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Topic: led screen (Read 2760 times) previous topic - next topic


Hi again , i thought at something more realizable for me: a board full of leds to show different messages (time,date,etc.) and to show sensors values.
I think it will be something like a screen. If you can help me with some ideas to start with like length,from were to start .The number of leds and the resistances are not a problem(my father can supply hundreds :) ) .Also if you can point some good tutorials, I've found some , but you never know.
Thanks for your support again.
Is thing matrix screen?


Jun 05, 2011, 08:18 pm Last Edit: Jun 05, 2011, 08:27 pm by Korman Reason: 1

[...] I've found some , but you never know.

You know, this is quite disrespectful towards all the people who spend their time to help others. If you found some tutorials you like, go ahead and use them. If you have a specific problem you're stuck, go ahead and post about it - most likely people will help you. But say: "I found some stuff I don't tell you about, please post better stuff for me" drive you very quickly on top of th ignore list of many people.

So, lets forget about this posting and you go back to your workshop and make a project plan of what you want to build. Then you think about what's the easiest thing you need to learn about to achieve this goal, make a small sub-project to try it out and learn it. Once this sub-project works properly, you go back to your main project and take the next unknown thing left to learn and repeat with a new sub-project until none are left.

And only once a few sub-projects work properly and you're stuck somewhere on a sub-project, once no tutorial seems to help, you come back and ask a question. And don't forget to include in your post a circuit schematic of what you do, your source code that compiles but doesn't work as desired, a description what works and what don't and finally links to the relevant tutorial if necessary. Then you'll get good answers.

Have a nice day in your workshop and much fun on the journey you're just starting.



sorry,never thought this way but your right.i'll post again when i have something new or problems. one last thing i'll use this tutorial http://www.instructables.com/id/Make-a-24X6-LED-matrix/ .What do you thing about it?
Thanks,and sorry again


That tutorial sounds reasonable, although you can easily extend it to 24x10 by fully using the the output pins Q0-Q9 of the 4017. Also, make sure the current limiting resistors match the colour of your leds. White, red, green and blue LED have all different forward voltages. For more details and how to calculate the current limiting resistor look here: http://www.kpsec.freeuk.com/components/led.htm#data



thanks for info.
i have some questions if you have time, searched about them but not found a good explaniation:
What are doing 4017 decade counter and 74HC595 shift register ,and how they work,and why i need to use them.Haven't find a simple and good definitions.


Jun 05, 2011, 11:50 pm Last Edit: Jun 06, 2011, 12:03 am by Korman Reason: 1
Sub-project #1: Learn to use Google

4017 decade counter --> https://homepages.westminster.org.uk/electronics/4017.htm
74hc595 arduino --> http://www.arduino.cc/en/Tutorial/ShiftOut

Both links amongst the top 3 hits.



Sub-project #1: Learn to use Google

lol :)



Jun 06, 2011, 01:16 am Last Edit: Jun 06, 2011, 01:21 am by Simpson_Jr Reason: 1
The idea is nice, I built something almost similar when I still assembled petrol station price signs for a living. Boards not passing the test were thrown away and I didn't mind dumpster diving.

I made a 24x8-screen showing time and proverbs, for short messages it was okay. I wish I used a larger board, used a couple more 595s and extended it to 32 or 40 x 8 to be able to show more characters at the same time.

6 dots high seems to work looking at the video and by looking at the program the author added a font for lower-case characters as well. It's a pity he didn't show 'm in his video, I wonder how readable those are.

The 595 and 4017 are used since you don't have enough pins on your arduino. After all, you need a way to address those 144 leds. By using just 3 pins and one 595 you can control 8 output pins. The beauty of the chip is that you can place several behind each other requiring no extra lines of the arduino.

The first one has its data input pin connected to the arduino and... also has a separate output pin for the next chip. By using three chips, sending 24 bits of info the right way and signalling the chips to show the info, the according  3x8 pins will go high/low depending on the bits you've sent.

Although you can't see it, in reality no more as 24 leds are lit on the board at the same time.
The top row is shown first, then number 2-6 and all is done in such speed that we humans don't notice 5 of 6 rows aren't lit. We can't notice differences beyond ~25 frames a second, in the same way video is nothing more as a load of pictures shown fast enough after each other.

The 4017 + needed transistors are used to connect ground to each different row of leds. The chip has 10 output pins of which only one is high. Every time it's addressed it skips to the next pin and the transistor attached conducts all leds connected of that row to ground. Leds connected to other transistors won't get any power and are off. After row 6 is done row 1 is addressed again. Before each next row is adressed... 24 bits are sent to the 595s again.

This may seem like a lot of work for the arduino, but the arduino can perform about 16 million instructions per second which is more then enough to let us humans see all rows&columns simultaneously. When scrolling characters from right to left (or reverse), you'll even need to show individual frames of those 144 leds several times before continuing to the next, otherwise the text would be shown too fast to read.

I hope I've explained it well, keep a solder sucker and extra solder tip on the desk ;-)


Thanks for support.I have also found those sites i hadn't understood them 100%.Wanted i simple explanation like @Simpson_Jr gave me

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