Is it possible to make a gate level digital wrist watch

[Fluffyboii]

Hi,
Ever since I designed and simulated a digital watch with logic gates for one of my electronics classes in university I had this urge to take that design and make it reality with only transistors. Not even logic gates or flip flops. I did find that it is already done my different individuals and it is not an easy feat.

Anyway I am super into digital watches for the past year or so. I simply like telling the precise time at a simple glance and I love the unusual shape and sizes some digital watches have. Today the idea of making my own digital wrist watch got stuck on my mind. Obviously the easiest way to do it would be to get a microprocessor, few small 8 bit displays, rtc module for precise time keeping, slamming all of that in a 3d printed case. Even doing that would be a feat in itself.
Unfortunately using something like an Arduino, taking the Atmega something processor from it feels wrong. People make smartwatches with lots of functionality with those and just simple time keeping with it would make me sad. I could get a less powerful microprocessor and try to code in assembly to torture myself but I am not in that mood.
Using transistor level logic would never fit in a wrist watch form factor, I wonder if using smd versions of logic gate chips, flip flops, multiplexers, etc. would make it possible to fit in a wrist watch or do I need to get counter ICs and other more complex ICs for it to fit. Today most wrist watches that are digital have a small mcu, a quartz crystal with an inductor, few caps and resistors and thats it. Pretty boring and unrepairable.

I am also curious about when something stops being analog. Analog circuits are fascinating. I also want to make a calculator with all solid state components but analog in design. Adding and subtracting with op amps is easy enough but multiplication is difficult Obviously having it all solid state requires using some kind if led display which requires a dac at some point. Can something similar be done with a watch, nearly fully analog except the display. This is bit off topic from my initial wrist watch idea but is it possible to make a watch with a led display that does all the time keeping with an analog circuitry, just for the sake of it. Something like a RC circuit that charges a capacitor until a voltage threshold is passed that the triggers a comparator for example to keep time. I never truly understood when some circuit truly becomes digital.

This is just my random thoughts at 5am.
Edit: I just searched bit more and a microprocessor less watch requires immense amount of logic elements just as I remember that will definitely not fit in a small package unless I use ICs to do most of the hard work.

 

[rjenkinsgb]

Digital means the voltage no longer represents a varying value; just above or below some level for 1 or 0.

Watches, or at leas unusual ones, are one of my side hobbies..
I have a "Sinclair Black Watch" I built from a kit, when they first came out; that has a four digit LED display driven by a custom designed IC.


It's definitely possible to use logic ICs, a combination of divide by six and divide by two, or ten, to get /12 or /60.

However it works, to keep accurate time, it needs a frequency reference of some sort, and for electronics, the simplest solution is a quartz crystal oscillator. 32.768 KHz is the commonest standard for timekeeping.
A 15 stage divider takes that down to 1Hz.

To use analog methods, you would need to go from digital to analog, then convert back to digital again for display??

(I can imagine a clock using voltmeters with numbered scales at the time display!)

There are many other options for clocks, some of which can be used to make oversize "wrist watch" devices - Nixie tube ones are quite a common variation. You could even use Decatron tubes for a big clock display..

Nixie Watch, Titanium, Self Made With Accelerometer, Made in Italy - Etsy UK

This Pocket Watches item by TITANTIMEPIECE has 31 favorites from Etsy shoppers. Ships from Italy. Listed on 14 Feb, 2024

www.etsy.com

Nixoid | Online store

Nixoid Store was founded in 2017 with the vision of building the best online store specializing in nixie tube wrist watches. Free shipping worldwide.

nixoid.store

Synchro resolvers driving the hands would be another odd one, that would be a kind of analog controlled display.


For info, the very first electronic watches used a single transistor and an analog oscillator, in conjunction with a "tuning fork" mechanical resonator for the frequency standard - the Bulova "Accutron" series from the 1970s. I have a couple of different models in my little collection.

More info below. If you look at the photo, the fixed base of the tuning fork is just visible at the bottom edge of the movement & the tops of the vibrating arms have the "cups" that fit around the drive and feedback coils. They hum rather than tick, at 360Hz. One arm of the fork has a tiny ratchet pawl that pushes round a wheel with microscopic teeth, to drive the mechanics.

Bulova Accutron [Watch Wiki]

www.watch-wiki.net

Long before those, there were "Master clocks" - typically a pendulum clock with electromagnetic system to keep it running and give a pulse of power on a pair of wires at regular intervals.

Those connected to slave clocks, that just had a solenoid to drive the mechanism through a ratchet.

As long as everything worked as it should all the slaves would show exactly the same time as the master. They were common in big factories and offices etc. from around 1900 onward, until electronic clocks took over.

Master clock - Wikipedia

en.wikipedia.org

 

[Fluffyboii]

Digital means the voltage no longer represents a varying value; just above or below some level for 1 or 0.

Watches, or at leas unusual ones, are one of my side hobbies..
I have a "Sinclair Black Watch" I built from a kit, when they first came out; that has a four digit LED display driven by a custom designed IC.


It's definitely possible to use logic ICs, a combination of divide by six and divide by two, or ten, to get /12 or /60.

However it works, to keep accurate time, it needs a frequency reference of some sort, and for electronics, the simplest solution is a quartz crystal oscillator. 32.768 KHz is the commonest standard for timekeeping.
A 15 stage divider takes that down to 1Hz.

To use analog methods, you would need to go from digital to analog, then convert back to digital again for display??

(I can imagine a clock using voltmeters with numbered scales at the time display!)

There are many other options for clocks, some of which can be used to make oversize "wrist watch" devices - Nixie tube ones are quite a common variation. You could even use Decatron tubes for a big clock display..

Nixie Watch, Titanium, Self Made With Accelerometer, Made in Italy - Etsy UK

This Pocket Watches item by TITANTIMEPIECE has 31 favorites from Etsy shoppers. Ships from Italy. Listed on 14 Feb, 2024

www.etsy.com

Nixoid | Online store

Nixoid Store was founded in 2017 with the vision of building the best online store specializing in nixie tube wrist watches. Free shipping worldwide.

nixoid.store

Synchro resolvers driving the hands would be another odd one, that would be a kind of analog controlled display.


For info, the very first electronic watches used a single transistor and an analog oscillator, in conjunction with a "tuning fork" mechanical resonator for the frequency standard - the Bulova "Accutron" series from the 1970s. I have a couple of different models in my little collection.

More info below. If you look at the photo, the fixed base of the tuning fork is just visible at the bottom edge of the movement & the tops of the vibrating arms have the "cups" that fit around the drive and feedback coils. They hum rather than tick, at 360Hz. One arm of the fork has a tiny ratchet pawl that pushes round a wheel with microscopic teeth, to drive the mechanics.

Bulova Accutron [Watch Wiki]

www.watch-wiki.net

Long before those, there were "Master clocks" - typically a pendulum clock with electromagnetic system to keep it running and give a pulse of power on a pair of wires at regular intervals.

Those connected to slave clocks, that just had a solenoid to drive the mechanism through a ratchet.

As long as everything worked as it should all the slaves would show exactly the same time as the master. They were common in big factories and offices etc. from around 1900 onward, until electronic clocks took over.

Master clock - Wikipedia

en.wikipedia.org

Thanks for telling about all of this. I love the idea of a nixie tube watch, they look lovely. Would definitely try to make one if I could source small nixie tubes. I also love early red LEDs that are in some old Texas Instrument calculators and VFDs also look awesome. But all of those options are hard to get and in case of nixie tubes hard to drive as well since they require like 170V supply if I remember correctly. I found these small lcd displays for 3d printing pens. It sucks that they are 3 digits instead of 4 but I am thinking I may just use two of them side to side and ignore the most left and right digits or use them for seconds. Using a quartz oscillator then dividing the clock down to 1hz to use with counters seems to be optimal solution since I do not want it to be too large. I will check some schematics of this kind of watch I guess.

 

[danadak]

If you can link to source of the 3 digit displays ?

Regards, Dana.

 

[Fluffyboii]

If you can link to source of the 3 digit displays ?

Regards, Dana.

They are the first to pop out when I search “small display” on aliexpress.

 

[danadak]

I see there is not data sheet for them, are they direct static drive ?

As an aside I searched on your “small display” and waded thru many pages,
finally fooled around with "small lcd display segment 3 digit" and found them.
I thinks its algorithms of my prior search's, large graphic displays, that
cause the problem. We users being screened on adaptive algorithms, its a
new world. Thanks for the reply.

Regards, Dana.

 

[Fluffyboii]

I see there is not data sheet for them, are they direct static drive ?

As an aside I searched on your “small display” and waded thru many pages,
finally fooled around with "small lcd display segment 3 digit" and found them.
I thinks its algorithms of my prior search's, large graphic displays, that
cause the problem. We users being screened on adaptive algorithms, its a
new world. Thanks for the reply.

Regards, Dana.

I did fix the link, apparently it was not functional the first time. Yes Aliexpress search is bit weird. I honestly don't know much about LCD displays. I found some images that at least says it works at 3V, looks like there is no datasheet. What does 1/4Duty and 1/3Bias mean for driving method? I was hoping I would be able to directly drive this with some series resistors connected to something like CD4026. A 14 bit binary ripple counter IC to divide a 32.768Khz clock down to 2Hz then 2 flip flops to make it 1Hz. There are accurate temperature compensated oscillators like DS32Khz but it seems like they are not sold locally so I would have to buy it from some random seller from China hoping they won’t send me a fake chip. Or could just buy a regular 32768Hz quartz crystal with CD4060 like it is done here. I would need 6 CD4026s, some AND gate ICs so I may keep the total IC count under 10. I think that it may be possible to cram everything in a wrist watch sized form factor with SMD components that way. I do think using separate counters, display drivers, etc would be cooler but I don't think it would fit in a small case considering the sheer amount of ICs used here.

If I can not make the watch with simpler components and must use CD4026s to do most of the work because of size and power consumption constrains I would at least want my watch to be more accurate than my fw-91 which skips a second about every week. Do you know any other way than to buy a special quartz crystal oscillator to get a very accurate clock signal. Would it still be possible to use a separate quartz crystal and build a circuit around it to correct temperature variations. Would it make sense to pursuit such accuracy for something silly like this?

 

[rjenkinsgb]

There is an article on them here:

3digit multiplexed LCD (custom) driver

Hello ! I am building for some time a cct to drive a 3digit multiplexed LCD. (from aliexpress) From the sellers on aliexpress I managed to find a circuit diagram of the LCD. I color it myself to understand exactly how to actually drive it. After making the cct in reality, I discovered that...

www.electriciansforums.net

The OP on that thread says they glitch - but I believe their code is trying to use DC drive?

"bare" LCDs must have an equal duty cycle AC signal, by inverting both the segment and common signals at equal intervals.

See page 12 of this for example waveforms, for a display with three commons:

https://www.mouser.com/datasheet/2/302/PCF8562-3139325.pdf

Some PICs have an LCD drive system built in, that can produce the correct multi-level waveforms, eg. PIC16LF19155 and similar.

 

[danadak]

Its a muxed drive then :

https://ww1.microchip.com/downloads/en/Appnotes/AN658-LCD-Fundamentals-and-the-LCD-Driver-Module-of-8-Bit-PIC-MCUs-00000658C.pdf

Regards, Dana.

 

[Fluffyboii]

There is an article on them here:

3digit multiplexed LCD (custom) driver

Hello ! I am building for some time a cct to drive a 3digit multiplexed LCD. (from aliexpress) From the sellers on aliexpress I managed to find a circuit diagram of the LCD. I color it myself to understand exactly how to actually drive it. After making the cct in reality, I discovered that...

www.electriciansforums.net

The OP on that thread says they glitch - but I believe their code is trying to use DC drive?

"bare" LCDs must have an equal duty cycle AC signal, by inverting both the segment and common signals at equal intervals.

See page 12 of this for example waveforms, for a display with three commons:

https://www.mouser.com/datasheet/2/302/PCF8562-3139325.pdf

Some PICs have an LCD drive system built in, that can produce the correct multi-level waveforms, eg. PIC16LF19155 and similar.

I did not know LCDs required special circuits to drive them. That explains why the modules used for Arduinos etc. have chips at their back.

 

[danadak]

Typical bias generation -

Note if you need all these counters and lcd bias controller and generation and A/D and OpAmps and DAC
and lots of counter, PWM, all on one chip........PSOC has all that stuff. Drag and drop, and config. Drivers
already done pretty much.

Regards, Dana

 

[rjenkinsgb]

One of these six digit glass LCDs would be more suitable - two separate 3 digits woudl be difficult to drive.

https://www.aliexpress.com/item/32324866141.html

Something like that should work directly from the PIC16F19155, and the combination is small enough and low enough power to make a practical battery operate watch.

 

[Fluffyboii]

One of these six digit glass LCDs would be more suitable - two separate 3 digits woudl be difficult to drive.

https://www.aliexpress.com/item/32324866141.html

Something like that should work directly from the PIC16F19155, and the combination is small enough and low enough power to make a practical battery operate watch.

Looks like using bare LCD is out of question then I don’t really want to use a microprocessor for the watch, I hate coding and I have no experience using PICs. Apparently there are 0.2 inc 7 segment LED displays but I was unable to find anything for sale smaller than 2.8 inc. I think those would be suitable to direct drive while still looking decent and being small enough.

 

[Nigel Goodwin]

Making a watch with dumb IC's is going to take a LOT of them, be very difficult and complicated, and be more of a grandfather clock than a watch. You need either a micro-controller or a custom clock chip.

As for the bare LCD displays, there are a few PIC's which include the required drive circuitry inside the PIC.

 

[Fluffyboii]

Making a watch with dumb IC's is going to take a LOT of them, be very difficult and complicated, and be more of a grandfather clock than a watch.

You are right. It is probably not possible to make something small with dumb ICs. What about CD4026 though, it combines a lot of functionality in a single package. Maybe I just build a normal sized watch with those since it is indeed probably not possible to cram like 6 of them and even more ICs in a wristwatch.

I may look into programming PIC's too I guess.

 

[Nigel Goodwin]

You are right. It is probably not possible to make something small with dumb ICs. What about CD4026 though, it combines a lot of functionality in a single package. Maybe I just build a normal sized watch with those since it is indeed probably not possible to cram like 6 of them and even more ICs in a wristwatch.

I may look into programming PIC's too I guess.

Don't forget, you need hours, minutes and seconds?, possibly date?, plus a method of setting the time - you're talking a LOT more than just one CD4026. With a PIC (or other processor) you're down to just a single chip that does everything, and most PIC's even have a TMR1 facility that runs from a 32KHz crystal, you simply set it to generate an interrupt every second, and the PIC spends almost all of it's time in sleep, drastically reducing current consumption.

Anyway, if not - have a look here:

DIY Discrete Logic Clock | Andrew Wilkie

Most digital clocks these days are made from microcontrollers, so I created a discrete logic clock without a microcontroller!

andrewwilkie.me

 

[DEMandell]

Another approach to designing the circuitry for a digital watch is to use a small FPGA. There are suitable parts available from Altera (MAX10 series, for example) and Lattice (iCE40UL series), among others, and there are free development tools available too. The parts can be purchased from the usual distributors, including relatively inexpensive development boards. The trickiest part will be assembling the hardware as these are only available in surface-mount packages, but designing PC boards is now much easier (and cheaper!) using software like KiCAD, and many PCB fab houses offer assembly services that can handle surface-mount parts, and will do small quantity prototype runs for not all that much money.

The nice thing about these small, low-power FPGAs is that you can pack a relatively large amount of logic into a small package, and it's programmable and hence upgradable as you improve your designs. The chips are generally programmed in a high-level hardware description language (HDL) such as Verilog or VHDL (my preferred language.) These HDLs look like software, but they require thinking about things a little differently since what you're really describing is a collection of logic that operates in parallel as if you had wired up a bunch of gates and flip-flops. There are lots of online references to creating logic designs using HDLs.

 

[Fluffyboii]

Another approach to designing the circuitry for a digital watch is to use a small FPGA. There are suitable parts available from Altera (MAX10 series, for example) and Lattice (iCE40UL series), among others, and there are free development tools available too. The parts can be purchased from the usual distributors, including relatively inexpensive development boards. The trickiest part will be assembling the hardware as these are only available in surface-mount packages, but designing PC boards is now much easier (and cheaper!) using software like KiCAD, and many PCB fab houses offer assembly services that can handle surface-mount parts, and will do small quantity prototype runs for not all that much money.

The nice thing about these small, low-power FPGAs is that you can pack a relatively large amount of logic into a small package, and it's programmable and hence upgradable as you improve your designs. The chips are generally programmed in a high-level hardware description language (HDL) such as Verilog or VHDL (my preferred language.) These HDLs look like software, but they require thinking about things a little differently since what you're really describing is a collection of logic that operates in parallel as if you had wired up a bunch of gates and flip-flops. There are lots of online references to creating logic designs using HDLs.

I had my fair share of Verilog, the boards we had in school had their software support ended for some reason by AMD and only worked with AMDs dead IDE software I forgot the name of that never worked properly. We also had a optional HDL class but many did not take it because many of my friends and I hated coding in Verilog as there were no ways to debug the code and stuff we wrote neither worked or flashed to the boards There is one friend of mine that actualy did his internship on FPGAs and he recently started working in the same company part time.

I could check FPGAs again, I guess using a more modern one could involve less suffering.

 

[Fluffyboii]

One of these six digit glass LCDs would be more suitable - two separate 3 digits woudl be difficult to drive.

https://www.aliexpress.com/item/32324866141.html

Something like that should work directly from the PIC16F19155, and the combination is small enough and low enough power to make a practical battery operate watch.

I do not know anything about PIC programming, seems like the go to option for programmer is pickit3 or 2. There is PIC K150 for much cheaper than those but seems like it wont program the PIC you mentioned. I also want to ask, is it worth it to learn using these when everyone is using AVR microprocessors that are more powerful and probably documented better.

I wish they still made this type of displays. I could probably find another calculator like this to steal the displays but it would be better to find something that is new.

I finally found some 0.2 inc LED displays for sale. Quite pricey though.

There are few cheap clock kits sold on Aliexpress that use AT89C2051. I wonder why they use that specific microprocessor.

​

 

[danadak]

This is going to sound easy because it is.

There is a group of part families that has not only standard HW but also
a fabric for more sophisticated "standard" HW and user designed HW
if you want your own custom component.

So easy path first, you drag and drop out of parts HW library various HW
pieces, anything from simple gates to dig filter and in between, like PWM's
with deadband, up/dwn counters, timer..... Then using a simple wire wizard tool
wire uop internally and out to pins the HW components. Note each of the
pics below of the HW is an internal component. Then dbl click component
and config its basic parameters. Last you write 1 line of code, a start f()
given to you as a part of each components SW lib, and you have an almost
codeless design running. Tool does all the timing verification for you, its rare
you have to do anything with that. I have worked with that twices in 12 years,
rare you have to mess with it. Also not below all the analog HW in chip.

For designs that need real time control of the component HW, each component
has a rich lib of f() calls to manipulate it, like change PWM duty cycle, read
a counter, etc.. You are not writing drivers per se, just high level application
code, like what do I do with my A/D or counter value.

3 families, 4M low end, 5LP high end, 6 dual core for blue tooth and cryoto work.

Here is specific example for recent design requirement, user needed 24 PWMs to drive
24 high power LEDs, to monitor each LEDs current. And to communicate to PC over
USBUART. This left a large amount of fabric and HW for other stuff available, like
display, encoder....One chip....

For more sophisticated users (the community) one can design their own onchip
component to add to the libs. User community has done CPLD, 74HC equivalents,
DDS.... I did a 64 bit SIPO shifter, 64 bit counter for proof of concept. Onchip compo-
nents can be done with schematic capture and or Verilog.

Board to use for projects with nominal I/O count ~$15, I use that 90% of the time.
CY8CKIT-059.

IDE (PSOC Creator) and compiler free. Used for 4, 5LP, 6. Also MODUS more for the 6.

For each family 100's of projects already done one can cut and past from. Users
have done everything from simple codeless logic designs to one chip oscilloscopes.

Here is an example I did for my own lab :

Test Bed DDS and WaveDAC burst tool

Occasionally I need to generate custom wave forms and burst a known number of cycles into a DUT. This is a single chip solution, board I typically I use is $ 10. You just drag and drop components onto schematic, wire internally with a wire wizard tool and out to pins, right click and config...

www.edaboard.com

Here are onchip components (multiple copies in most cases) :

PSOC available for >> 20 years (the old 1 family even longer) and most of these families.
Quite stable.


Regards, Dana.