The clock circuit (Basics)

Day 15

     Shipping notification has been sent on 10 of the relays I have on order hopefully I will have them in hand within a week and a half. Just in time for the next order to be placed, hopefully the other set arrives by then as well so I can make a full decision as to which supplier to use. 

     At the outset the clock looked to be 1 of the simplest sections of this build having now delved into many of the various pieces and seeing how the clock will need to behave I have the feeling this is a much bigger portion than first glance will tell.  The basics of the clock is a simple recursive chain of 4 relays with capacitors in between to add a slight delay and allow the clock to pulse fully at any given moment 2 of the relays are on and as such we can derive a square wave using a simple Boolean expression. The big trouble comes in when you understand that this clock needs to be started and stopped in such a way as to not give errant pulses and also needs to be able to be single stepped through it's various states this adds a level of complexity not initially seen.  I think this will be broken up into several days of chasing down answers.

     For today we will focus on the 4 main relays and their capacitors The 4 relays are labeled "A" "B" "C" and "D" each coil is attached to the capacitor and the normally open contact on 1 of the prior relay's switches A to D, B to A, C to B, and D to C the common contact of that switch is connected to the normally closed contact of a different switch on the prior relay, the common of which is connected to voltage. This means that once the circuit is set to running it will continue to run indefinitely without any assistance from us. However it also means we cannot control it without using some control circuitry. Which we will begin to breakdown in Saturdays post. 

     On the physical end this basic clock has only 8 schematic parts which are actually made up of 24 discreet parts the 500uF capacitors used are actually 5 100uF caps wired in parallel the part Harry uses is a non polarized style and is the exact piece I intend to use as well.  It is from www.allelectronics.com part number is NC-100.  I intend to list in a separate post in the future what and where I sourced all parts from so they can be easily found from a single page but I will also continue to discuss them in their related posts.