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 alphanumeric led display with arduino?
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By: Leviathan34 (offline) on Sunday, November 15 2009 @ 06:24 PM PST (Read 19654 times)  
Leviathan34

Hey, I am experimenting with my arduino and I wanted to make a hexadecimal clock. So I was wondering if it is possible to use 3 of these displays with an arduino duemilanove. And if it is possible, then how to use the display with an arduino. (i.e. some example code) Any help would be greatly appreciated! Big Grin


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By: Windell (offline) on Monday, November 16 2009 @ 02:20 PM PST  
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Certainly possible, but not necessarily trivial. To drive one 17-segment alphanumeric display with decimal point, you need 17 lines of control. To control three, you can use 17+3=20 lines, where the third line is used to select which display you're addressing. Unfortunately, the Arduino does not have that many free display lines if you also need a serial or ICSP port available. If you don't, then you can pretty much hook it up straight, adding one resistor to each of those seventeen lines.

If you want more than three displays, you could use the three selection pins as inputs to a digital demultiplexer chip to select the display that you want, thereby driving up to eight displays from an Arduino.

This is probably actually a good demo project for us; we might consider doing a blog post about it.


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By: Leviathan34 (offline) on Monday, November 16 2009 @ 02:48 PM PST  
Leviathan34

Quote by: Windell

Certainly possible, but not necessarily trivial. To drive one 17-segment alphanumeric display with decimal point, you need 17 lines of control. To control three, you can use 17+3=20 lines, where the third line is used to select which display you're addressing. Unfortunately, the Arduino does not have that many free display lines if you also need a serial or ICSP port available. If you don't, then you can pretty much hook it up straight, adding one resistor to each of those seventeen lines.

If you want more than three displays, you could use the three selection pins as inputs to a digital demultiplexer chip to select the display that you want, thereby driving up to eight displays from an Arduino.

This is probably actually a good demo project for us; we might consider doing a blog post about it.



UMMMMMMMMM..... whats a demultiplexer chip and where can i get one????? How would I hook up the displays if I do have an ICSP or serial port available? Thanks for the help!


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By: Windell (offline) on Monday, November 16 2009 @ 03:04 PM PST  
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>whats a demultiplexer chip and where can i get one?????

It's a chip that takes several lines (say 3) and does binary decoding to set more lines (say 8) to the appropriate level. You can get one from major electronics shops. Again, we might do this as a project, which would require spelling out all the details.

>How would I hook up the displays if I do have an ICSP or serial port available?

Do you *really* need to have one while you're running this? Which one and why? That wasn't part of your original requirements....



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By: Leviathan34 (offline) on Monday, November 16 2009 @ 04:08 PM PST  
Leviathan34

Never mind about the serial ICSP thing... I was confused.


I looked up some demultiplexers on electronics goldmine. What kind should I use?


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By: Windell (offline) on Tuesday, November 17 2009 @ 01:36 AM PST  
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>I looked up some demultiplexers on electronics goldmine. What kind should I use?

As I said, if you only need three LED displays, then you won't need the demultiplexer. You may, however, need to use a transistor to switch the individual LED displays, depending on how much current that you want to drive them with at a given instant.

The microcontroller pins are each capable of 40 mA, but the total device current needs to be under 200 mA, so there are some tradeoffs necessary between how many LEDs are on at a time, maximum current per pin, and so forth.


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By: Leviathan34 (offline) on Tuesday, November 17 2009 @ 01:26 PM PST  
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Wait I thought you said that I couldn't hook up 3 displays because there aren't enough pins on the arduino.


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By: Windell (offline) on Tuesday, November 17 2009 @ 01:54 PM PST  
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>Wait I thought you said that I couldn't hook up 3 displays because there aren't enough pins on the arduino.

I'm not sure what's going on here. Either you're not reading carefully, or you are again changing your mind about what your requirements are.

I suggest that you back up a bit, decide what interfaces you need available for your project, and consult the Arduino documentation to figure out which pins and/or interfaces you have left to drive LEDs with. Once you get through that, perhaps you can rephrase your question and I can help you to figure out how to drive the LEDs.


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By: Leviathan34 (offline) on Tuesday, November 17 2009 @ 02:35 PM PST  
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I want to make a hexadecimal clock with 3, 17-segment LED displays using the Arduino Duemilanove. I can use any of the 13 I/O pins to do this. I do not need to have any of the ICSP pins available so I can use the ICSP pins if I need to. I need to know how to hook the displays up to the arduino and how to communicate with the displays using the arduino.

I hope this makes sense. This miscommunication is probably my fault. I probably didn't read very carefully and missed something. If you don't understand some part of this please tell me and I will do my best to explain. Sorry.


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By: Leviathan34 (offline) on Wednesday, November 18 2009 @ 02:52 PM PST  
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Quote by: Windell

>How would I hook up the displays if I do have an ICSP or serial port available?

Do you *really* need to have one while you're running this? Which one and why? That wasn't part of your original requirements....




I think the confusion probably came from here. What I meant to say and should have clarified earlier on was that I don't need to have an ICSP or serial available. So if I need to I can use all of them, but since I have a protoshield (from the arduino projects pack), I've never used the ICSP before. So if I need to use them then I will need to know how.


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By: Leviathan34 (offline) on Thursday, November 19 2009 @ 07:21 PM PST  
Leviathan34

So, any thoughts?


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By: karlgg (offline) on Thursday, November 19 2009 @ 10:14 PM PST  
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What I think was missed in the previous explanations was that you can use a single decoder to light a single display with only a few lines, and then use three more lines to choose which of the three displays was active. That way, you can go from one display to the next, displaying its digit for a moment before moving to the next. It's the same way most LED displays work, just flickering too fast for you to notice.


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By: Leviathan34 (offline) on Sunday, November 22 2009 @ 01:31 PM PST  
Leviathan34

Thanks for the help guys. I thought about some of the things you guys said and I think I know how I'm going to wire it now.


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By: Windell (offline) on Sunday, November 22 2009 @ 01:45 PM PST  
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> I think I know how I'm going to wire it now.

Great-- just watch the current limit on the Arduino pins.

We've also just got some chips to do this as a demo project-- should be able to do that soon. Big Grin


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By: Leviathan34 (offline) on Friday, November 27 2009 @ 04:38 PM PST  
Leviathan34

UGGGG!

Well I thought I knew how I was going to wire it... I was going to use 14 segment displays in digital pins 0-13 and use three analog pins to switch transistor using analogWrite()... Then I realized that the analogWrite() function uses the digial I/O pin Razz. Grrrrr. So know I'm pretty much back to square one.

I remember you saying something about the ICSP pins, but their was a lot of confusion and I got lost. Could you please repeat and clarify on that thing about the ICSP pins? I think it may be beneficial.


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