Large LED display driven by an RTC. Appreciate help with what approach to take.

I am working on a project that is ultimately a clock. It's a design, concept type clock. A slightly different take than any I have run across in trying to determine how to go about accomplishing my goal. The clock display will be 72 sections, each one backlit by LEDs(presumably portions of LED strips). Of the 72 sections, 12 will represent the hours, 1-12. The remaining 60 sections will represent the minutes, 00-59. The only sections that will be illuminated at any given time will be the ones that correspond to the current time.

I'm fairly new to the Arduino environment but do have a few smaller projects under my belt, with that being said, I would appreciate any advice on what approach to take to tackle this.

At this point, I am open to any board and peripherals necessary.

Some options that I have been thinking about:

  • Using addressable RGB strips, basically making the entire circuit one strip, placing sections of LEDs with the respective numbers and then only illuminating the LEDs that correspond to the time. In this scenario, I would certainly need some help writing code to illuminate the correct sections at the correct times.

  • Possibly using LED strips and shift registers? This is not something I know a lot about, was just an idea.

I am open to any suggestions and would be grateful for your input.

Are you using the LED strips to simulate the segments of a 7 segment display?

If so, imply wire one side of each strip to the supply and turn on the segments as required, exactly the same as using small displays.

There would have to be plenty of projects that have used seven segment display for a clock.

Weedpharma

No, not like a 7 segment display. The shapes of each of the numbers will be cut in a facade of some sort and then backlit by the groups of LEDs. Ultimately, there would be 72 different LED sections. 12 for the hours and 60 for the minutes. Each, just for example, would have say ten LEDs be it in a strip or singles that would illuminate the cutout for each of the 72 "digits". Picture a piece of wood with the numbers 1-12 (for the hours), and 00-59(for the minutes) cut into it. Then these being lit from behind by clusters of LEDs.

If the time is 12:36, then a cutout shape of "12" will be backlit and a cutout shape of "36" will be lit too.

Thanks for asking though, I thought this may take some explaining to get the idea to be clear enough. Maybe wording it another way will help clarify.

Can you supply an example of the layout of the numbers?

I cannot see why you need so many sections. I would think many would always be on at the same time.
IE, two sections but switched as one.

Weedpharma

No, not like a 7 segment display. The shapes of each of the numbers will be cut in a facade of some sort and then backlit by the groups of LEDs. Ultimately, there would be 72 different LED sections. 12 for the hours and 60 for the minutes. Each, just for example, would have say ten LEDs be it in a strip or singles that would illuminate the cutout for each of the 72 "digits". Picture a piece of wood with the numbers 1-12 (for the hours), and 00-59(for the minutes) cut into it. Then these being lit from behind by clusters of LEDs.

If the time is 12:36, then a cutout shape of "12" will be backlit and a cutout shape of "36" will be lit too.

Thanks for asking though, I thought this may take some explaining to get the idea to be clear enough. Maybe wording it another way will help clarify.

It seems you have the idea on your mind but, believe me, it's a bit confusing the way you explain it (60 strips for minutes suggests a conventional watcth -you know, placed in a radial fashion). :cold_sweat:

Regards

Ok, I'll try to give you a better idea. They are just numbers randomly arranged on a board. They will be cut out of the substrate allowing the LEDs to illuminate their shapes from behind. At any given time, only one hour "number" and one minute "number" will be illuminated to correspond with the time. Something along these lines. Here, it shows the time to be 12:36.

Hours Minutes

11 3 2 / 56 1 00 31 49 15 51 5 32 14 20

6 12 1 / 2 24 3 13 29 46 59 22 4 8 44

5 8 4 / 36 43 27 30 50 52 25 11 34 7

10 9 7 / 10 38 21 53 47 17 41 19 26 57

28 58 23 9 18 6 35 37 16 40

42 45 12 54 48 55 33 39

So what I need to do is get the time, say from an RTC, and then be able to light up the LEDs that go with the corresponding numbers on the board. The LEDs will not physically take the shape of the numbers in any way, they will strictly light them from behind. Picture small clusters of them for each represented number. That is why there are 60 sections for "minutes", and 12 for "hours".

Thanks for your patience while trying to help. I'm sure the concept seems a bit odd, and it does to me too, but it was brought to me by a designer that was looking for help in making the concept work for a particular design element in a project.

So you have the numbers "0".........."11" for hours with a light behind each and "0"........."59" for minutes.

For time you need one of the 12 hours lit and one of the 60 minutes lit.

You therefore need to convert the hrs to one of 12 outputs and min to one of 60 outputs.

You now need to know how to use the Arduino outputs to be converted to 1 of 12 and 1 of 60.

Weedpharma

You are correct sir! That sounds right. I guess that is where the real question lies.

I figured I would use an RTC to provide the time, then would need to code the arduino to switch on the proper LED sections. I'd like suggestions on which way to go in regards to the LEDs, should I use basically one long addressable led strip to reduce wiring,etc? This may put the programming a bit out of my limited arduino knowledge base. It seems that using regular LEDs, I'd have to use shift registers and and who knows what else to allow for that many actual outputs. Being there are only two small sections ever lit at any time, the hour and the minute, the power requirements should not be an issue and I could run the one adressable strip from an arduino with the proper coding.

Sorry for any confusion, I'm trying to be as concise as I can.

It's a typical example of the use of shift registers. It doesn't matter how many LEDs you have, they are just strung together and shift registers do the rest.

Have a look through this to get you pointed in the right direction.

Thanks KenF. Thoughts on what way would be better to approach it? With Shift registers or addressable LEDs?
The coding will most likely be my biggest hurdle no matter which way I go.

Thanks

I'd go with shift registers. In fact, if you have your minutes on one string, then to move onto the next minute, you'll just have to issue a single shift.

You could then put your hours into a separate string and the same would apply there. Simple stuff.

If you were to combine the whole lot as one long string you could save yourself the cost of one shift register, but the coding would be slightly harder.

Hmm. Time to study up on shift registers. Just from the quick look with limited info that you have, how many shift registers would be necessary? One for the hour side and one for the minute side? I was thinking I"d need a lot for the minute side because it has 60 separate sections.

I'll go look for some examples and see what I can come up with. Thank you for your input.

You can get 8 bit or 16 bit versions. so four of the 16bit would cope with 64 outputs. A single 16 bit or two 8 bit would cope with the 12 required for the hours.

You'll notice from this that both your hours and your minutes require 4 less than a multiple of registers. This is why you could save a register by combining the two.

72 outputs would require 9 registers (of the 8 bit kind)
60 outputs would require 8 registers
12 outputs would require 2 registers

8+2 = 10 (so one more than would be required than treating the whole lot as one string)

Great, thanks. I follow what you are saying. This will get me going for now. Time to go do some more searching/learning. I appreciate the help.

Just did a quick search to find out what the going rate is for these. Very first hit comes back as a pack of 10 of them :slight_smile:
Quite cheep really.

Nice! Thanks, thats great.

So I have a question in regards to what I had said about using them as one strip. I was referring to addressable LED strips in that application. Would those still require shift registers. I was thinking they would not.

I understand with regular LEDs or strips the need for them.

No, LED strips use completely different methods to address the individual LEDs.

Thats what I thought. So I guess it's back to that now. What approach would you take? Do it with addressable LED strips or normal LEDs and shift registers. The hardware costs are not really an issue at this time, but I am relatively new to Arduino and the coding practices so that would certainly factor in.