i have a single 3 digit 7 segment led display - 11 pin

i also have some 74hc595's and MAX7219's to connect the segment display to - (i don't know which is best but i think it will be 74hc595??0.. i do not need the DP

11 buttons will control this display as follows
buttons 1-10 will consist of double press to fill the display, example of this

button 1 - you press once to get the letter A and then say you press button 1 again the display will be A01

buttons 1-10 are A-J and 1-10.... (A/21, B/2,C/3.....J/10)

button 11 will start the display at 000 and be the SET button


button 11 sets display to 000 buttons 1-10 are useless until this happens
select a letter with buttons 1-10
select a number with buttons 1-10
button 11 clears display - button 11 is useless until the above 2 steps happen

with whatever was set with button 11 will turn on a certain set of leds.. for now though i have a bi-color led for testing so let's go with A01 the bi-color led turns on red and A02 the bi-color turns on green


keep in mind that there will be an on/off switch to turn on before any buttons can be used.. but i am not concerend about that right now, just keep that in mind for later

thank you

Is there a question here?

maybe i should have questioned it better. how do i connect the segment display to 74hc595's and looking for some coding help. basically was going from my previous topic to this one because i changed the concept of the project, see my topic "delete this topic please". i posted this one right after and asked the other one to be deleted.

thank you

How are you going to display 0 (zero) and D, unless you use lower case d.
Display 1 (one) and i, you will have to use a single vertical segment for i.
I gather you want to display any combination A01 to A10, B01 to B10, etc up to J01 to J10.
The 11th button does a clear, 000.
Do I have the concept right.
All the buttons means you keep the maximum number of presses for any number will be 10, to get A10 or B10 etc.

You could use two rotary encoded switches, one switch as you turn it , selects A to J.
The other switch selects 1 to 10.
This way is you get the letter or number wrong you just turn the rotary switch back or forward to the right one.
It simplfies the controls to two knobs and a reset button.

Tom... :slight_smile:

yes, they will be all lowercase.. i don't like the rotary switches idea.. they must be push buttons.. could always add a clear button if needed.

my main concern is wiring up to the chip

thank you

Just use the MAX7219 - makes it all so easy. If you try to use the 74hc595, you are up for driver transistors, resistors and ten port lines. The MAX7219 uses three lines, one resistor a couple of bypass capacitors and does all the multiplexing for you. Even if it is the wrong common cathode/ anode for your display (you did not specify) and you cannot use the built-in character generator in the MAX7219, it will be preferable. And you do not need a library for it.

Obviously you are going to matrix your 11 buttons.

No decimal points.

one resistor a couple of bypass capacitors

ok, but how do i connect it all to the max7219? i haven’t found a tutorial or anything on it…

thank you

Well there is always the data sheet.
Or google even

Basically, it's all in the datasheet.

I am kind of waiting for you to specify your display - common cathode or anode and pin numbering.

i wouldn't be able to tell you, i got it from someone who had gotten it awhile ago and does not remember.. all i do know it has 11 pins.

Or google even
Arduino Playground - Max7219

I love the way that code is listed there - with the line numbers!

I wouldn't be able to tell you, I got it from someone who had gotten it awhile ago and does not remember.. all I do know it has 10 pins.

That is going to slow things down, isn't it?

OK, we now know it is a common cathode display.

Ahh! I could have sworn that you said it had ten pins. Seems it has eleven. And I think we know the pin numbering.

That plus the datasheet, should get you wiring it up.

3bit Common Anode Digital Tube 0.36in. red LED - still don't see how to connect it to a max7219 OR a 74hc595..

i also have some 74hc595's and MAX7219's to connect the segment display to ...

Funnily enough I have a page about connecting LEDs to a MAX7219.

Half-way down that page I illustrate using a 4-digit LED, a 3-digit one will be similar.

I think you can make common anode ones work by reversing the way the 7219 operates. Get it to sink rather than source current. I’m not sure about that. I think CrossRoads is the expert on that sort of thing.

Or this page: Gammon Forum : Electronics : Microprocessors : Hacking a scrolling LED strip sign

That shows a scrolling LED display using the 595 chips. Those are set up to sink current.

Turns out the MAX7219 actually has the character generator to drive 7-segment common cathode displays - but only with digits “1” to “9”, “-” and the characters “E”, “H”, “L”, “P” in Table 5 (useful for spelling “HELP”). If you want other characters, you will have to code all characters yourself.

Wiring is given in the “Typical Application Circuit” on the first page, various other information including the current-setting resistor value according to how many active digits there are.

Nick, you need to put “<a name =” links into your pages so you can reference individual sub-topics.

ok, but how do i connect it all to the max7219? i haven't found a tutorial or anything on it..

I found one here. Well, quite a lot more than one.

Nick, you need to put “<a name =” links into your pages so you can reference individual sub-topics.

I did that a while back for each reply on my pages. If you RH-click on “Reply #1” for example (at the start of a reply) and “Copy Link Location” you get a useable link with an anchor:

Ah yes. sorry, I didn’t search your source properly for anchors.

your display is lot different.. Gammon Forum : Electronics : Microprocessors : Interfacing LED displays with the MAX7219 driver

you have 8 pins on one side and 4 on the other where as i have 5 on one side and 6 on the other.. to me there is no comparison

all the tutorials i find are specifically for 4 digit and 8 digit and the pins are different so therefore they must be wired differently and so is the coding i'm sure.

is there a specific diagram for 3 digit 11 pin?