Re: Adding 60 LEDs to digital clock to mimic second hand


Largo wrote:
On 24 Jun 2006 21:44:32 -0700, "Glenn Gundlach" <stratus46@xxxxxxxxx>
wrote:

Largo wrote:
For digital clock, I have a 3 to 8 decoder driving six common anode,
7-segment displays via PNP transistors. In a common scenario,
display
segments are strobed from 8 bits of the microchip pins. I have 220
Ohm resistors in series with each segment. Clock displays time
format
in "hh:mm:ss" where the minutes increment for each count "00 to 59".

I want to add 60 LEDs for mimicing a second hand moving around the
circle of a clock face. LEDs must be off at the 12 O-Clock
position,
then illuminiate one LED, two LED, etc. for each second all around
the
face each minute.

Aside from 60 LEDs, I thought adding or modifying the above circuit
with darlington transistors--it's base driven from the 8 bit port.
Plus connecting individual segments to the darlington collector
while
figuring which LED's cathode to connect, illuminate and remain lit
in
sequence for each cycle of the simulated minute.

Do I need to reprogram my PIC for this? Or is there some extra
decoder chips or whatnot I could use to create the desired LED
analog
effect?

Largo

I'm not sure what precisely you're attrempting. As I read it, you have
an operating 6 digit clock and you want to add a circle of 60 LEDs for
seconds.

will the seonds 7 segment still be running?
Yes.

Do you want 1 LED lit at a time?
Yes

In paragraph 2 you say no LEDs for 0 then ..... which
implies to me more than 1 LED lit meaning a sequential illuminating
ring. Is that it?

Yes. I wish create an all-LED digital clock with an analog sweep
seconds display and central 7-segment-digits display. The desired
effect and appearance to a broadcast universal clock like Leitch model
UDC-5212.

Basically you need 60 LED drives decoded from the
seconds counter. You suggested 2 4017 Johnson counters but you still
need to gate together the 20 outputs for the 60 LEDs. Pubudu suggested
shift registers which would need a 1 second clock pulse, data input and
reset/clear. With this you could do 1 LED/second or an advancing ring
if you like that better by setting or clearing the data input before
shifting. I vote for the shift registers
Which shift register chip do you suggest?

Or what about MAX7219? I'll have to reprogram my PIC and use three
spare pins. Or would spare pins from a CPLD do it?

Thank you.
Largo

GG

Hi Largo,

This is one of the shift (SN54LS673) register that I found. It has
16 outputs so u need only 4 of them (if my calculation right - but
never more than 5). Pick CMOS output if your fan out is only a single
LED (TTL output chips consumes more power but more fan out) . You can
design deferrent patterns only by using code without changing hardware
once assembled. Schematic is available in the data ***.

http://focus.ti.com/docs/prod/folders/print/sn54ls674.html
Data *** : http://www-s.ti.com/sc/ds/sn74ls595.pdf

GG's idea for using MAX7219 (decoder) is nice because u can save boards
space and current consumption. Those are multiplxed display drivers
(saves current lot) so it is very good to use them.

MaX7219 : http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1339
This IC can control the intensity as well.

4017 counters have 10 outputs. So u need 6 of them (provided u need one
active at a time) . But u need all off state thus only 9 output can be
used. Thats means you need 7 of them.


- Pubudu

.

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