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From: Andy on 17 Jan 2010 17:46
On Fri, 15 Jan 2010 09:31:26 -0700, don <don> wrote:

>Andy wrote:
>> On Wed, 13 Jan 2010 07:08:27 -0500, Bitrex
>> <bitrex(a)de.lete.earthlink.net> wrote:
>>
>> Here are the schematics of a clock I built in the '70s:
>> http://tinypic.com/r/1zb5f1i/6
>> http://tinypic.com/r/2lm78xv/6
>> The clock has been running for over 35 years.
>
>Please post some pics.

http://tinypic.com/r/de9r1l/6
http://tinypic.com/r/2rw52ix/6

>
>don
From: Bitrex on 18 Jan 2010 03:37
krw wrote:
> On Sat, 16 Jan 2010 03:05:11 -0800 (PST), wicore
> <williwie(a)hotmail.com> wrote:
>
>> On 13 Jan, 13:08, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>> I'm playing around with some 7400 series logic, trying to teach myself
>>> the basics of digital design. I've been able to come up with a working
>>> circuit for a 24 hour digital clock easily, but I'm struggling trying to
>>> think of a way to make a 12 hour clock. Specifically my problem is the
>>> reset of the hours counter - when the tens digit of the hours section is
>>> 0 I need the units counter to count from 1 to 9 and roll over to 0
>>> (for example 09 pm to 10 pm) but when the tens digit of the hours
>>> counter is a 1 I need the units counter to start counting at 1 (for
>>> example 12 pm - 1 am). I'm using 74LS93 series plain binary counters
>>> and assorted logic, and after working on it for a long while I can't
>>> think of a way to get it to work without using something like a
>>> presetable counter. Anyone have any ideas?
>> If I understand you correct you want the following sequnce:
>> 01 02 03 04 05 06 07 08 09 10 11 12 01 ...
>> I would recommend to use two synchronous counters with a parallel load
>> (eg 74x160/2).
>> Decode the state '12' to generate PE (parallel load enable) and set
>> the parallel
>> load value to '01' - done. Note that PE must also be a synchronous
>> input.
>
> Or decode '13' if the PE is asynchronous. It's really ugly
> (introduces a race and a lot of glitches), but it'll usually work for
> a clock.

Well, I've been playing around with this a bit trying to use the 74160.
The problem I'm having is that the reset is asynchronous but the load
is synchronous, so if I decode the "12" to generate a PE for the first
digit in the hours the counter never wraps around to "13" to trigger the
reset of the second digit. Is there a way around this or must I use the
74162? I don't think I have any of those here...
From: Bitrex on 18 Jan 2010 03:48
Bitrex wrote:
> krw wrote:
>> On Sat, 16 Jan 2010 03:05:11 -0800 (PST), wicore
>> <williwie(a)hotmail.com> wrote:
>>
>>> On 13 Jan, 13:08, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>>> I'm playing around with some 7400 series logic, trying to teach myself
>>>> the basics of digital design. I've been able to come up with a working
>>>> circuit for a 24 hour digital clock easily, but I'm struggling
>>>> trying to
>>>> think of a way to make a 12 hour clock. Specifically my problem is the
>>>> reset of the hours counter - when the tens digit of the hours
>>>> section is
>>>> 0 I need the units counter to count from 1 to 9 and roll over to 0
>>>> (for example 09 pm to 10 pm) but when the tens digit of the hours
>>>> counter is a 1 I need the units counter to start counting at 1 (for
>>>> example 12 pm - 1 am). I'm using 74LS93 series plain binary counters
>>>> and assorted logic, and after working on it for a long while I can't
>>>> think of a way to get it to work without using something like a
>>>> presetable counter. Anyone have any ideas?
>>> If I understand you correct you want the following sequnce:
>>> 01 02 03 04 05 06 07 08 09 10 11 12 01 ...
>>> I would recommend to use two synchronous counters with a parallel load
>>> (eg 74x160/2).
>>> Decode the state '12' to generate PE (parallel load enable) and set
>>> the parallel
>>> load value to '01' - done. Note that PE must also be a synchronous
>>> input.
>>
>> Or decode '13' if the PE is asynchronous. It's really ugly
>> (introduces a race and a lot of glitches), but it'll usually work for
>> a clock.
>
> Well, I've been playing around with this a bit trying to use the 74160.
> The problem I'm having is that the reset is asynchronous but the load
> is synchronous, so if I decode the "12" to generate a PE for the first
> digit in the hours the counter never wraps around to "13" to trigger the
> reset of the second digit. Is there a way around this or must I use the
> 74162? I don't think I have any of those here...

Nevermind, figured it out. I was trying to do some dumb thing like
loading on the first counter and resetting the second. I understand now
to load 1 on the first counter and zero on the second and use the PE on
both counters.
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