digital clock

[yukanti]

need help on non-microcontrolled component designing a digital clock.
just using simpe digital component.

[Bernius1]

Look through your junk drawer, & see what value crystals you have, & then look at "divide-by-N" counters. ( the 7490 is a divide-by-10, others are externally set to divide by a specific number). Or buy one at a garage sale, hack the crystal out, & wire your own divider circuit. If 'digital' refers to the circuit & not necessarily the display, then maybe a wall clock with concentric rings of LED's. It'll help you cheat out of converting binary to 7-segment, especially if your counter design is strictly cumulative, or has non-decimal output.
The goal is to take a crystal, say 4MHz or 100KHz, and count the cycles ( every 100,000 = 1-second ), and that advances your counter circuit by 1-second. Then every 60-sec. & 60-minutes. The logic problem is in the difference between base-2 binary, base-10 decimal, & base-60 clock timing.

[dacflyer]

see my thread replys "whats everyone working on"
i put several post there on the led clock i was making..217 leds.and i was using just 4017's
i even made the time base out of 4017's and the clock has been as acurate as any other clock i have in my house.
if you want more info contact me..

[philba]

If you want numeric output, look for BCD counters. 74xx162 is one. They aren't as plentiful as they used to be but you can still get them. use 2 each for the seconds, minutes and hours counters. You will need to watch the output and generate your own carry/clear when 6 is reached on 10s digits of the second and minute counters. 12 on the 2 hour digits (or 24 if 24 hr format). You can use 3 to 8 decoders for that. Its messy but reasonably straight forward. <p>Driving a 7 segment display is straight forward with LED display drivers.<p>Another approach is to use an 2Kx8 or larger rom (prom/eprom/eeprom/...) to generate the control signals for carry and clear. Think of the time digits as an address in a big array. Use the output byte for the carrys and clears to the counters. EPROMs show up pretty cheap on the surplus sites.

[yukanti]

oh yeah.. i've forgot to tell you that, i wana to design the clock with 7-segment....
maybe a schematic is available?

[philba]

What I outlined will get you there. I guess I dont understand - you want to design it or a completed design?

[rshayes]

Most clocks and watches to use a special 32,768 Hz resonator. This is easily divided down to 1 Hz by by 15 binary dividers.<p>The resonator is actually a small tuning fork made of quartz rather than a normal quartz crystal. You can probably find them in Digi-Key or Mouser for a dollar or less.<p>Starting at this low a frequency saves about 6 or 7 division stages and keeps the maximum frequency low. Both factors reduce battery drain, which allows a Lithium coin cell to operate the clock in a computer for several years.

[yukanti]

it's a school project, actually have search it on the web, but mostly using microcontroller. For now, i just want to dealing with digital, microcontroller not yet. A simple schematic is i actually need... along with explanation ofcourse, coz i kinda newbie here. In other way... "HOW TO" is more appropriate for my question.<p>thanks

[k7elp60]

Some suggestions for you. First decide if you want to display seconds. Then decide if you want to use 12 hour or 24 hour time. Then decide if you want it to be battery powered or work on line power.
If you want it to work on AC line power then you can use the line frequency as the time(clock) frequency. If you want it to be battery operated then you will need a oscillator to generate the time (clock) frequency. The choice of they type of clock with determine the accuracy. If you are using a oscillator to generate the time you may need a frequecy counter to adjust it on frequecy if you want extreme accuracy. If you are not concerned about accuracy then don't worry about adjustment as most circuits will be pretty close.<p>To display minutes you need two counters. Right hand digit that counts 0 thru 9. Left digit that counts 0 thru 5. Both of this digits can be done with ttl counters like the 74xx90. To display hours, right hand digit 0 thru 9, left hand digit either 0 thru 1 or 0 thru 2 depending on 12 or 24 hour time. If you want to display seconds then the counters will be the same as the minutes.
For decoder drivers I would suggest CD4543 as they will drive both common anode or common cathode LED displays.
Using my suggestions, the most difficult part is the circuitry to set the clock.

[yukanti]

Yup... second will be displayed too... i think 12 hour time would be enough.. it's only for school project... and battery as power supply ought to be enough.<p>what's next? i hope not as diificul as other schematic i've seen before

[Sterling Martin]

Sorry if this post is not appropriate! But I just couldn't resist! philba, what parts would a seven-segment digital clock like this take using a pic? Would the pic version of the same clock be as reliable?

[jollyrgr]

I want to build a NIXIE tube clock and figured I would use six 4017 chips (or similar) and a few logic gates to do the resets. The minutes and seconds are real easy to implement. <p>Many years ago I took a digital class that required each student to design a NAND and NOR gate from transistors. From there we could use NAND and NOR ICs. From the NAND and NOR ICs we could generate the other basic logic functions letting us use those chips. Such as decodes and basic "memory" devices. From there we built flip flops out of the basic gates and then coutners out of the basic flip flops. The final project was to build a digital clock. The hardest part of all of the design was creating a counter that would count 1, 2, 3,....9, 10, 11, 12, and then back to one; dividing it such that there were four separate "counters" as we had to multiplex the four digits and not use funky decoding for the hours count. In other words the two digits for the hours had to count as the hours do and output the signal in binary of the equivalent digits displayed; no special decoder.<p>Most of the designs I've seen for the NIXIE clocks use a lot of chips. I figure this could be designed using six 4017 (including a seconds counter) and a few logic gates to reset the counters. Ideas anyone?<p>Most of the

[yukanti]

so... anyone can help me on designing that digital clock? ASAP... if possible

[philba]

yukanti, shouldn't you design your own school project? Do you think some one should just give you the answer? You have gotten more than enough answers to put it all together.<p>[ February 03, 2005: Message edited by: philba ]</p>

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Sterling Martin:
Sorry if this post is not appropriate! But I just couldn't resist! philba, what parts would a seven-segment digital clock like this take using a pic? Would the pic version of the same clock be as reliable?<hr></blockquote><p>You can do it with 13 I/O lines and a driver transistor per 7-segment display to multiplex the 6 7-segment displays. A PIC can drive the individual segments directly but the common anode (or cathode) will potentially be 7 times the current so it needs a driver. 7 pins for the segments and a control line for each common cathode (or anode). You can use a demux to cut down on the control lines - a 74HC138 drops the control pins to 3.. The code will sweep through each display, lighting them in turn by outputing the segment pattern wanted and turning on the anode (or cathode) for that display. Persistance of vision makes it look like they are all on. Several ap notes on this technique at microchip.com<p>As reliable? why not? Probably slightly more reliable since there are fewer parts. Accurate - that's a function of the clock. If you use a 20 ppm crystal, you will get just as accurate time as anyone. The watch xtal (32768 hz) is a good idea as those are 20 ppm typically.