A piece of art.
Casio-F-91W die-shot
131–140 of 167 posts
Re: Casio-F-91W die-shot
#132Re: Casio-F-91W die-shot
#133I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?
Almost all quartz watches have a similiar movement, running of a 32kHz crystal. Those give you about 15s/month accuracy, which is an oder of magnitude better than most mechanical watches and that for a very few bucks. More precise quartz watches exists, but they require quite a bit more effort, which of course translates into costs. Actually one of the earliest quartz watches on the market from Omega used a 2MHz crys…
To add to this—I’d say that watches are quasi-temperature-controlled. You wear the watch in varying conditions, but most people spend most of their time in controlled environments, and the watch is directly next to your body, which itself is temperature-regulated. This just means that temperature drift may be less of a factor for watches than it might be for, say, a clock on the wall or in a car.
Assuming you wear the watch.
Re: Casio-F-91W die-shot
#134Earlier quoted context omitted.
I was surprised by this inaccuracy too. But was impressed when I learnt that there is no analog wristwatch that can match this accuracy - they are all far far worse. (Isn't it shocking that all those super-expensive Rolexes and whatnot are all going off by minutes per month!) Get one of the Casio watches that syncs to atomic clock radio signals every night - it will be second-accurate all the time.
> But was impressed when I learnt that there is no analog wristwatch that can match this accuracy Seiko 5 automatics apparently[1] can.[2] [1] https://www.watchuseek.com/threads/seiko-5-is-pretty-accurat... [2] https://qr.ae/prvf6L
According to the linked thread, the Seiko 5 is an order of magnitude worse… 5 seconds per day, versus 15 seconds per month for a quartz watch.
Re: Casio-F-91W die-shot
#135Earlier quoted context omitted.
Get a Casio G-Shock. The 800 models can sync with your phone and the time is auto corrected. I bought a GBA-800 from a pawn broker - out of the dozen or so watches in my box it's the one I reach for if I have to know what time it is accurately.
One of my best bang-for-the-buck purchases was a Casio Waveceptor watch with a hybrid clock face. The watch uses the WWVB signal for nightly syncing. However, living on the East Coast means syncing is very dependent on day-to-day atmospheric propagation. When I visit more inland, it works great. The watch face is solar powered, so I’ve never had to change the battery. It has since been retired after 8 years of use fo…
I love my cheap waveceptor which is always, always accurate.
Actually in the process of choosing a casio lineage (waveceptor movement, metal case, sapphire crystal) - do I get titanium or blacked out stainless steel, lol
Re: Casio-F-91W die-shot
#136I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?
Almost all quartz watches have a similiar movement, running of a 32kHz crystal. Those give you about 15s/month accuracy, which is an oder of magnitude better than most mechanical watches and that for a very few bucks. More precise quartz watches exists, but they require quite a bit more effort, which of course translates into costs. Actually one of the earliest quartz watches on the market from Omega used a 2MHz crys…
Indeed, another challenge is crystal aging. For example, PCF2129 has an aging offset register. These devices are rated to +-3ppm over the huge range of -30-80C but the register allows for -7 to 8ppm offsets, if necessary.
Re: Casio-F-91W die-shot
#137I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?
The functionality of the F-91W is simple enough that I don't think a CPU would even be needed. Probably the digital parts of this chip are just state machines. That being said, the left half of the die shot looks like some kind of gigantic ROM, which could either be used by a CPU (as static program memory) or just transition logic/data for any generic state machine(s). Verilog came out in 1984, but its use for synthe…
vhdl started as a project to document integrated circuits. The department of defense was getting a lot, and more complicated, integrated circuits and wanted a standard to document the functionality. At some point someone thought, "you know, if the documentation is good enough we could reverse it and synthesize a circuit from it", and thus why you use vhdl(or more likely verilog) to program your fpga.
The two languages fill the same role in the ecosystem, I have to say that I have never used ether, but my impression is that vhdl has clearer syntax(if you can stomach it's ada look and feel) and verilog has better tooling. which makes sense considering that one was a documentation project and the other was an internal tool for simulation that escaped into the wild.
Re: Casio-F-91W die-shot
#138Earlier quoted context omitted.
Yes. I ended up buying a GWM5610 which synchronises through radio. It's cool. But still I would have hoped there would be a better "local" (i.e. self-reliant) solution.
There's software for the Beaglebone PRU so you can generate your own WWV signal, for receivers buried too deep into buildings or otherwise suffering from poor signal. Of course, with any HackRF you can also generate GPS signals. But it would be a lot less necessary if the watches had reasonable temperature compensation. Obviously the crystal frequency shifts with temperature, and they're typically adjusted to achieve…
Nxp sells a PCF2131 with an internal TCXO that runs on 64 nanoamps when not doing anything else. So with a modern CMOS process, the TCXO itself is not a big deal. A clock pin at 32768 cyc/s looks to be way more power hungry, which tells us that an ideal low-power solution is an all-in-one SoC.
Re: Casio-F-91W die-shot
#139Have a look at this. Joey built a whole swathe of sensors to plug in to a f-91W like circuit.
https://hackaday.com/2022/02/24/remoticon-2021-joey-castillo...
Re: Casio-F-91W die-shot
#140Earlier quoted context omitted.
At around 1976-1977 I bought one of those fancy new LED wristwatches, where you pressed a button and the time lit up in red. Straight out of James Bond, as I recall. As I was studying electronics at the time I brought the watch to the lab and opened it and connected a frequency counter to the oscillator, you could clearly see the crystal and a little trimming pot (I don't remember by now if that was a pot or somethin…
> and the bus is there exactly on time So that would locate you pretty unambiguously in Switzerland then?
Heh no :-) - because the railway stations here don't have station clocks with second hands, unlike Switzerland.. heck I don't know why they bother with the minute hand.