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Practical Electronics/Circuits to make
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
This part of Practical Electronics is a repository for circuits that have been made and tested, and can be made by you, using the diagrams presented here.
They range from simple plug-in modules for prototyping to more sophisticated modular counters and so on.
Plug-in Modules
Modular Multifunction Counter