Driving Digital Clock

[ahmedragia21]

Hi, im trying to make a big digital clock , each segment is described as in the picture , the problem is i know how to drive 7-segment displays using BCD to 7-seg decoder , but in the display for example 00:00 has more than 7 segments as shown , what kind of decoder should i use ?

 

[ericgibbs]

Hi, im trying to make a big digital clock , each segment is described as in the picture , the problem is i know how to drive 7-segment displays using BCD to 7-seg decoder , but in the display for example 00:00 has more than 7 segments as shown , what kind of decoder should i use ?

hi,
Looking at the drawing, each digit has only 7 segments, the 'colon' dividing the hours and minutes is always ON.

Where are, the more than 7 segments.?

BTW, how are you going to display 21:00 hours.?

 

[ahmedragia21]

thanks for the reply ,
i mean of each digit it has 20 LEDs , how i will drive these all ? and i really didnt imagine they are 7 segment , how ? suppose number 8 is there , sure there are more than 7 LEDs will be driven ..

 

[ericgibbs]

thanks for the reply ,
i mean of each digit it has 20 LEDs , how i will drive these all ? and i really didnt imagine they are 7 segment , how ? suppose number 8 is there , sure there are more than 7 LEDs will be driven ..

hi,
Look at this attached image, it will give you some idea's on how to solve the problem.

If you dont follow please ask.

 

[DMW]

each of those 20 LED's should be divided into 7 'lots' and put in series [hopefully] meaning they really act as one LED.

7 segment is called that as there are 7 different horizontal and vertical lines that can be switched on or off to represent the numbers 0-9, 8 just uses all of them

Sometimes you see these multiplexed, so every 7 segment will have the same input, but a different ground.

We cant tell without a datasheet tho

and as Eric noted, it will have to be 12-hour clock

 

[ahmedragia21]

thanks , but can be divided into any slots i want ? like grouping the 4 LEDs and say they are A ..etc ?

 

[ericgibbs]

thanks , but can be divided into any slots i want ? like grouping the 4 LEDs and say they are A ..etc ?

hi,
Assume you have 4 LED's for each segment, wire the 4 LED's in series, make 7 segments like this for each digit.

With 7 segments you can display numbers 0 thru 9.

Once you have made one digit, make 3 more digits the same way.

Do you follow.

 

[ahmedragia21]

well that's the division i tried , really thanks for your help

 

[ericgibbs]

well that's the division i tried , really thanks for your help

This is the more conventional way. see image.

This way you can use standard ic's to drive the LED's

 

[ahmedragia21]

Thanks for the reply , but why you made the division like this , i mean how did you know it will work for standard ics like 74LS47

 

[ericgibbs]

Thanks for the reply , but why you made the division like this , i mean how did you know it will work for standard ics like 74LS47

hi,
The common numeric LED's are arranged in this way, 7 segments.
Look at the front of a standard number LED and you see this pattern.

The 7447 is designed to drive 7seg LED's with segs with this pattern.

The 7447 is an active LOW, open collector, upto 15V LED driver.

 

[ahmedragia21]

thanks so much