how to build a clock with pulse for the hours!

Pinholed comdoms.

a.k.a. Morse code. It's rather ironic that it disappeared into obsolescence around the same time that everything has become digital.

That's the advantage of the phone-dial system. Replace the button with a photodiode plus a disc with 10 holes; the uC interface is the same, but it's simpler for the user. I had originally thought of a safe-style combination lock, but that requires two pins for quadrature encoding.

What's your beef, exactly?

AFAICT, the 12F508 is the cheapest model which can drive an external crystal.

I said it only *needs* one pin on the uC.

Again, what's your beef, exactly? If you think there's a technical problem, maybe you should state it rather than just spewing ad-hominem attacks.

FWIW, I find this problem interesting as it mirrors a common issue in software development, namely that the code to provide the user interface is often an order of magnitude more complex than the code it's interfacing to.

The problem with wire wrapped around the hour hand is mechanical - these modern quartz clocks have pressed on hands that have almost no torque before the hand slips or twists. The old "baby ben" mechanical alarm clocks could be used that way - sturdy hands and good mechanical connection.

I suspect the only bomb designers (assuming the wire wrapped hand idea came from seeing it on TV) are in Hollywood. Today, its lots easier to just use the mechanical switch they use for the alarm to work the ignition circuit for a bomb and that relies on a cam - but it wouldn't be too obvious to the casual TV viewer like the wrapped hands or digital count down timer.

The reason I know. Quartz analog clocks are a cheap and dirty way to make "totalizing" meters. Want a cheap watt-hour meter that holds its totals when power is removed? Quartz clocks can't be beat. But I had to destroy several in the process of learning. The only difference between the $30 "made in China" quartz alarm clock and the $1 one, is the price tag and the external plastic it comes with.

The pulse output (using the WW hand idea) from a long contact could easily be done with an electrolytic cap with a resistor across it in series with the contact output. Cap charges and outputs amps for a few milliseconds then has an hour to discharge once the contact opens.

Interesting unrelated floobydust: the stepper motor they use is driven from an H-bridge inside the glob of epoxy - each second is alternating polarity output to a single coil - the pole magnet shape determine the direction it goes in.

Ditto that. But its a pain in the ass way of inputting data or reading data. Easier to use Morse code in my opinion - save the fact that you only are dealing with numerical data here. Easier to use BCD maybe. Other than the bragging rights to being the only one able to reset the clock - I'd stick with a very easily understood technique.

You can "Charlieplex" twelve output bits from just four lines of a tri state pic for a LED display . . .

No good deed and all that, John.

Jon

P.S. Since I just started using this new-fanged (free) usenet site to access ABSE, I've not seen your post showing up there. (Before using it, I simply didn't have ANY access to ABSE because Verizon killed all alt.* newsgroups, many many months ago.) So I couldn't look before and can't seem to look now. That link you gave just came up 'not found' when I fed it to Agent to go grab from this free usenet service. And when I grab 'all headers' it still doesn't show up. I'm not happy about that as I assume it is up there and you see it just fine. Bugs me that it isn't coming up on my end.

While waiting for comments, how about adding transformerless line powering together with the AC zero-cross detection circuit? Design in specific component values. Might as well finish the job, since you are assuming US 60Hz available (reasonable.) :)

Jon

JF's circuit has been there for a day or more now.

What Usenet service are you using?

Teranews seems to work reasonably and has less than $10 once only setup charge.

John G.

I just tried a couple of free servers: freenews.netfront.net and news.teleportsv.net. Beyond Verizon, which has completely dumped all alt.* newsgroups in a single breath, I haven't taken the trouble yet to commit myself to a for-fee service. Still deciding just how badly I want access to alt.*, I suppose. So far, the only reason is for alt.binaries.schematics.electronic and that isn't a good enough reason by itself to start paying fees.

Jon