I have designed those circuits for my own hobby use and are presented here as is. I have tested the circuits presented in this page but there is no guarantee that the circuit descriptions and diagrams are entirely correct. I will try to correct all the error in the circuit diagrams when I or somebody else find those.  
* Audio circuits  
* Video circuits  
* Computer circuits  
* Data communication circuits  
* Light effects and controllers  
* Measuring equipments  
* Power supplies  
* Telephone circuits  
* Other circuits  
And more!
bignassty: Nice, I'm going to have to bookmark this.