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Led dot matrix intensity variations when connected more than 7 max


Moderators: Ajay, Junied , abbas1707, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph

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Chaitra

Thu Dec 25 2008, 09:53PM

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Hi all,

I am using single MAX7219 driver IC to drive single 5X7 dot led matrix display.
Then i am cascading '10 ' MAX7219 , in which i am able to scroll the message on them,
But the problem is the intensity on the 1-6 Led modules is very low where as for 7-9 its normal intensity.
I ma not able to find why is the thing happening.
Please can anyone help on this as soon as possible.

Thank you
Chaitra

pdi33

Fri Dec 26 2008, 02:42AM

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Joined: Mon Jun 04 2007, 09:28AM

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we should preferably use current limiting resistors for driving the LEDs to solve such a problem. But in ur case, as u are driving it from a different driver IC, i think u should post the schematic for us to find out the problem.

note that the brightness of the LEDs will automatically increase if the no. of digits scanned are less. So u will have to set the 'intensity register' appropriately to compensate for the difference in brightness.

[ Edited Fri Dec 26 2008, 02:51AM ]

* inspired to develop,developing to inspire *

Chaitra

Fri Dec 26 2008, 02:48AM

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It is as per the cascading diagram given in the MAX7219 datasheet.I am sending the attachment of the datasheet.

max7219-max7221_4.pdf

pdi33

Fri Dec 26 2008, 02:52AM

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Joined: Mon Jun 04 2007, 09:28AM

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u mentioned 5X7 dot matrix LED, but the diagram in the datasheet is for 7 segment LEDs. Which one are u using ?

* inspired to develop,developing to inspire *

Chaitra

Fri Dec 26 2008, 02:56AM

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Joined: Thu Sep 25 2008, 05:34AM

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ya..the i studied the datasheet given for 7-se and related it to 5x7 matrix..i studied in different sites on this and able to do scrolling display on the 5x7 (10 modules)...but the problem is intensity

Arun Kumar V

Fri Dec 26 2008, 03:30AM

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i think the issue of intensity/brightness has been greatly explained in the Maxim's datasheet, in case, if you have missed it here's what it says : you can set current with ISET resistor and /or intensity control register.

look here:

i worked with the same Max7219 for 8 digit seven seg display, which i used for freq.meter to "free" the micro from the task of multiplexing, it worked well but i haven't tried it with 5X7 matrix.

Arun

Chaitra

Fri Jan 02 2009, 12:09AM

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Joined: Thu Sep 25 2008, 05:34AM

Posts: 6
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Hi,

Thank you for ur suggestions.
The mistake was logical mistake,that was nothing to do with the intensity registeror the external resistors and capacitor for intensity control.

Now i am trying to connect another 15 modules of MAX and 5x7 Led .

Thanks
Chaitra


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love u all please i need a pdf text on microncontroller using c language, thanks.
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shazy | 09 Jan : 04:31

sir Ajay,can u help me regarding this problem, plzzzz

i need the trraffic light controller code along with comments, so that i can proceed what does it do, after two days i will present my project. plz send me as soon as possible, i'll b very thankful 2 u. i m waiting 4 ur reply.

shazy | 09 Jan : 04:28

hi abhinav, r u a student ?

shazy | 09 Jan : 04:16

for Mr. binu, sir i need the trraffic light controller code along with comments, so that i can proceed what does it do, after two days i will present my project. plz send me as soon as possible, i'll b very thankful 2 u. i m waiting 4 ur reply.

Ajay | 09 Jan : 01:50

thats ok.. i replied to your post. do check it

AbhinavChaurey | 09 Jan : 01:49

i will remember it next time sorry for this time.

Ajay | 09 Jan : 01:41

well there is no limit, but its better to stick to single thread till your problem is different. Like now you have posted in a new thread whereas it could be done in the previous thread only.

AbhinavChaurey | 09 Jan : 01:39

Good night to u all see u tomoro:bye

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