Build a double sided UV LED exposure box for making PCB

I found a broken Samsung MM-N6 audio system and so I've decided to build myself a double sided UV exposure box using it's front panel since it already had an LCD display and buttons and the sliding motorized panel looked cool.

Before I get into more details about how it was build, take a look at this overview video.

Setting preferred units in Eagle CAD to metric or imperial

If you want to set Eagle CAD to display units in either metric or imperial, there is a simple command to do this.

SET Interface.PreferredUnit n

where n can be:
0 - the default value. Eagle decides if will display metric or imperial
1 - imperial
2 - metric

To change current units in Eagle CAD, simply paste the command in the command line, replace the n with your preferred value and press enter. To confirm that it worked, open the DRC window.

Imperial units in Eagle CAD DRC window

Metric units in Eagle CAD DRC window

How to build a zener and LED diode tester using a 555 timer DIY

If you have a bunch of salvaged zener diodes you need a quick way to sort them. In this article I describe how to build a simple test equipment that can be used to measure the breakdown voltage of a Zener diode. It can also be used to test LEDs and their color, since sometime a color LED can look white when not lit. This Zener tester is powered from a 9V battery so it doesn't involve dangerous mains voltage and can measure diodes up to 90V with the help of a 555 timer boost converter.

How water flows inside a washing machine

I had a broken Indesit WIE 107 washing machine and I was curious to know how water is distributed to 3 containers with only 2 solenoid valves and so I took it apart.

Washing machine water inlet distribution box teardown

Top side (original)

Top side (with markers)

ESP8266 library for EFM8 microcontrollers - Server mode

In previous article ESP8266 library for EFM8 microcontrollers was presented the ESP8266 module and how can be interfaced with a microcontroller in client mode. This article covers ESP8266 in server mode and how to send commands to ESP8266 over the internet.

Of course this is not a real web server although with an SD card whole HTML pages could be served. The purpose of this library is to extract queries from a URL requested by a client. This way for example you could change color and brightness of an RGB led using a color wheel in a phone app or control home appliances from anywhere in the world.