Go Down

Topic: SINGLE 3 DIGIT 7 SEGMENT LED (Read 21490 times) previous topic - next topic

Paul__B

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.

nickgammon


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.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

nickgammon


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:

http://www.gammon.com.au/forum/?id=11516&reply=1#reply1
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

Paul__B


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 usable link with an anchor


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

cupstacker

#19
Nov 29, 2013, 11:19 pm Last Edit: Nov 29, 2013, 11:21 pm by cupstacker Reason: 1
your display is  lot different..  http://www.gammon.com.au/forum/?id=11516

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?

Paul__B


is there a specific diagram for 3 digit 11 pin?


Didn't you like the one I gave you?

nickgammon


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


Mine has 12 pins, and yours has 11. Mine has one more segment which would account for the extra pin. So yes, there's a comparison. And that's why you have datasheets, they tell you what is connected to what.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

nickgammon

I just want to point out, before you get too bogged down, you can buy these things from eBay for $10.







You get 8 digits, the MAX7219 chip, the board, two capacitors and a resistor. Just solder it all together and you can display 8 digits, driven by four wires (Power, Ground, Data in, Clock).

You can even chain those boards together to get 16 digits:


Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

cupstacker

#23
Nov 30, 2013, 12:15 am Last Edit: Nov 30, 2013, 12:18 am by cupstacker Reason: 1
that's pretty neat, but this project just involves only a 3 digit display.. nothing more fancy than that

all i know is i got this mess and don't know what to do with it  :(
http://cdn.img42.com/183cf65cd9739615c8fc41f75e7eaf22.jpeg

thank you

CrossRoads

MAX7219 expects to source current into 8 anodes and and sink current from 1 digit.
You have to add extra hardware to use common anode, see this application note:
http://www.maximintegrated.com/app-notes/index.mvp/id/1196
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

cupstacker

what kind of extra hardware?

thank you

CrossRoads

Read the datasheet - shows which type of transistors and how to connect them.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Paul__B


MAX7219 expects to source current into 8 anodes and and sink current from 1 digit.
You have to add extra hardware to use common anode, see this application note:
http://www.maximintegrated.com/app-notes/index.mvp/id/1196


The display he has is a common cathode.  It only matters anyway if you wish to use the character generator which is limited to digits 1 to 9 and the characters "-EHLP" - if you wish to define other characters, you cannot use the internal character generator anyway.

I have previously cited the MAX7219 data sheet which has the connection diagram on the first page, and the pin diagram for the display he has.  It is only a matter of connecting the corresponding pins from one to the other, adding a 33k resistor as per the datasheet (and some bypass capacitors), and using the code Nick provided.

nickgammon


It only matters anyway if you wish to use the character generator which is limited to digits 1 to 9 and the characters "-EHLP" - if you wish to define other characters, you cannot use the internal character generator anyway.


Whether or not you use the internal character generator does not affect the electrical characteristics of the chip. That internal generator just saves you having to code bit patterns into your code if you happen to only want digits and/or the other characters you mentioned.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

CrossRoads

Here's a MAX7219 with 3-digit common cathode display.
Change the display to match your pinouts.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Go Up