I discovered fischertechnik many, many years ago, in 1970 when I was a teenager. The first box was a Basic Box 50 with gray blocks. 

I used to play with Lego and Meccano, but fischertechnik offered the perfect combination of both. Later on, I went into motors, statics, electro-mechanics (em1) and electronics (ec1), till mid-1980's. 

Many years after in 2000 at the Franz Carl Weber toy shop in Geneva, I discovered the new range with black blocks and the Intelligent Interface, actually a micro-controller. So I started again, playing with the pneumatic kit, which is really outstanding. Other kits came after.

In 2009, I went from 8 bits to 32 bits, changing my Intelligent Interface and Extension Module for two Robo TX controllers. I went on the discovery of the new development environment with the I²C bus as well as the niceties of the high speed controllers. In 2015 came the Robotics TXT with enhanced performance. In 2021 was launched the TXT 4.0 Controller, with further enhancements.

I'm mostly interested in industrial robots and mobile robots. I build my own advanced and smart sensors leveraging the support of the I²C protocol.

The basic element is a 15 x 15 x 30 mm block. 
It used to be light gray, it's now black. Both are fully compatible.