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Topic: Max7219 and Capacitors (Read 5476 times) previous topic - next topic

sensai

I was reading somewhere,, and it recommends,(mandatory) a 10 uf electrolytic and 0.1uf(100n)ceramic capacitor. I saw on a few schematic diagrams, these were on the +5 voltage pin... and I wonder... am if I am daisy chaining two or three of these, for more 8x8 led grids,,, do I require these capacitors, for each of the max 7219, or will one set suppress the noise signal for all of these. As I understand these should be connected as closely to the +5v and gnd pin of the max 7219...
Thanks in advance for all help and sound advice

PaulRB

I think one 0.1uF per chip is wise. As for the 10uF, I've not bothered before, but I suspect it depends on how long to wires are and the power supply. I would think if the wires are short, a 100uF for 10 chips would be just as good.

Paul

sensai


I think one 0.1uF per chip is wise. As for the 10uF, I've not bothered before, but I suspect it depends on how long to wires are and the power supply. I would think if the wires are short, a 100uF for 10 chips would be just as good.

Paul


You speak of length of wire,,, which brings my curiosity upwards. Is the noise a partial cause from impedance then? I was under the impression, that the noise, was caused from the reverse voltage "leak/drain" from diodes and such devices? If memory serves it was 0.7v or 0.3v, depending on the particular part. (it has been a while since electronic school). This then would feed back, and cause bits of power, going into the devices, feeding partial power to wherever it may "land". The capacitors, would take this, reverse voltage, and hold it, until it could release it in the proper direction of flow, therefore preventing this noise.
If memory serves well , we used to take a couple capacitors, and hook them inline with a power source, going to a car stereo, to remove the "whine" form the alternator. It was a really annoying sound. ;)

CrossRoads

That "somewhere" you speak of is the datasheet:
"Supply Bypassing and Wiring
To minimize power-supply ripple due to the peak digit driver currents, connect a 10?F electrolytic and a 0.1?F ceramic capacitor between V+ and GND as close to the device as possible. The MAX7219/MAX7221 should be placed in close proximity to the LED display, and connections should be kept as short as possible to minimize the effects of wiring inductance and electromagnetic interference. Also, both GND pins must be connected to ground."
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.

sensai


That "somewhere" you speak of is the datasheet:
"Supply Bypassing and Wiring
To minimize power-supply ripple due to the peak digit driver currents, connect a 10?F electrolytic and a 0.1?F ceramic capacitor between V+ and GND as close to the device as possible. The MAX7219/MAX7221 should be placed in close proximity to the LED display, and connections should be kept as short as possible to minimize the effects of wiring inductance and electromagnetic interference. Also, both GND pins must be connected to ground."

LOL ... Yeah the data sheet... well at least we know I was reading it... I read so much, I type into google what I am looking for and read it all,,,I generally keep most of it in my head,,, and there it is inductance, not impedance...That will stick in my head thanks. I also read ...somewhere... that it is best to ground these chips to the arduino itself... something about consistent current.

CrossRoads

All grounds need to be connected.  If the Arduino is the source of the 5V powering the MACX7219, then connect to the Arduino Gnd. If not, connect the Arduino Gnd and the Max7219 Gnd together at the power supply Gnd.
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.

Grumpy_Mike

Quote
something about consistent current.

No nothing about constant current.

What is with all the multiple ,,,,, it looks very odd.

sensai

#7
Dec 18, 2013, 04:14 am Last Edit: Dec 18, 2013, 04:23 am by sensai Reason: 1
Yeah sorry about the .... it is my mind in pause thinking while the fingers catch up ;) a nervous twitch?? LOL
And you are correct.. it said "That makes both circuits work on the same voltage-level." voltage not current.
Anyways I found my answer about the capacitors on this here schematic.
http://www.instructables.com/id/16x8-LED-dot-matrix-with-MAX7219-module/
This particular schematic shows both capacitors for each of the max7219 chips.

CrossRoads

Why did you not believe what I posted from the datasheet about the caps?
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.

sensai


Why did you not believe what I posted from the datasheet about the caps?

It has nothing to do with belief, my ability to learn something by looking at a picture is far greater then reading words... a picture just sticks better for me,,, and since I was looking for the thing about current, which was actually voltage,  I stumbled on that link, which gave me the picture.
I appreciate all the great knowledge you have supplied, and it keeps me looking for more. The words you used were singular, so I was unsure, if you were referring to each individually, or not. A picture clarified it for me in my head. I do not want to break anything, so I need to completely understand before I go ahead and hook anything up.
My apologies if I caused any grief. It is simply doubt in my own ability to understand.

CrossRoads

You wouldn't break anything by not having the caps, it just wouldn't perform quite as well; there is the potential for data transfers being corrupted internal to the chip. The caps help keep prevent that by keeping the internal power 'bus' steadier.
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.

sensai

So then , the only real possibility is just the information getting "trashed", opposed to the hardware, which then causes the "flicker" I have read about. This is good news because I spent $50.00 on two Max7219 chips. On the bright side, I have two more coming, of which I only spent 7$ for each max7219/led starter kit. LOL

CrossRoads

Yes, just bad data. $25/chip? Wow.
You gotta check out www.taydaelectronics.com, $1.25/chip, inexpensive shipping to the US at least.
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.

sensai

Thanks for the link,, things look much more reasonable there. Thanks for all the explanations. I now understand and am ready to build, fearlessly,,, even with 25$ chips.

JOEMro

Hi   I just received 10 max7219CNG DIPs    today.   

10PCS IC MAXIM DIP-24 MAX7219CNG
$4.80
Add: $5 for shipping.
from  "  http://www.idevopen.com/  " 
3 weeks for standard shipping.

do the search at the TOP of the page for more choices.

That's only $.98  ea.
I plan on firing them up tomorrow.
I'll let you know if the work.

I intend on using them for SIGNALING on my model railroad.
each chip can power 32 Red Green [Yellow] signals,   X 10 chips
$10 for a Nano, $.98 ea. for max chips that's only $.062 for each signal.
where other systems start at more than $3 / signal    not including wiring and the light.

Joe      :) :)

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