Ben Eater : Clock

 Ben Eater is a wonderful teacher of digital electronics.  As I watch his youtube videos I am always amazed at how clearly and concisely he can explain and demonstrate circuits.  His big project was a set of videos explaining how to build an 8 bit microprocessor up from TTL components which I greatly enjoyed.  More recently he has shown how to make up a system based on the 6502 microprocessor.  Both sets of videos make me itch to follow his instructions to make my own system.  He has been kind enough to make available kits of parts containing everything needed to build his projects so I will do just that.  

Complete 8-bit CPU

It would be amazing to construct the 8-bit uproc but I don't know that I would have many uses for it once finished.  I have very fond memories of the 6502 from my youth, I used it at work around 1980 at British Aerospace and found its assembler language sensible and simple compared to other hardware languages I had to use at the time.  The 6502 was hugely successful and formed the basis of the Apple IIe, the BBC micro, Ataris and many others so I am looking forward to being reacquainted.  One of the many blessings of a daugher-in-law from California is that it makes it easier to purchase Ben Eater kits and get them back to England so I am now the proud possessor of 6502 kit and clock module.

The clock module is the first step of the 8-bit uproc project but is also useful for 6502 testing.  For a processor the actual clock speed will be 1MHz or greater, but when testing the system it is useful to be able to run the clock very slowly (c1Hz) or even single step it.  The 555 timer provides many different functions, it has been sold since 1972 in huge quantities. The Ben Eater clock circuit utilises three 555 chips to build our testing clock and demonstrate how it is configured.

There is a set of 4 videos, the first three going through configuring 555 as an astable, monostable and bistable device and the fourth one adds some simple logic gates so that we can produce a single tick or a regular tick-tock.  Ben describes how to choose ancillary resisters and capacitors to achieve the desired effect, how to connect the circuits and some additions to make the circuit more reliable by "debouncing".