I have that kit! It was great fun to build it, make some simple circuits, and trace the voltages through the "chip". The kit is really nice quality and thoughtfully designed.
This kit is actually from Evil Mad Scientist [1], the same people who make the EggBot and other nifty stuff. Their own site has a lot more information about it, and they sell it cheaper than Elektor. [2] They also have a similar μA741 op-amp kit. [3]
Back in the '70s I used to make blue boxes [4] with a bunch of 555s in them. This was probably not the best way to design a DTMF box - I remember I had a heck of a time keeping the frequencies stable. Woz's blue boxes probably worked a lot better!
The old elektor magazine was super good. Every issue had something on just about every level of competence in it. I learned so much from those. The most complex thing I built from them was the 2D graphics accelerator, hooked that up to the Beeb and wrote a fully functional vdu driver for it.
This kit is actually from Evil Mad Scientist [1], the same people who make the EggBot and other nifty stuff. Their own site has a lot more information about it, and they sell it cheaper than Elektor. [2] They also have a similar μA741 op-amp kit. [3]
Back in the '70s I used to make blue boxes [4] with a bunch of 555s in them. This was probably not the best way to design a DTMF box - I remember I had a heck of a time keeping the frequencies stable. Woz's blue boxes probably worked a lot better!
[1] http://shop.evilmadscientist.com/
[2] http://shop.evilmadscientist.com/tinykitlist/652
[3] http://shop.evilmadscientist.com/tinykitlist/762
[4] https://en.wikipedia.org/wiki/Blue_box