Switches to CPUs: Minutes counter
Вставка
- Опубліковано 8 вер 2024
- We make the minutes counter for the clock.
Part 1: Binary numbers - • Digital Logic Explained
Part 2: 2-input gates - • Switches to CPUs: 2 In...
Part 3: Relay based logic - • Switches to CPUs: Rela...
Part 4: Latches - • Switches to CPUs: Rela...
Part 5: SR Latch - • Switches to CPUs: Set ...
Part 6: Wired OR gates - • Switches to CPUs: Wire...
Part 7: Flip Flops - • Switches to CPUs: Flip...
Part 8: Ripple Counter - • Switches to CPUs: Ripp...
In the mid 1980's I was working for an electronics company in the test department with the ambition of moving into R&D. One day the manager of both test and production came to me and said that they had run out of 74C74's (Dual D type flip flop) and could 74HC74's be substituted. There was a mixture of 74C and 74HC devices all over the PCB which the substitution would be made, so I said OK. What I hadn't realised is that in this particular design both /Set and /Reset were sometimes brought low at the same time and that the truth tables for this condition were different. i.e. with both /S and /R low on the 74C74 both Q and /Q are Low and on the 74HC74 both Q and /Q are high. This is the only anomaly I've found but even now I still check the truth tables between 74 series families.
Yes, it may have something to with NAND vs NOR implementations of the latched. I personally prefer the term undefined, as it indicates use at your own risk. I believe the table I used was for a 74HC74, which is to tie it in later. Will divide the stream soon, one I’ll continue to use relays, the other I’ll move to 7400 series logic.
The use of BCD is a good idea. Much easier to read, and the logic to detect the overflow and reset to zero wasn't that complicated.
You tempted to make one?
@@DrMattRegan Yes, but maybe only part of one, as wiring relay D flip flops will get tiresome. I already have a relay ring oscillator, so a zero to fifty nine counter could be neat
@@mheermance 1-12 might also be useable as wall art!
I've just added like number 74. Nice.
Thanks. Enjoy!
Nice. Wonder how fast those little relays can switch? If it's less that 20ms you could half wave rectify the output of a small mains transformer and use that as a pretty stable timebase
Yeah, i'm still deciding what to do for timing. I'm tempted to use a pendulum. It's cheating a bit, because they are quartz crystal controlled. Interestingly i once saw the timing mechanism in Big Ben, a big pendulum. They used pennies on top to adjust the rate.
Neat
Thanks
Now do dekatrons.
Hmmm, i think i'll skip them. Was planning to go over Karnaugh maps and 7 segment displays. I'm trying to introduce the ideas as i need them to get to the finish. Any thoughts on this series?