EEVblog #801 - How To Design A Digital Clock

[LabSpokane]

Really cool clock Dave!

Clever using the mains frequency as clock, love the discrete diode/transistor logic and the 0.1 second display was a nice touch!

I read once that utility companies used to adjust the number of cycles during the day for the benefit of clocks like this.

Anybody knows if this is true?

True.  Using the mains frequency as a clock synchronizer is how clocks kept time for decades.  And the number of cycles was adjusted mainly as an efficiency and power plant capacity issue.  The frequency would slow down during the day as the load increased, then it would be correspondingly sped up at night so that each day would have the same number of mains frequency cycles. 

BPA, I believe, did a test recently to see how many systems were still dependent on mains synchronization for timing.  The answer was: not many.  They may actually allow the mains frequency counts to vary from day to day in the future.  You would need to check with the operators of your particular power grid to know how they are handling this now. 

[LabSpokane]

And could I request that everyone just shut up about the whole Ahmed situation now?  That is just going nowhere. 

This thread is about building a clock.  And that's something really damned cool - and a very accessible, basic-building block project for a lot of interested electronics folks. 

[SeanB]

Used to be true, but now most have decided that they will allow a certain number of cycles slippage with heavy load and will not recover them at night with low load. You might be lucky in that you only lose a few seconds per month, but they pretty much decided it was too expensive to get the controllers to aim for midnight on the master clock to agree with UTC.

[Macbeth]

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

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.

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

Me too. This is great. Of course I am assuming you septics just using the kind of sardonic humour us limeys are known for? 

I mean as that great American John McEnroe stated "You cannot be serious!?"

As for Achmed, I think all of us and the media should just forget about it, at least until we find teachers being sacked for political correctness reasons or some other outrage. Dave closed the last thread, so I don't know why he effectively started another.

[Dinsdale]

Yeah, that clock is the bomb, Dave.

[Macbeth]

Used to be true, but now most have decided that they will allow a certain number of cycles slippage with heavy load and will not recover them at night with low load. You might be lucky in that you only lose a few seconds per month, but they pretty much decided it was too expensive to get the controllers to aim for midnight on the master clock to agree with UTC.

Kitchen clocks all used to run on the mains to keep time in the UK, but then cheap batteries and 32.768kHz crystals took over. Later we had accurate clocks using radio broadcasts for synchronisation. Now it's NTP.

[Howardlong]

And could I request that everyone just shut up about the whole Ahmed situation now?  That is just going nowhere. 

This thread is about building a clock.  And that's something really damned cool - and a very accessible, basic-building block project for a lot of interested electronics folks.

+1. Thank you.

[alien_douglas]

Great clock Dave.

I never ever made a clock. I did make frequency counter that did look very similar in construction to your clock.
I love veroboard 

Great stashes of old components, brings back memories.
My first ever job was as an electronics service engineer for IBM. I also collected many 7400 series chips from old faulty boards. The big problem was that IBM used to part number almost everything back in the eighties.
Although it may have been a standard TI 7401 TTL chip it would only have an IBM part number on it.  I could never remember all the IBM seven digit part numbers so a translation list was a must.

And yes, everything was part numbered especially for IBM, from SnapOn tools to Tektronics scopes.

And my favourite CMOS chip that I used everywhere was the 4017 (Not the 4026. Sorry Dave.)
I used to make blinky LED lights for my scale model projects. 4017 rocks...

Alien

[tggzzz]

I read once that utility companies used to adjust the number of cycles during the day for the benefit of clocks like this.

Not quite. For many decades non-clockwork clocks used the mains frequency as the time reference. LED digital clocks were a latecomer.

I believe that the average frequency is still required to be 50Hz. IIRC there are some moves to remove that restriction - not least because we are down to about a 2% capacity margin. Why? Due to the total failure of the market (with the complicity of government) to provide adequate generating capacity.

[tggzzz]

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!

Well, at that time TTL was very new, very expensive[1] and required an "accurate" 5V supply - all of which was a problem for an impecunious youngster.

[1] especially 7447s, looking at the adverts in http://www.americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1973-02.pdf

[g0hjq]

My first major project was a TTL digital clock, built during the school summer holidays in 1977. It used a 4:12 decoder and a diode matrix for the 12 hours display.

More recently, I've just finished building a kit using discrete Diodes/Tranistor logic with around 200 transistors, 500 diodes and no ICs. http://www.transistorclock.com

[Howardlong]

My first major project was a TTL digital clock, built during the school summer holidays in 1977. It used a 4:12 decoder and a diode matrix for the 12 hours display.

More recently, I've just finished building a kit using discrete Diodes/Tranistor logic with around 200 transistors, 500 diodes and no ICs. http://www.transistorclock.com

Beautiful. Pornographic even.

[Macbeth]

[1] especially 7447s, looking at the adverts in http://www.americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1973-02.pdf

Oh wow, I love going through old magazines... Page a16 "Candles are for eskimos" totally takes me back to the 70's, I can't remember a time when the 'leccy wasn't cut. The UK was worse than North Korea at the time. Though I think it wasn't just the national strikes but my parents being out of work and out of 50p's shillings for the meter just as often. I totally remember the candles. It's also why I loved my crystal set. Those Ever-Ready batteries never lasted more than 5 minutes 

ETA: The 50p's were for the, can you believe it, pay-slot colour TV. I preferred the black and white because we could have that on any time. To use the colour we had to put 50p in the slot and wind a dial and then it would tick away...  Oh fuck, life was grim in the '70s...

[EEVblog]

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.

For the 1 millionth time, everyone knows this. It was bleedingly obvious to anyone with electronics knowledge who saw that photo.
So what? Beginners have to start somewhere, many of us were in the exact same position.

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.

I call bullshit. Provide proof.
Exactly how do you modify a commercial clock chip to down?
Please be precise and technical in your answer.
Because if experiences electronics people don't know how to do it, I'm pretty sure Ahmed, who is clearly a rank beginner has no clue how to do that.

[EEVblog]

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. 

Crap job, reposting bullshit (consisting of lies mixed with some real information) found in sewers of internet.

We all are entitled to our opinion.
One thing you and I have in common, we were not there to witness any of the facts.

There is no need for opinion, this is purely a technical question. Please explain how a commercial desk clock chip can be modified into a countdown timer.

[EEVblog]

Dave, did you not use PNPs at the time?

Sure, but NPN's worked just fine.

[LabSpokane]

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.

For the 1 millionth time, everyone knows this. It was bleedingly obvious to anyone with electronics knowledge who saw that photo.
So what? Beginners have to start somewhere, many of us were in the exact same position.

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.

I call bullshit. Provide proof.
Exactly how do you modify a commercial clock chip to down?
Please be precise and technical in your answer.
Because if experiences electronics people don't know how to do it, I'm pretty sure Ahmed, who is clearly a rank beginner has no clue how to do that.

Picture help:


http://www.ebay.com/itm/Micronta-Vintage-Digital-Alarm-Clock-with-Large-Red-Display-63-765A-/271992316574?hash=item3f5401629e

Buy this clock for over $150 and prove Dave and common sense wrong. 

[EEVblog]

We do tend to use what we cut our teeth on.
Dave made a comment regarding microcontrollers in the video. We actually had the 8031 and the 8051 before 1980.

Yes, but almost no one in the hobby field used micro's until basically the PIC16C84 came out in 1993 (no flash parts then).
It was not a cheap or easy field to get into like it is now.

[EEVblog]

How do you adjust that clock?
If it's all BCD overflow logic, does that mean you have to run to every 10th of a second to get to the right time?

By very careful fast forwarding.

[Macbeth]

There is no need for opinion, this is purely a technical question. Please explain how a commercial desk clock chip can be modified into a countdown timer.

Especially by a lad who clearly doesn't know one end of a soldering iron from the other. I mean it doesn't work both ways. He's either a rank amateur who knows how to twiddle a screwdriver, or a genius bomb-maker who goes to the extreme of reverse engineering a fucking radio alarm clock instead of going with a much simpler 555 timer or Arduino or the good old mechanical switch on the minute hand trick... In fact I remember using potassium permangate and glycerine as a fuse - no electronics or mechanics needed.

[EEVblog]

http://www.ebay.com/itm/Micronta-Vintage-Digital-Alarm-Clock-with-Large-Red-Display-63-765A-/271992316574?hash=item3f5401629e
Buy this clock for over $150 and prove Dave and common sense wrong.

As always, I'm happy to be proven wrong.
It might very well have a countdown timer in it, but can't say I've ever seen one.
And if it does require some form of technical hack to do it (no evidence of in photo), then Ahmed has much better skills then it seems half the world is shooting him down in flames for lack of.

[EEVblog]

More recently, I've just finished building a kit using discrete Diodes/Tranistor logic with around 200 transistors, 500 diodes and no ICs. http://www.transistorclock.com

Wow, very nice! 

[Deathwish]

[1] especially 7447s, looking at the adverts in http://www.americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1973-02.pdf

Oh wow, I love going through old magazines... Page a16 "Candles are for eskimos" totally takes me back to the 70's, I can't remember a time when the 'leccy wasn't cut. The UK was worse than North Korea at the time. Though I think it wasn't just the national strikes but my parents being out of work and out of 50p's shillings for the meter just as often. I totally remember the candles. It's also why I loved my crystal set. Those Ever-Ready batteries never lasted more than 5 minutes 

ETA: The 50p's were for the, can you believe it, pay-slot colour TV. I preferred the black and white because we could have that on any time. To use the colour we had to put 50p in the slot and wind a dial and then it would tick away...  Oh fuck, life was grim in the '70s...

You must of lived next door to me !. ditto

[tggzzz]

[1] especially 7447s, looking at the adverts in http://www.americanradiohistory.com/Archive-Wireless-World/70s/Wireless-World-1973-02.pdf

Oh wow, I love going through old magazines... Page a16 "Candles are for eskimos" totally takes me back to the 70's, I can't remember a time when the 'leccy wasn't cut. The UK was worse than North Korea at the time.

I still keep candles, and have very occasionally used them.

I'll stock up next year, before the lights go out again - this time because we don't have the generating capacity. See https://www.ofgem.gov.uk/publications-and-updates/security-electricity-supply-faqs and read between the lines Or maybe the domestic lights won't go out, because the businesses on cheap rates will get "load shedded".

Though I think it wasn't just the national strikes but my parents being out of work and out of 50p's shillings for the meter just as often. I totally remember the candles. It's also why I loved my crystal set. Those Ever-Ready batteries never lasted more than 5 minutes 

ETA: The 50p's were for the, can you believe it, pay-slot colour TV. I preferred the black and white because we could have that on any time. To use the colour we had to put 50p in the slot and wind a dial and then it would tick away...  Oh fuck, life was grim in the '70s...

Some things were better (e.g chemistry lessons), some weren't (e.g. bicycle lights).

[kwass]

Yes, but almost no one in the hobby field used micro's until basically the PIC16C84 came out in 1993 (no flash parts then).
It was not a cheap or easy field to get into like it is now.

Maybe not that cheap but it was easy ... mostly becasue of Digikey (not sure if they sold outside of the US back then).

There was the INS8073 chip and development board.  The INS8073 had NSC Tiny Basic built in and the development board that Digikey sold (can't remember the model number of this)  provided the hardware for writing tokenized BASIC programs directly to EPROM. 
http://www.classiccmp.org/cini/pdf/NatSemi/INS8073_DataSheet.pdf

You didn't need anything more than a dumb terminal and simple power supply to start using this micro for projects.  It was on the expensive side but I made a few projects with them.  This was was back in 1981, way before the PIC and the BASIC Stamp, etc..  There were a few other single chip/development boards too that were targeted for hobbyists.

Back then and well before that, Digikey was only a hobbyist company.  They started off selling surplus electronics via a typewritten and hand drawn 8 page catalog.  Later they sold a lot of NSC clock modules and PCB kits to "make your own".  I used to make those to order for my family and friends, there were lots of options to pick from on these modules: alarms, temperature display, date display, etc..  Digikey had interesting stuff before they started selling to the industry.