A digital design question
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From: Bitrex on 13 Jan 2010 21:58 Bob Eld wrote: > 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? What, you mean like this guy? http://www.jogis-roehrenbude.de/Leserbriefe/Bruegmann-Digital-Roehren-Clock/Digital-Roehrenuhr.htm > > 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. > I do have some experience writing code in C for microcontrollers like the AVR series. I'd like to eventually learn something like VHDL, but not having done much work with digital logic I thought this might be a fun challenge to get my feet wet. Right now the project is only a simulation in the "HADES" environment - it remains to be seen if I actually have the motivation to put it on a breadboard once it works in the simulator....:)
From: Sylvia Else on 13 Jan 2010 22:14 Spehro Pefhany wrote: > On Thu, 14 Jan 2010 13:19:06 +1100, the renowned Sylvia Else > <sylvia(a)not.at.this.address> wrote: > >> Bitrex wrote: >>> Sylvia Else wrote: >>>> Bitrex 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? >>>> Treat the sequence as >>>> >>>> 00 01 02 03 04 05 06 07 08 19 10 11 >>>> >>>> Increment left digit when right digit becomes 9. Clear both when both >>>> = becomes 12. >>>> >>>> Left digits are decoded as is. >>>> >>>> Right digits are decoded such that 0 is displayed as 1, 1 as 2,... 9 >>>> as 0. >>>> >>>> So the above sequence is displayed as >>>> >>>> 01 02 03 04 05 06 07 08 09 10 11 12 >>>> >>>> Sylvia >>>> >>>> >>> Thanks for your reply. I forgot to mention that I was hoping to use BCD >>> to 7 segment decoders for the output, and I think it's going to be hard >>> to shift the output of the counter like that so the appropriate digits >>> are applied to the input of the decoder. I guess I can decode the >>> shifted outputs individually but it'll take a lot of logic. >> Maybe use a 4 bit adder, catch the 1010 state and force the 1 ouputs to >> zero. Or catch the 1001 state going into the adder, and force the 0 >> inputs to 1, so that the address overflows to zero. >> >> I did a 7 segment decoder at uni. I don't remember it being so bad. It >> was part of an exercise of a technique whose name I no longer know, but >> I vaguely remember drawing squares around digits on a truth table. Maybe >> someone can give a name for the technique. >> >> Sylvia. > > Karnaugh maps? Yes. Thanks. Sylvia.
From: Sylvia Else on 13 Jan 2010 22:16 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.
From: Bob Eld on 14 Jan 2010 00:21 "Bitrex" <bitrex(a)de.lete.earthlink.net> wrote in message news:7rCdnSjYb56xFdPWnZ2dnUVZ_gWdnZ2d(a)earthlink.com... > Bob Eld wrote: > > > 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? > > What, you mean like this guy? > http://www.jogis-roehrenbude.de/Leserbriefe/Bruegmann-Digital-Roehren-Clock/ Digital-Roehrenuhr.htm > > > > > > > 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. > > > > I do have some experience writing code in C for microcontrollers like > the AVR series. I'd like to eventually learn something like VHDL, but > not having done much work with digital logic I thought this might be a > fun challenge to get my feet wet. Right now the project is only a > simulation in the "HADES" environment - it remains to be seen if I > actually have the motivation to put it on a breadboard once it works in > the simulator....:) Yeah, that's the ticket. A Vacuum tube Nixie counter. Now that's a project! I think making brass gears and mechanical escapements would be easier. So, you have programming and processor experience then what's with the TTL? I guess if you are just playing around and simulating for learning purposes then what the hell? If you are actually laying out a board, purchasing components, etc. Then I'm not so sure. In other words if it is a real project to get a complete working clock with minimum effort and cost, what then? Have fun.
From: Bob Eld on 14 Jan 2010 00:38
"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? |