EEVblog #801 - How To Design A Digital Clock

[EEVblog]

The next step for Ahmed Mohamed
How to design your own digital clock from 4000 series CMOS chips.
Dave reverse engineers a DIY clock he built back in the 1980's as a teenager (he lost the schematics, twice!)
Before the days of microcontrollers, cheap PCB's, and internet mail order parts, you built stuff on veroboard using discrete parts from your junk bin salvaged from old teardowns.
Does it use Texas Instruments chips from Radio Shack? :-D

Schematic: http://www.eevblog.com/files/DigitalClockSchematic.pdf

Datasheets of all your favourites:
https://www.fairchildsemi.com/datasheets/CD/CD4013BC.pdf
http://www.nxp.com/documents/data_sheet/HEF4040B.pdf
http://www.ti.com/lit/ds/symlink/cd4518b-mil.pdf
http://www.ti.com/lit/ds/symlink/cd4026b.pdf
http://www.ti.com/lit/ds/symlink/cd4511b.pdf

[Cliff Matthews]

Why was, or better put, who marked this as private?

[Delta]

Please sign in to see this video???

[AF6LJ]

I built one in the 70's using TTL it was a fun project.
This is a good beginner's project for someone learning digital logic, you really don't need a schematic, it is dead simple.

[zapta]

Why was, or better put, who marked this as private?

The clock had a Y2K bug. Dave is fixing it right now.

[WN1X]

Why was, or better put, who marked this as private?

I guess Dave doesn't want us to know what time it is 

[Cliff Matthews]

Please sign in to see this video???

I am signed-in and looking at my "EEVblog just uploaded a video" email. I'd guess there's so much activity, they've put restrictions on anything with this young lads name in it...
Update: After being posted 35 minutes ago, I can now watch it (screen grab from just 10 minutes ago..) - Draw your own conclusions...

[Barny]

One post on Twitter bevore he wrote that he shows his clock with many wires, he asked a company which uses explosives if he is allowed to visit them.

I think he have now some unwantet visitores which have many questions. 

[SeanB]

Works for me, don't know about the rest of you.........

CMOS, because you could drive LED displays directly from them at 5V without much risk of blowing up displays.

[Barny]

Strange.

Now, its working for me too.

[han]

Next step??


I found the frist step in youtube:
https://youtu.be/kHk_6Vh4Qeo

[EEVblog]

Why was, or better put, who marked this as private?

No one has access to my account but me.
I set it private because people were going to bitch about the 360p only. Turns out more people bitched about it being private 

[tggzzz]

Dave reverse engineers a DIY clock he built back in the 1980's as a teenager (he lost the schematics, twice!)
Before the days of microcontrollers, cheap PCB's, and internet mail order parts, you built stuff on veroboard using discrete parts from your junk bin salvaged from old teardowns.

Here's my variant, from around 1973: https://entertaininghacks.wordpress.com/2015/02/21/a-40-year-old-hack-disinterred/ and construction techniques: https://entertaininghacks.wordpress.com/2015/02/21/vintage-hacking-or-the-past-is-a-foreign-country-they-do-things-differently-there/

A few years earlier I built a 8 bit counter from discrete resistors capacitors and transistors, all salvaged from other equipment since I didn't have enough money to do otherwise. I used it to turn my radio off after a preset time.

[EEVblog]

I am signed-in and looking at my "EEVblog just uploaded a video" email. I'd guess there's so much activity, they've put restrictions on anything with this young lads name in it...
Update: After being posted 35 minutes ago, I can now watch it (screen grab from just 10 minutes ago..) - Draw your own conclusions...

There is no mystery, there is no restrictions being put on things. I made it private because it hadn't finished processing yet.

[EEVblog]

Here's my variant, from around 1973: https://entertaininghacks.wordpress.com/2015/02/21/a-40-year-old-hack-disinterred/ and construction techniques: https://entertaininghacks.wordpress.com/2015/02/21/vintage-hacking-or-the-past-is-a-foreign-country-they-do-things-differently-there/

Blah, it uses one of those new-fangled integrated clock chips, sacrilege!

[Delta]

Great video Dave.  I'm off upstairs to fire up the soldering iron! 😀

[Cliff Matthews]

Doesn't seem to be a 16-pin TTL version of the 4026, and the obsolete 24-pin 74143 would be pricey by now. Always loved the forward thinking of the 4000-series designs.

[SeanB]

IIL clock chips are nice, just that they run hot enough to cook on, and if the power fails battery life ( off that 9V battery they support) is only good for a few hours before it dies. CMOS will run for weeks off a coin cell, and I did hack in a LCD clock mechanism ( used the 32Hz backplane signal as a stable cheap clock source and a germanium transistor level translator because of the 0.5V swing it had) on one I did. 4V8 NiCd pack for backup with the display blanked, and the watch board was supplied using a simple resistor divider to give it 1V5 at the 100uA it needed. Selected resistors on test to get voltage to 1V5, just to get the value high.

Tossed it out a few years ago in a move. Sometimes I regret things.......

[SeanB]

Doesn't seem to be a 16-pin TTL version of the 4026, and the obsolete 24-pin 74143 would be pricey by now. Always loved the forward thinking of the 4000-series designs.

A lot of those designers were scratching their own itches, and designed stuff that solved problems they has come to experience, or that friends had experienced. That is why you had so many counters, especially the large number of ripple counters and the BCD dual ones.

[alexanderbrevig]

I love this video! Makes me want to throw out the µCU and try to get my hands dirty with CMOS

[asgard]

All well and good, Dave.  Righteous clock design.  However, I must call bullshit on the Ahmed bandwagon.  Here are the updated facts and context:

1.  Ahmed did not design that "clock" from scratch.  It was an existing Radio Shack clock removed from its enclosure and remounted into a briefcase.
2.  The clock was altered into a countdown timer, rather than an RTC.
3.  Said clock/timer was executing an active countdown when the incident occurred.
4.  The entirety of the situation resembled nothing more than an improvised explosive detonator being taken into a public school.
5.  Ahmed Mohamed's father, instead of consulting with the school board (which is the legal and responsive authority on this matter), has contacted CAIR, which is in the process of manufacturing a racial incident out of this event.
6.  The same father, a known jihadist, has twice ran campaigns for the presidency of Sudan, which last I checked, is not known as a wellspring of democracy but is known for impressing children into suicide bombers, as part of President Bashir's policy of global jihad and arms supply to Hamas and Hizbullah.

[AF6LJ]

All well and good, Dave.  Righteous clock design.  However, I must call bullshit on the Ahmed bandwagon.  Here are the updated facts and context:

1.  Ahmed did not design that "clock" from scratch.  It was an existing Radio Shack clock removed from its enclosure and remounted into a briefcase.
2.  The clock was altered into a countdown timer, rather than an RTC.
3.  Said clock/timer was executing an active countdown when the incident occurred.
4.  The entirety of the situation resembled nothing more than an improvised explosive detonator being taken into a public school.
5.  Ahmed Mohamed's father, instead of consulting with the school board (which is the legal and responsive authority on this matter), has contacted CAIR, which is in the process of manufacturing a racial incident out of this event.
6.  The same father, a known jihadist, has twice ran campaigns for the presidency of Sudan, which last I checked, is not known as a wellspring of democracy but is known for impressing children into suicide bombers, as part of President Bashir's policy of global jihad and arms supply to Hamas and Hizbullah.

Good Job, all factual.
I love it when someone posts the truth in such a concise form. 

[Delta]

Modified to be a countdown timer? Where did you read that?  From what I've seen, that sounds far above the young man's abilities...

[neotesla]

Get off of it, he's just a kid.

Geez... fighting the war on terror even here.

[Svuppe]

Ahh, that clock brings back memories.
I made one out of CD40192's back in my youth. They could count in both directions, and had a preset input so I could make it go from 00 to 59 when counting down (instead of 00 to 99).