I haven't thoroughly reviewed his web site, but I did take a quick look at his basic circuit for 8051 page, and in the brief period I was there, I noticed a few things that were a bit odd/inadequate:

• He states "P0 and P2 are multiplexed with Address and Data bus", yet the circuit he illustrates has neither external data/program memory, thus leaving P0/P2 available for GPIO.
• the use of an RC reset circuit. As we so often discuss here, proper reset generator circuits are so cheap these days there is seldom reason not to use them.
• Nonconventional configuration of external osciallator. Both the Intel and Philips manuals agree that when using an external oscillator with a CMOS/CHMOS device, the external oscialltor should be connected to XTAL1 and XTAL2 should be left as a no connect.
• Poor power supply design. There is no fuse or other form of overcurrent protection. Additionally there is no specification on the turns ratio of the transformer; selection of an inappropriate device could leave the input of the voltage on the 7805 regulator very high and result in overheating.

--Sasha Jevtic