1Mhz -> 1hz What chip should I use?

[Eric]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

 

[Leon Heller]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

You could do the whole clock with a single CPLD and a 1 MHz oscillator.

Leon

 

[Tim Wescott]

We have to know your ground rules. "Least chips" these days would be to
build the whole clock using one FPGA, one CPLD or one microcontroller. As
your previous posts indicate you're doing this for a class and either can't,
or don't want to, take that approach (although CPLDs are pretty cheap these
days, and with Xilinx CPLDs at least the tools are free as well).

If you must start with 1MHz then you're pretty much limited to dividing by
powers of 10. If you must use discrete logic then using six 74LS90s or
three 74LS390s is probably best. If you can use 1.6384MHz then you can use
one 74HC4040 (which also has an oscillator section) to get down to 100Hz and
one 74LS390 to get to 1Hz.

 

[John Fields]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

A cheap micro would get you there with a single chip and, in the
bargain, do pretty much everything else.


You could also get there with six 'LS90's:


+--------------+
| +--------+ |
+--|>CKA QD|--+
| |
+--|>CKB QA|-------->1Hz
| +--------+
+----------------+
|
+--------------+ |
| +--------+ | |
+--|>CKA QD|--+ |
| | |
+--|>CKB QA|----+--->10Hz
| +--------+
+----------------+
|
+--------------+ |
| +--------+ | |
+--|>CKA QD|--+ |
| | |
+--|>CKB QA|----+--->100Hz
| +--------+
+----------------+
|
+--------------+ |
| +--------+ | |
+--|>CKA QD|--+ |
| | |
+--|>CKB QA|----+-->1000Hz
| +--------+
+----------------+
|
+--------------+ |
| +--------+ | |
+--|>CKA QD|--+ |
| | |
+--|>CKB QA|----+-->10kHz
| +--------+
+----------------+
|
+--------------+ |
| +--------+ | |
+--|>CKA QD|--+ |
| | |
1MHz>--|>CKB QA|----+-->100kHz
+--------+

Or you could use three '390's, or two '4059's, or...

 

[Bill Sloman]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

If you can't use a programmable logic device, the 74HCT40103 is an 8-bit
programmable divider, so you can set up three of them in series to divide by
100 each.

Farnell also seems to stock the 74HC40103 and HCF40103, if you don't
actually need TTL compatibility.

Farnell also stocks the LSI LS7060 32-bit binary up counter, and the LSI
LS7166 24-bit multi-mode counter. Some fifteen years ago we used the LSI
7166, and I think you might be able to use it as a divider. I've not been
able to locate a data-sheet, so I can't be sure.

 

[Ken Smith]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

Check out the CD4059 or 74HC4059

 

[Bill Sloman]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.

http://212.57.231.17/datasheets/107/KVONTUVPQS.pdf

gives a data sheet for the LS7166 24-bit multi-mode counter/divider, It is
designed to be driven by an eight-bit bus, so it needs some sort of
microcontroller to set it up. Weird part but Farnell has stocked it for some
15 years now, so somebody must be using it.

 

[Lewin A.R.W. Edwards]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need

Why are you using this relatively high-speed crystal, by the way? It's
easiest to divide by a power of two, and the less division you have to
do, the fewer chips. That's why the vast majority of clocks and watches
use 32.768kHz crystals and 15 flip-flops to divide it by 32768.

 

[mike]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need
to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.
Thanks in advance.

PIC16F877
That ought to give you enough pins to drive the kbd/display
directly and enough flexibility to add features.
mike

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http://www.geocities.com/SiliconValley/Monitor/4710/

 

[Wim Ton]

I'm building a digital clock, and I have a 1Mhz oscilating crystal. I need

to somehow get this to 1hz for the clock. If it matters, I'm using 74LS90
chips for most of the clock. What would be the way to do this with the least
amount of chips? If it's possible specific chip numbers would be nice.

2* 4040 12 stage CMOS divider and 1 * 4068 8 input NAND

Wim

 

[Roger Hamlett]

2* 4040 12 stage CMOS divider and 1 * 4068 8 input NAND

Wim

Though he says he has an 'oscillating crystal', if this means he just has
the crystal, another chip will be needed for the oscillator, or if one is
allready being used, a chip could be saved. The 4060, could be used instead
of the first 4040, which gives an oscillator as well.

Best Wishes

 

[Winfield Hill]

Bill Sloman wrote...

Ericwrote ...

http://212.57.231.17/datasheets/107/KVONTUVPQS.pdf

gives a data sheet for the LS7166 24-bit multi-mode counter/divider, It
is designed to be driven by an eight-bit bus, so it needs some sort of
microcontroller to set it up. Weird part but Farnell has stocked it for
some 15 years now, so somebody must be using it.

LSI Computer, Melville, NY. http://www.lsicsi.com
http://www.lsicsi.com/pdfs/LS7166.pdf

They still make all those cool cool chips. I used to order
a few hundred RED50/60 chips every year or so at Sea Data.
That was 20-to-25 years ago and they still make all of them.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Frank Bemelman]

Though he says he has an 'oscillating crystal', if this means he just has
the crystal, another chip will be needed for the oscillator, or if one is
allready being used, a chip could be saved. The 4060, could be used instead
of the first 4040, which gives an oscillator as well.

I would be tempted to ditch that 1MHz crystal and use a 32768KHz crystal
with a trimmer and a 4060. Also, if the OP meant a 1MHz crystal oscillator,
such as those square canned ones, he might discover that the accuracy
of the clock can be a bit dissapointing. 6 seconds per week is not unusual.