Unfortunately Elektor published an old version of the statediagramm in the article. So I upload the actually version here.

Die Relais-Kontakte von RE1 und RE3 sind im Schaltplan falsch gezeichnet. Die Kontakte müssen als Öffner (normally open) gezeichnet werden. Im Layout ist die Kontaktbelegung korrekt. Die Klemme K11_1 sollte von L* in N* umbenannt werden. Die Klemme K11 ist der Schaltkontakt für das SMPS bzw. den Trafo.

In the year 2002 February I was doing similar project. I have tried both synchronous demodulation(Similar to this project) using Hex Inverter(CD40106) and PLL based design. I found PLL based design is very simple with few components and more flexible and we can adopt to many applications with small form factor. The PLL IC can sink 100mA which is useful for driving small DIP Relay. It worked well as diffuse scan sensor, retro reflective sensor and infrared beam interruption detector with ON/OFF delay Transmitter power, operating frequency and loop filter can be easily designed with one or two component value change. For additional improved performance we can use photo diode with inbuilt daylight cut-off filter or external filter sheet. I have used this sensor as a non-contact tacho meter and tested upto 6000 RPM(Equvalent to 100Hz) without any issue. For faster response we need to reduce the loop filter component values. For medium sensing range we can use photo transistor instead of photo diode for higher gain. Photo transistors are available with lens in TO18 package. I have used fresnel lens sheet along with transimpedance amplifier TDA2320(Now Obsolete) for range upto 50m using single IR Tx LED. Since same PLL VCO oscillator frequency is used for both Tx and Rx there is no frequency drift issues. Reference: LM567C datasheet TSL260 datasheet Figure 10. Proximity Detector Mondo-tronics Modulated Infrared Reflective Detector #3-337

It seems a few people have now built the project. Have you created an unusual implementation? Please post a picture of your setup! See the Version 1.2 Update pictures for inspiration....... Muiris.  

Version 1.4 * Sending of SMS via NEXMO service * Update SendMail.cpp to check for SMTP server availability * Add test buttons to send E-Mail or SMS on demand * Various small enhancements to the GUI * Move text strings in code to ROM to save RAM space using F() Since Vodaphone doesn't support the sending of SMS via E-Mail I decided to investigate a different alternative - Nexmo. This is a well supported internet based messaging system which shouldn't go away very soon. In my tests it has worked very well. Please clear the EEPROM beforehand (using the [Forget] button) if you build Version 1.4 on top of one of the previous releases. The EEPROM storage layout has changed. Otherwise strange settings can appear. Version 1.4.1 * Correct off-by-one error in SMS.ino substring selection - SMS sentCount remained at 0