Some 13 years later, I’ve done a little revision to the Modutronic Messmaker circuit schematic. The Messmaker was intended to be a “beginner” build, and this new revision removes some complexity (and cost). The original version is also still available here and from a link on the page.
The original version includes a direct output from the 555, as well as inputs for the LM567 AM and the 555 CV in. My original thought was that these would be cool features for a beginner’s circuit, giving one easy access to some modular-style interconnectivity. However, all these years later, even I have rarely used these features. The quick & dirty nature of this circuit also means they don’t work the way one might expect with other modular stuff, which has become more common.