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help on building a digital clock without PIC

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yingyingong

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only digital IC such as decoder and counter are needed. the time will be shown by calculating how many LEDs are lighted up for hours, minutes and seconds. so there will be a total of 85 LEDs light used.
-60 LEDs for displaying seconds
- 11 LEDs to display hours
- 14 LEDS to display minutes
plan to use 7490 counter and decade decoder to show 24 hours format time. any1 can help me on this?
 
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You're in luck. Building digital clocks is a popular type of project.

A search will turn up many websites where a builder supplies articles, schematics, photos, etc.

As you may know one of the tough parts is to adjust an oscillator until it is correct within 1 or 2 or 3 cycles per 100,000. Depending on how often you want to set your clock.

Or you may decide to simply detect the house current waveform and divide by 50 (or 60 if you're in the USA). It depends on which timekeeping source you regard as more convenient to work with.
 

thanks john. but got one problem. i'm not using 7 segment to showed the time. the time is known by counting the number of LED light up as shown in the figure.

https://obrazki.elektroda.pl/23_1319684991_thumb.jpg

for example: if the time now is 12.30, then 1 LED in column A, 2 LEDs in column B, 3 LEDs in column C and none LED in D light up.

so how should i connect the pin of the decoder?
 

I too was unclear as to what you're getting at. I thought you intended to place the led's around a circle. And light one at a time.

Your plan is not so easy to figure out. You want a bargraph of led's in each column.

One method is to use a 1-of-10 counter/selector IC (7441, 4017).
Or a 4028. One of 10 pins goes hi when a 4-bit binary value is entered.

The outputs go to a large array of 'OR' gates. You drive each led from one of these multi-input 'OR' gates. Example, your rightmost minutes column has 10 leds (or should it have 9?).

The led for '9' can be driven by the 9 pin of the 4017. That's all that it needs

The next one down is driven by a two-input 'OR' gate, whose inputs go to the 8 & 9 pins of the 4017.

Etc.

The bottommost led is driven by a 9-input 'OR' gate whose inputs go to the 9 lowermost pins of the 4017. (You'll need to combine a few OR gates to do some numbers.)

I guess the top pin of the 4017 isn't connected to anything. It's the zero. (I may be askew as to this line of thinking.)

The above is for just one column of your clock. You'll need to duplicate it 6 times. A few columns don't count all the way up to 9. They will be simpler to make.

You probably know how to make a 4017 count up to 5 and then start over at zero.

Here are IC's that may help you do this project.

4017 decade decoder (1-of-10 selector)

4028 / 7441 bcd-to-decimal decoder (1-of-10 selector)

===============

My Forrest Mims Engineer's Notebook has a page showing a bargraph made from one or more 74ls194 ic's. (4 bit shift register). Don't know if it will do what you want. Something like it is on Google Books:

The Forrest Mims circuit scrapbook - Forrest M. Mims - Google Books
 
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thank you BradtheRad but i still don't understand what you saying. do you mind draw the schematic out? thanks in advance.
 

I admit I was thinking off the top of my head. There's got to be an easier way. That's a lot of 'OR' gates. The schematic would look sort of silly.

In reality the first thing that came to my mind... is that the popular 3914 IC is really made for this job. All you have to do is apply the right volt levels. It will light up a column of 9 led's, first one, then two, etc. In bargraph mode.

I passed over the idea of a 3914 at first. Converting to analog spoils the exactness of binary operation. And it will be tedious to get nine output levels adjusted so precisely, to avoid making the wrong amount of leds light.

You would need five 3914's. (The leftmost led should turn off and on via an overflow pin.)

Each of your counter IC's would output a 4-bit binary number. It would go through a DAC. Then it would be analog through one wire to a 3914 IC. Its output pins will each be connected to an led.

Your DAC would either be an IC, or a resistor network. You would need 6 DAC.

However there's a way you might only need one 3914 and one DAC. By using the technique of strobing rapidly across the six columns. You would light up just one column at a time, very rapidly. The human eye would see all six columns lit simultaneously. Strobing also can use less power. It may or may not complicate your circuitry.

The idea of telling time by the number of lit leds in each column seems quite natural. An internet search should turn up somebody who's found an easy way to do it. Along with schematics, etc.

==========

I just realized. To light 60 led's will need ten 3914's, unless something ingenious can be devised. It may not be possible to split a range of a few volts into 60 divisions.
 

Why do you need 60 LED's for seconds?

There is something about this plan that isn't clear to me.

for hours, minutes and seconds. so there will be a total of 85 LEDs light used.
-60 LEDs for displaying seconds
- 11 LEDs to display hours
- 14 LEDS to display minutes
Click to expand...

The usual standard at the end of a minute, hour, or day in the 24-hour clock is to display the next value. Thus, the end of a minute is zero LED's lit, not 60, and so forth. Wikipedia describes some exceptions, but to light 60 LED's and not light the next minute could get confusing.

The other confusing thing is the use of columns for the individual decimal digits of hours and minutes, but not for seconds. Why wouldn't the display of 59 seconds require just 14 LED's and not 59?

John
 

The 60 led's for displaying seconds has been throwing me off too.

It does make better sense to use two columns for the seconds. The rightmost goes up to 9. The column next to it goes up to 5.
 

jpanhalt: my idea is to light up LEDs one by one for every second and the LEDs will turn off one by one after the first minute and light up one by one again for the next minute and so on.
 

anyone know how to connect the circuit to light up 20 LEDs using 7490 counter and 7442 decimal decoder and simulate using proteus?
 
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A picture is taking shape. Do you plan to use a circular face with 60 LED's spaced around the edge? To show seconds?

And then a few more for minutes? Etc.

What you plan to build will look terrific of course. And it may be simple to describe, and it may seem like it should be easy to build.

However it's a complex enough project that it needs to be assembled from a lot of simple building blocks. A full schematic doesn't just pop into one's mind. It will be a matter of assembling several digital IC's and finding out what signals to give them so each does what it does at the right time. Etc.

The IC's you mention may very well be the ones used by someone who built a similar clock. Or perhaps he used cousins of the ones you mention.

If you're lucky he made a website showing how he did it. Building electronic clocks is a popular project.
 

What you need are simple serial-in, parallel-out shift registers. You would need a type with some sort of (p)reset option, otherwise it would be impossible to turn all LEDs off at start of next minute.

Each second you clock a "1" into it, and the previous 1's move along 1 place. Then you use the 59th "1" as reset signal (preferably synchronous, so that next 1-second clock tick does the actual work of resetting all the bits). You can just connect last bit of a register to data input of the next register (until there's enough for the 59 second LEDs).

Result would be something known as ring counter or Johnson counter. Bit sequences would be like: (last one to become 1 would serve as synchronous reset)

(sec1)....(sec59)
000000........0000000
100000........0000000
110000........0000000
111000........0000000
111100........0000000
111110........0000000
111111........0000000
111111........1000000
111111........1100000
111111........1110000
111111........1111000
111111........1111100
111111........1111110
111111........1111111
000000........0000000

See the pattern? A simple shift register, no counter+decode nonsense.

BTW: I suggest you pay good attention to power supply in your clock (read: use enough decoupling capacitors, & in strategic places)... switching many LEDs @ once causes significant fluctuations in power consumption. If power supply isn't properly done, that might cause local GND/Vcc 'spikes' which could confuse logic IC's.
 

The shift register method looks suitable to operate 60 led's.

8-bit versions are 4021 or 74LS164. The clock will need 8 IC's just to show seconds.

However I see there are 16-bit and higher versions.
 

anyone know how to connect the circuit to light up 20 LEDs using 7490 counter and 7442 decimal decoder and simulate using proteus?
Click to expand...
One you understood how digital logic works, and how a single LED can be driven by a TTL output, you can answers these questions yourself. Proteus is a nice tool in this regard, but a TTL data book and pencil and paper should be sufficient. Just think logically.
 

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