Any way to make LEDs mimic analog seconds movement on a clock?

May 19, 2005 24 Replies
R

I've done some more looking at this, and seriously, modifying the PIC program and modifying your segment driver matrix is about the only practical way I can think of to do this, short of the 60-bit shift register. The problem is that the seconds digits are multiplexed in with all of the other digits.

You could use a couple of latches to capture the individual segments, and then run them into a 14 x 60 diode matrix - actually, you don't need all 14 inputs - of the 7-segment patterns, there's some redundancy that can be treated as "don't care" - and kinda build a ROM out of diodes, and run your 60 dots from it.

Like I said, if it were me, I'd find a way to hack the PIC program.

Take a look at that roulette wheel link that someone else posted - it couldnt hurt!

Good Luck! Rich

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F

I would forget the 7219 and use two M74HC42 available from Mouser. The

74HC42 are BCD to decimal decoders which means you input a 4-bit BCD code in the range 0-9 and it activates 1 of 10 outputs low. So you arrange the 60 LEDs into 6 groups of 10, use the MSD of the clock seconds for input to one 74HC42 to select one group of 10 LEDs, and then the clock LSD inputs to the second HC42 to select the 1 of 10 LEDs in the group. This requires 2x 16-pin 74HC42, one current limiting resistor, and six cheap transistor+ base resistor like so- how you extract the seconds MSD and LSD depends on what's in the clock:

View in a fixed-width font such as Courier.

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R

Way.

1 ea. 32768 Hz watch crystal, 1 ea. 4020/4040/4060, 8 ea 74HC164, 8 ea. R-paks, 60 ea. LED. Maybe one or two logic gates - you could, theoretically, sync it up to second 00, but that's a little more decoding logic. Or a program hack and PIC output pin.

Do the seconds ring entirely independently of the PIC clock. Since you've said you're going to omit the seconds digits, who's going to notice whether they're exactly sync'd? Somebody looks at the clock, it's

7:24 and the seconds dot is at 18. They look at the clock again, it says 7:25 and the seconds dot is at 46. Who cares? If they confront you about it, blame me. "Some weird guy on the internet gave me the design, and said I should call it a _feature_!"

Trust me, this is the simplest no-programming hardware solution that anyone is going to come up with at what we're getting paid around here. ;-)

Good Luck! Rich

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F

The last two digits to go away, then add the roulette wheel, as you say, run off the seconds digits logic. Or if possible, program this into the PIC--unfortunately like Steve Ciarcia say's "My favorite programming language is solder"

I'll need to absorb all these great suggestions. Thanks for your patients.

No way. Largo

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L

This is what originally thought--do it independently and here's how. Another circuit using an Atmel 8051 varient chip which I think code is easier to hack. Now there's two microcontrollers in my digital clock but maybe the image found on:

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and circuit at:
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could do the trick. I'd still like the LEDs to start at the 12 O-clock point when the seconds digits are "00".

Thanks for the great pointers.

Largo

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