Self-made fischertechnik Robo Extension
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Self-made fischertechnik Robo Extension based on a ATmega328

Photo of ftroboext

I own a RoboInterface (yes, the old) from fischertechnik, but no Extension module for it. It's difficult to find some now, so I build my own. This repository contains the hardware as EAGLE files and the software as an Arduino sketch. The PCB is designed to fit nicely into a box (Art.Nr. 130961).

More information (in german) can be found on my blog.

I currently have two unpopulated PCBs here, contact me if you have interest in them.


The hardware is quite packed because it has to fit inside the box. This is also the reason why there are only four inputs (I1-I4). Everything is SMD for the same reason, but can be hand-soldered quite well, the biggest problem is the ATmega, but it is doable.

The hardware has a few bugs, see below. Some will be fixed in a new revision, some are impossible to fix. The biggest problem is, that the voltage on O2,O4,O6 and O8 can not be controlled, they are always the same as O1,O3,O5 and O7. This is because the driver has only one enable pin for both outputs, a fact I missed when selecting the chip.

Revision A

  • Footprint for C2 is wrong (too large)
  • Footprints for the connectors are a bit large
  • EXT header is mirrored/label is wrong
  • The /SS pin is not pulled low. To fix this, cut the ADDR1 pin from the header, solder it to GND (the pin next to it) and remove R14.


The protocol for the extension module was reversed-engineered by thkais and can be found on this website

The current software implements the basic functionality. Analog values are not implemented. Only a single extension, EXT1 is emulated and chaining is not supported.


This is project is not affiliated or endorsed by fischertechnik. It's just a project by a fan.