A Single Light to Monitor Them All in Real Time

The context

This week-end’s project was focused around building a simple indicator on my desk that alerts me of any problem at home in real time. That way, I don’t need to regularly check things around. Well, this may sound overkill for many people. But over the years, I’ve written a program to monitor many things around me without the need to perform a regular check myself. The only thing I was missing was some real-time monitor that would alert me whenever something urgently needed my attention.

Computers. I am a computer engineer, and as such I do have a few electronic equipment around. I also monitor the temperature, humidity in an out of the apartment and also water leaks with sensors, as I have some sensitive musical instruments in my home. In the past 2 months, the temperatures here have gone up to 37 degrees Celsius several times. These measurements have helped us, without air conditioning (which makes things worse on the long term), mitigate the heat. We could close everything when outside was hotter than inside, and open in the evening when the temperatures outside were coming close to the temperature inside.

Here are the temperatures my system measured for the last 5 days:

Where I came from

I already had a raspberry pi set up with a tiny monitor showing all the indicators and a big green light (or orange or red) showing the overall status. Something like this:

But this screen consumes 2.5 Watt when it is on, and only 0.15 Watt when it is off. This is a substantial difference, not even mentioning how much wear it causes the screen to be constantly on, just to show a green light!

The solution

A simple solution: use simple LEDs (which consume virtually nothing) controlled by the raspberry. So I built a first circuit to test the whole thing out:

Of course, that also works with the screen off, that’s the goal after all!

A printed circuit

I had to arrange things together on a smaller plate:

… and solder the whole thing together (yes I butchered the soldering, sorry):

That was a mess…

Buddha (you can see his legs on top of the picture) had a hard time coping with the mess, but he played his role perfectly and went into a deep meditation:

And of course I then had to use this very useful piece of equipment for the cables:

Trying it out

The first testing worked out as expected.

I just needed to print a little box for it with the 3D printer:

Final words…

Using a single green LED was not an option. If it was constantly on and green, it could simply mean that the program crashed… which is not good. I could make the LED blink… but any blinking inevitable catches the eye and is bothering. But two green lights alternating doesn’t catch the eye, and ensures that the program is alive.

On the other hand, the error state and the warning state with an orange light are blinking to make sure that my eye will see it:

And now I have an indicator on my desk telling me at all times that everything is ok. Or not.

The managing software is now on my gitlab: https://gitlab.com/jytou/monitoring-and-sensors/