indicate that some cognitive abilities drop around that concentration.



The device itself is quite simple: it has an on/off switch and a single two-color LED indicator, red and green. The yellow color is obtained by turning on both green and red colors at the same time. It also has a small hole where a paperclip can be inserted for triggering the calibration procedure. The holes next to the power switch expose the CO2 sensor and its temperature/humidity sensor.

Inside the box there is an Arduino-like Jeenode I had lying around with an AA Power board (I have no idea if these are still sold, I've had them around for over ten years). The AA Power board is meant for a single AA battery, but it cannot provide enough current, so I removed the battery clips and connected it to a 2-AA battery holder, via the switch. It seems to be working well with two NiMH rechargeable batteries.

The CO2 sensor is a Sensirion SCD30. It is quite expensive (about 50 EUR), but has an easy to use I2C interface and is the most accurate of the sensors presented in the Make: article. The software is quite trivial (if you except the calibration procedure, see below), and available here. The device automatically makes a measurement ever two seconds, the program reads it and updates the LED accordingly. That's it.


There is an automatic calibration procedure that requires to keep the sensor powered for at least 7 days and put it in fresh (outdoors) air at least an hour per day. This is not very practical given that I've estimated that the batteries would last about 25 hours (20 mA for the ATmega, 17 mA for the SCD30, 10 mA for the LED at 3.3 V, with maybe a 80% efficiency for the power board with two 1900 mAh batteries at 2.4 V). There is however also the possibility to expose the sensor to air with a known CO2 concentration and tell it the actual value it is measuring. It then uses this value as a reference point for subsequent measurements. The device is apparently sensitive to changes in shape (e.g. when subjected to mechanical stress during transport) so as a portable device it probably needs to be regularly re-calibrated.

The calibration procedure is simple: place the device outdoors, wait about 2 minutes for it to settle, then introduce a paperclip into the hole and press the button underneath it; the LED will be flashing red. The device will take repeated measurements every 2 seconds, and when a succession of 10 measurements is considered stable enough (i.e. the absolute value of the difference between the first and last of those is at most 1, and the sum of the absolute values of each measurement with its previous one is at most 10), it sets the calibration value to 416 ppm (which seems to be about the average value in 2021). As the device is accurate to +/- 30 ppm, the exact value does not matter so much. The device then returns to its normal operation mode, showing a green, yellow or red light.

What next?

Put a sticker on it with some indications about the LED colors and the reset button hole.

[ Posted on November 2nd, 2021 at 23:22 | 2 comments | ]

Thursday, September 30th, 2021

Hot Sauce

Categories: [ Cooking ]

As I cannot find any Blair's Original Death Sauce in shops, I decided to reverse-engineer it, from memory. This is the result.


  • 25 g carrot
  • 11 g freshly grated garlic
  • 3.5 g fresh coriander leaves
  • 5 g mineral salt (Seltin)
  • 1.5 g powdered paprika
  • 0.2 g smoked paprika
  • 4 g sugar
  • 1.5 g powdered onion
  • 0.5 g dried parsley
  • 10 g tomato concentrate
  • 15 mL lemon juice
  • 150 mL Poppamies Habanero sauce (1 bottle)
  • water


  • 1 very small saucepan and matching kitchen stove
  • 1 0.1 g-precision scale
  • assorted measuring spoons (15 mL , 50 mL)
  • 1 clean and empty habanero sauce bottle (or another container for the leftover sauce).
  • 1 clean small funnel that fits into the bottle
  • 1 electric kettle


Chop the carrot finely, rinse and chop the coriander leaves.

In a very small saucepan, boil 1/2 dL water and add the carrots. Let it boil, then add the garlic, coriander, salt, paprika, smoked paprika, sugar, powdered onion and dried parsley. Let boil until the carrots are soft, stirring from time to time (keep an eye on it, it takes only a few minutes). If the water evaporates too quickly, just add more water and let it boil again. Then add the tomato concentrate, lemon juice and habanero sauce and boil once more.

Blend the preparation with an immersion blender until smooth and set aside.

Rinse the empty habanero sauce bottle, and preferably get a second bottle, as there will be more than 150 mL sauce.

Boil water in a kettle and use it immediately to fill the bottles and the screw caps to sterilize them. Also pour some of that water in and outside of a small funnel. Estimate the thickness of the sauce, add boiled water and stir to make it thinner. I added 30 mL water, maybe 20 mL would have been enough? Then empty the bottles (careful, they are hot) and pour the sauce into them with the funnel. Put the screw caps and store in the refrigerator. I use on such batch over several months, it seems to be keeping well.

[ Posted on September 30th, 2021 at 22:47 | no comment | ]

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Sunday, April 11th, 2021

OpenARC with Postfix on Debian 10 (buster)

Categories: [ IT ]

Gmail started to complain recently that the messages forwarded by the trivial mailing-list hosted on my server did not pass the ARC validation. As Google already considers e-mail coming from my domain as spam (but strangely, not the emails forwarded by the mailing list on the same domain), I did not want to risk to see my e-mail treated as even less worthy to be delivered to the Valued Customers of Gmail (i.e., probably half the world) than it is now. And I wanted to look into ARC anyway. But the installation is not trivial, there are no official Debian packages, and no clear tutorial on the Web, so here's what I did. It may work for you or not.

This tutorial assumes you already have configured postfix with opendkim, and they are running on a single computer on a Debian 10. The configuration example expects postfix to run as chroot and uses the private key configured for opendkim.

All the following commands need to be run as root or through sudo.

Install the package

Add an apt source by creating the file /etc/apt/sources.list.d/openarc.list and write:
deb https://download.opensuse.org/repositories/home%3A/andreasschulze/Debian_10 /
Then run:
curl https://download.opensuse.org/repositories/home:/andreasschulze/Debian_10/Release.key | apt-key add -
apt update
apt install openarc
If you don't want to run curl as root, you can run that command instead:
curl https://download.opensuse.org/repositories/home:/andreasschulze/Debian_10/Release.key | sudo apt-key add -
This will install openarc 1.0.0 beta3-3, but the package's post-installation script has a bug, so the installation fails. To fix it, edit /var/lib/dpkg/info/openarc.postinst and comment-out line 62 which contains
  ln -s ../../var/lib/supervise/openarc-milter /etc/service/

Then run as root apt install openarc again.

Configure OpenArc

Create /etc/openarc/keys and copy the key from opendkim (e.g., /etc/opendkim/keys/example.private) into /etc/openarc/keys/. Then copy /etc/opendkim/TrustedHosts into /etc/openarc/.

Create /etc/openarc.conf (or create one such file based on /usr/share/doc/openarc/openarc.conf.sample.gz) and modify the following directives (without the quotes around the values, of course):

  • AuthservID: the name of the server (e.g., “server.example.com”)
  • Canonicalization: the value “relaxed/simple”
  • Domain: the domain namd (e.g., “weber.fi.eu.org”)
  • FinalReceiver: the value “no”
  • InternalHosts: the value “/etc/openarc/TrustedHosts” (if there is a such a file)
  • KeyFile: the path to the private key (e.g., “/etc/openarc/keys/example.private”)
  • OversignHeaders: the value “From”
  • PidFile: the value “/var/run/openarc/openarc.pid”
  • Selector: the value of the opendkim selector (see Selector in opendkim.conf)
  • Socket: the value “local:/var/spool/postfix/var/run/openarc/openarc.sock”
  • Syslog: the value “Yes”
Create /var/spool/postfix/var/run/openarc that will contain the socket:
mkdir /var/spool/postfix/var/run/openarc
chown openarc:openarc /var/spool/postfix/var/run/openarc
chmod 750 /var/spool/postfix/var/run/openarc
Add the postfix user to the openarc group so that postfix can access the socket (run as root):
usermod -a -G openarc postfix
Create a systemd service file /etc/systemd/system/openarc.service with the following content:
Description=OpenARC Authenticated Received Chain (ARC) Milter
Documentation=man:openarc(8) man:openarc.conf(5) https://openarc.org/
After=network.target nss-lookup.target·
ExecStart=/usr/sbin/openarc -c /etc/openarc.conf

The UMask directive is especially important, so that /var/spool/postfix/var/run/openarc/openarc.sock is readable and writable by the members of the openarc group (i.e., postfix). OpenDKIM has a UMask directive, but OpenARC does not.

You can now start the service with
systemctl start openarc

Configure postfix

Edit /etc/postfix/main.cf and add the socket to the smtpd_milters and non_smtpd_milters lists (you may already have other milters configured, such as OpenDKIM):
smtpd_milters = unix:/var/run/opendkim/opendkim.sock,
non_smtpd_milters = unix:/var/run/opendkim/opendkim.sock,
Finally, restart postfix:
systemctl restart postfix

You can now test your OpenARC setup with the tools provided by openarc.org.

[ Posted on April 11th, 2021 at 20:23 | 1 comment | ]