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1  Using Arduino / Displays / Re: 4 digit display help on: May 10, 2013, 02:04:54 am

Using the 7221 is like outsourcing your laundry, leaving the Arduino for more serious activity.  Not only does it use 3 data lines but pin 13 may also be shared with other devices.

So is the 7221 a piece of hardware?
2  Using Arduino / Displays / Re: 4 digit display help on: May 09, 2013, 01:00:54 am
I'm sure the significance of that will be clear.

I'm guessing what you are saying is that i pretty much can't do anything else since most of my pins are used for the display? And i have the display working now. It's counting up and everything smiley-grin
3  Using Arduino / Displays / Re: 4 digit display help on: May 09, 2013, 12:16:46 am
Probably not lost for long, I suspect you are already encountering the next problem I was talking about and already have had to count the pins without any wires in them. Having the serial function cause the problem sounds like you have a clash on D0 &/or D1, and need to look for alternatives, or abandon serial comms.

So, you know what you've got, you know what you can't use, and you can now count what's available for other purposes, which isn't many. Now check the article again and note how many data pins are used.

I only have 2 pins left to use. I have used up 12 which was needed for the display which had 12 pins. So besides that idk what else im missing. That article says it only uses 3 pins to control the display.
4  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 11:38:21 pm
I meant the sockets on the Arduino. If that is what you mean too, then that is your next problem, hence my comment.

I can't comment on the segment not turning off, other than that with all those transistors and resistors around, you are unlikely to have done any damage.

Nope not what i meant. And found out my problem, it was the serial function causing it.

And im still lost on what i should get from that article.
5  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 11:03:03 pm
Well, that's a relief - and a good job well done.

Now might be a good time to count the pins without any wires in them, and then have a look at at that MAX7221 article.

But all the pins have wires. Though oddly enough a segment wont turn off now.
6  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 08:20:22 pm
I'm afraid this is what you do need to know about. The tutorial you allude to uses the microcontroller to do that. Your display is common cathode, like mine. The digits are selected by grounding their cathodes. In short, you don't mess with the pins, that's Arduino's job, as shown ion the bottom diagram. No ground wire needed, unless you want to make the arduino redundant.

Yay i got it working. I thought i had to ground it but i never thought of grounding it that way.
7  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 07:00:17 pm
I think you had better start by figuring out how the 'blinky' sketch works.  Then use that knowledge to get the same type of action with a single external LED.  Only then will you be ready to even consider dealing with a seven segment display, much less a 4-digit multiplexed version.


By 'blinky' sketch i assume you mean the blink sketch which i have already done and i already understand that. I already have my display lighting up and if it was a single digit display i would be fine and dandy. The problem i have is the 4 GND pins each control 1 digit each. Now how can i mess with the GND pins when they have to be connected to GND. I saw this tutorial which is very similar to mine here. Now if i understood that diagram correctly is it possible to have a jumper wire connected between the GND pin and the GND line?
8  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 05:18:18 pm
That would depend on how you connected it to GND in the first place.

If you are using a wire in a breadboard hole you pull the wire out.

If you are using a switch you open the switch.

If you are using a transistor then you bias the transistor (drive it with the proper base signal) until it is not conducting.

If you are using a microprocessor I/O port you make the port 'high' or '1'.


Well i would like something controllable by the code.
So the first way is out, along with the second.
The third way i don't really know anything about.
And the fourth way, how do i do that when those pins need to be grounded? As in how do i have a pin be grounded but also use an I/O port?
9  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 04:12:48 pm
You connect one of the cathodes (pin 6, 8, 9, or 12) to GND and the corresponding digit will turn on.


But how to i stop it from being connected to GND?
10  Using Arduino / Displays / Re: 4 digit display help on: May 08, 2013, 01:11:11 am
Okay so im using the 330 resistors, which i have connected between the pins of the display and jumpers connected to the arduino. Do i need resistors between the ground and the arduino? Now just some code?

Okay i have it lighting up somewhat, but it wont light up all the segments. And also how do i select each digit individually?
Scratch that got all the segments lighting up, except the decimal at the bottom. Though i still don't know how to select a certain digit.
11  Using Arduino / Displays / Re: 4 digit display help on: May 06, 2013, 11:29:43 pm
OK just make sure you are using limiting resistors. If they are not in the kit, it doesn't mean you don't need them.
Can do, but how do i know which resistors to use?

Probably correct. I'm an architect so I just use my workaday CAD and I don't know about the dedicated stuff, but it is around.  There is that Fritzing thing people use. I believe it is a freebie.
Okay ill try to get that working and see if i can produce a sketch
12  Using Arduino / Displays / Re: 4 digit display help on: May 06, 2013, 11:10:25 pm
You say you wired individual digits the same. This means you will have four digits displaying the same, rather than their own, data. However you also appear to have paid attention to the current requirements, thereby engaging on a pointless exercise, but not fatal.
Ohh i meant as in, i saw how a single digit segment display was wired. So i took that and expanded it on what i thought the 4 digit segment display should be like. If i'm correct or not, idk.

Don't ask, just read. If it's not particularly relevant now, it will be soon.
Okay will do.

At the moment you have a huge picture that takes time to load and is tedious to view. Those silly enough to wait eventually find it says nothing, which is likely to piss them off mightily.  When a wire disappears under a display, who knows where it's going? and those that don't know are not likely to care.  You might have a better time of it if you just move the display down one row.  A $2 kit of jumpers would give you some more colours. You won't regret that.
Ohh sorry about that. When i opened it it wasnt actually huge. I did wonder on the size though, it just never struck me. I think it would be better if i did a diagram. Any software to lay it out easily?

There may be minor differences in forward voltage with different colours, hence different current limiting resistors. I don't think this is particularly critical, just something you ought to be aware of.
Ahhh okay, i didnt know that thanks.

Where are your current limiting resistors?

It looks like you are trying to drive all four of your characters at the same time instead of multiplexing them.  Have you considered what the current draw would be (even if you did have the correct current limiting resistors installed) if you tried to display 8 8 8 8 ? 

Download a copy of the ATmega328 datasheet, find Table 28-1 and then look at notes 3 and 4 that follow the table.


I don't have any, unless it uses the onboard one, which im guessing the single digit does. I modified the single digit layout for 4 digits. Idk if i'm correct in that, it was just a thought. I didn't test it yet cause i wasn't sure if it would just blow up so that's why im asking here.

Multiplexing from my understanding somewhat comes from the code.

Though like i said in my first post, i'm new to this.
13  Using Arduino / Displays / Re: 4 digit display help on: May 06, 2013, 07:47:52 pm
i hooked my 4 digit display up the same except making adjustments for the increase in pin

Sounds like a wise move, but rather pointless. You might try checking here

As you appear to have nothing like it.  There are other methods, but this is about as simple as you can get.

A smaller and clearer picture that is more representative of what is happening will get a better response.

The data sheet you show may have a slight difference in the electrical characteristics.

Would you care to elaborate on the wise but pointless?

How would that guide help?

Smaller and clearer? Want me to rearrange the wires

I don't think the data sheet would have any differences just because they link the same data sheet for all 4 displays. I'm just not sure on my display because i got it in a kit. Here's a link to their page with the 4 digit displays.
14  Using Arduino / Displays / 4 digit display help on: May 06, 2013, 06:50:50 pm
I'm new to electronics, first time working with them. I already have done lighting up the led and have done a push-button switch.

I was wondering if i could get some help with the 4 digit 7 segment display. I saw how to hook up a single digit display, and i hooked my 4 digit display up the same except making adjustments for the increase in pins. I didn't hook it up yet cause idk if i could possibly damage my board or not.

Here is the spec sheet. Though it's for the green one i believe.

I attached a picture of my wire setup.
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