A digital design question
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From: Andy on 15 Jan 2010 00:26 On Wed, 13 Jan 2010 07:08:27 -0500, Bitrex <bitrex(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? 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.
From: don on 15 Jan 2010 11:31 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. don
From: JosephKK on 16 Jan 2010 00:13 On Wed, 13 Jan 2010 12:25:16 +0000, Raveninghorde <raveninghorde(a)invalid> wrote: >On Wed, 13 Jan 2010 07:08:27 -0500, Bitrex ><bitrex(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? > >What are you doing with the outputs from the LS93? Presumably you are >decoding these with other gates to drive a display? > >If so I would decode a count of 0 as 1, 1 as 2 etc. Then when the LS93 >hits 12 decode that to reset the counter so it runs 0 to 11. But then you would want to insert an adder so that 12:34 could be properly displayed.
From: JosephKK on 16 Jan 2010 00:22 On Wed, 13 Jan 2010 08:11:54 -0800, "Bob Eld" <nsmontassoc(a)yahoo.com> wrote: > >"Bitrex" <bitrex(a)de.lete.earthlink.net> wrote in message >news:Qq6dnXrFS-I2KtDWnZ2dnUVZ_s2dnZ2d(a)earthlink.com... >> 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? > >I realize that you are trying to learn digital circuit design but this is >really a job for a microprocessor. A PIC or some other processor can do all >of the functions of xtal clock generation, timing, BCD to seven segment >conversion, latching as well as drive LEDs or LCD's for the display on a >single chip. It can all be done in a few lines of code and is trivial >compared to using 1970's TTL technology. You might as well try to do it with >6SN7 tubes if you want ancient methods. How about filing out your own brass >gears to make a clock? > >I believe your time would be better spent learning a programming language >and how to accomplish various tasks in a processor than fooling around with >TTL. This would give you a foundation for a whole range of neat projects for >the 21st century. Plus the versatility of processors allows a virtual >infinity of designs in one type of device. Other than learning how to work >with a few NAND gates and D-Flops, there isn't any future in complicated TTL >methods for projects like yours. > > Not quite that simple grasshopper. Someone has to understand the guts of those uPs and uCs; or the day will come when we cannot make them any more.
From: JosephKK on 16 Jan 2010 00:35
On Wed, 13 Jan 2010 21:38:40 -0800, "Bob Eld" <nsmontassoc(a)yahoo.com> wrote: > >"Sylvia Else" <sylvia(a)not.at.this.address> wrote in message >news:01970b1e$0$14953$c3e8da3(a)news.astraweb.com... >> Bob Eld wrote: >> > "Bitrex" <bitrex(a)de.lete.earthlink.net> wrote in message >> > news:Qq6dnXrFS-I2KtDWnZ2dnUVZ_s2dnZ2d(a)earthlink.com... >> >> 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? >> > >> > I realize that you are trying to learn digital circuit design but this >is >> > really a job for a microprocessor. A PIC or some other processor can do >all >> > of the functions of xtal clock generation, timing, BCD to seven segment >> > conversion, latching as well as drive LEDs or LCD's for the display on a >> > single chip. It can all be done in a few lines of code and is trivial >> > compared to using 1970's TTL technology. You might as well try to do it >with >> > 6SN7 tubes if you want ancient methods. How about filing out your own >brass >> > gears to make a clock? >> >> And thus we end up with systems that use a programmable microcontroller >> to perform a three-way OR function. >> >> Sylvia. > >Somehow I suspect that a 12Hr clock requires a couple of more gates than a >three-way OR function. Do ya think? Actually I might use a less than a >dollar, 8 pin processor for a three input OR gate. Even TTL would be a 14 >pin part would it not? > If what you need is a three input or gate try this http://www.fairchildsemi.com/pf/NC/NC7SZ332.html SC70-6 package, single gate. 'bout 50 cents. |