Adding 60 LEDs to digital clock to mimic second hand

Reprogramming the PIC is far simpler than whatever circuit would be needed if you don't.

Luhan

This comment does not give much thought. I suggest two 4017, modulo-60 counter driven off the tens-of seconds and seconds of the displays.

Can anyone site actual schematics? Any other suggestions? Largo

Hi,

4017 will not fit his requirement. This is a jhonson counter and at a time, only one LED will lit. For my knowledge I think programming the microcontroller will be far easier than making addiotnal circuits. Anyway microcontroller pins are limited thus it is better to use shift registers.

Pubudu

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'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? Do you want 1 LED lit at a time? 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? 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

GG

Yes.

Yes

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.

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

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 sheet.

Data sheet :

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 :

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

He could do it with 2 4017's, I think. First 4017 selects Units position leds 0-9 6 leds at a time; second 4017 selects tens position (which group of 10 leds) is "active"; each time the units 4017 goes 9->0, the tens 4017 gets advanced 1 by that transition.

Ed

ehsjr wrote: > Pubudu wrote: >

True but you have a units and a tens counter that would need to be gated to drive the separate LEDs. That 74LS673 could do it with 4 chips driving the LEDs directly though with only 8 mA but that should look OK, especially if high effeciency LEDs are used. The '673 has the async clear to be reset at each minute and then set data to '1' and clock in the first bit. Then clear the data and clock 59 more times and repeat for the next minute. Software-wise, if the 3 lines are available, it would be pretty simple.

BTW, the TV station I worked at had the Leitch clock mentioned.

GG

HI GG,

You are right.first I thought he needs more than one LED has to be on at a given time. But he needs one on at a time. Thus it is possible to ise 4017. Thanks for your opinion.

Pubudu

HI GG,

You are right.first I thought he needs more than one LED has to be on at a given time. But he needs one on at a time. Thus it is possible to ise 4017. Thanks for your opinion.

Pubudu

The point was that you don't need 6 4017's.

I'm not recommending one way over the other. Just pointing out that the 2 4017's suggested by Largo would work.

Ed

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Some other posts suggested 3 io lines driving the shift registers, presumably clock, data, and reset. But if you don't have enough io lines, those three lines need not be additional io's, as follows:

Reset - You don't need the reset line because you can just shift in 64 zeroes whenever you need to clear the SR's.

Clock - You have 2 spare outputs from the 3 to 8 decoder. Use one of them to clock the SR's. Eg, select output 7 so it goes low, then select some other output. (You could also use one of the spare decoder outputs as an SR reset line.) (Of course, if you do have an io available from the micro, just go ahead and use it for the Clock output.)

Data - Attach one of the segment io's to the SR data input as well as to its current segment. Sending segment data won't affect SR data because when you are sending segment data the SR clock isn't changing.

Hookup: The Clock output line connects in parallel to the 4 SR Clk lines. The Data output line connects to the first SN54LS673's Ser input. The data input lines of other SR's hook to the Y15 output of the previous SR in the chain. Each of 60 SR Y-output lines is attached to an LED through a resistor.

In normal operation: At second #0, set the data line to 0 and blip [lower and raise] the clock 64 times to clear the SR chain. At second #1: Set the data line to 1 and blip the clock. At other seconds: Set the data line to 0 and blip the clock.

You could make different patterns on the LED's for conditions such as alarms.

-jiw

take a look at

Steve Roberts

Nuts and Volts published a 2-part article (Aug & Sep 2003) written by John Carter on a clock ("Ben") that used individual LEDs (no 7-seg displays). The minute "hand" works like you want your second "hand" to work. HTH

-Dave Pollum