I am going to make Big Digital Clock Using PIC.
Big mean it's length will be 2 feet approx... and it will be wall mount.

Schematic




Plz see the picture carefully and
All type of suggestions are welcome.
Which function u like to be in this Clock...

I am in hurry now... and will discuss it later..

Thanks.

 

Hi Ayne,

(1) I wonder if your 4511 and your 7405 devices can source and sink the 'peak' current required to drive the displays to full brightness at a 1/6th duty cycle?

(2) What are the voltage/current ratings for the large 7-segment displays you plan to use? Some of the really large displays use series LEDs to make up the segments and you may need a higher source voltage.

May I offer an alternative driver method (below) for a full brightness display with PWM brightness control and fade-to-black capability? This method uses 8 I/O pins, common anode displays, a single MIC5821 8-bit serial-to-parallel 500-ma sinking driver IC, and 600 to 800 ma PNP source drivers.

Have fun and good luck with your project.

Mike

Attached Images

Matrix 7-Segment.PNG (48.4 KB, 52 views)

 

Just wondering why common anodes are used, could you not use common cathodes, or was it just because you had them on hand?

I'm mostly curious about the dimmer function, and scoping out its features/requirements.

__________________
Spency.

PIC Micro's - Your mind is the limit

PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

 

I am attaching two Picture...
Want to know that which is the best way way ???





For knowing 4028 and 7405 see my first POST(Pictures)..

Thanks

 

You may or may not have seen this really big clock!!!

http://www.sparkfun.com/commerce/pre...p?p=GPSClock-1

Looking forward to the end result.

Mark

 

That, That is soo cool

__________________
Spency.

PIC Micro's - Your mind is the limit

PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

 

Yeah...... That's enough...

 

Ayne,
If you are going to use the large (four inch high) seven segment displays such as Kingbright SA40-18EWA then you need about an 8 volt supply to light them as they use 4 leds in series for each segment.

If you want larger digits then you could have a look at the five inch 7SR50011AS (about twice the price of the 4 inch type though) and they need about 9v supply.

Or you could make your own displays or use ready-made modules.

 

I am going to make my own 7-Segment Display...
All LEDs will be parallel in it and i will use 5volt...

Below is the circuit.. I never parallel LM7805 before.
I want to increase current.. This technique will work!!!... I am using LM7805 because thisa is only available in our local market..
Resistor i use is 0.33 Ohm



Need improvement??
It will work??

Thanks in advance.

 

No, the regulators will not work properly in parallel because the will not share the load equally.
If you really want to stick with using 5v for the displays then an old pc at or atx switch-mode power unit may be a better solution because it would be far more efficient at high current and very cheap.

 

Now i am planing to copying the design of
http://www.sparkfun.com/commerce/pre...p?p=GPSClock-1



Is there any better solution, low coast??

T.

 

You can't drive the multiple led segments directly from the 4511 chips because their absolute maximum current per output is only 25mA.

The Sparkfun design uses an uln2003 driver which contains seven transistors each rated at 500mA and I think it also uses a 12V supply for the pairs of led light bars.

You will need to either use one of those chips or 7 discrete transistors to do the same thing.

 

In an earlier diagram, you show 2N3904 and 2N3906 as current switches. Although they can withstand 200 mA before blowing up, these transistors are not suitable for current over 100 mA. And with your base drive of (<0.5 mA), their saturation current is only about 5 mA.

 

Well, using transistor drivers would take care of 'peak' current concerns but you probably want to use heftier transistors like 2N4401 & 2N4403.

Using an NPN column driver in the 2nd circuit is probably not a good choice. A PNP would be better but then you'd need active low signals and your 4028 is active high. Perhaps a 74HC138 3-to-8 line decoder would be a suitable replacement for the 4028 and you'd have an extra pin left over.

The 1st circuit with the 74LS05 open-collector IC driving a PNP column driver transistor would allow you to use higher voltages if you decide to try those super size 7-segment displays which have several LEDs in series for each segment. I believe the new white and blue displays also require higher voltages.

You mentioned in a subsequent post that you were considering operating multiple LEDs in parallel for each segment. I'm not sure that's a good idea since it would increase the 'peak' current demands.

Those two transistor circuits show common anode displays but in a subsequent post you're showing common cathode displays. Have you decided which type display you're going to use?

Take care. Mike

 

The hardware dictates the choice of common anode displays. I simply haven't found any 8-bit serial-to-parallel sourcing drivers similar in function (and current capacity) to the MIC5821 sinking driver and I didn't want to use 2 chips.

The PWM brightness control uses a PWM period equal to the column 'scan' rate. Brightness is inversely proportional to the PWM duty cycle; 5% PWM = 95% brightness, 100% PWM = 0% brightness. If you enforce a minimum PWM duty cycle setting you can use the Port B column driver bus as a data bus to load the MIC5821 shift register at the beginning of the interrupt cycle when the display is off (before the PWM signal goes low -> display on). When using multiple MIC5821's in a large matrix display you simply throw 8 bytes in a row onto Port B with a Clock pulse after each byte at the beginning of the interrupt cycle to load all of the 5821's in parallel in about 4.8-usecs. ISR 'overhead' for driving a large 512 LED matrix (eight 8x8 matrix displays) is approximately 5% with a 20-MHz clock (50-usecs each 1.0-msec interrupt cycle) and the algorithm should port over to C or your favorite BASIC without difficulty. A minimum PWM setting of 1-2% provides plenty of time for loading the shift register(s) at the beginning of each interrupt cycle.