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Topic: Small 8x8 matrix driver? (Read 6402 times) previous topic - next topic

fungus


$1.36 in the quantities he is talking about if this makes it to production.  Atmel prices their product pretty darn reasonable if you ask me.


Yep. The ATmega is probably cheaper then the MAX7219.

I bought a dozen ATtiny84s from Farnell las week for 94 cents each (Eurocents). They want 10 Euros for a single MAX7219.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Nadav Ami

Yep you really cant compare the two in terms of price. If/when I do finish the project, ill be sure to post the code so everyone else can take advantage of the cheaper driver.

dhenry

The whole concept of buying max72xx now makes zero sense to me.

Those guys go out of the market for a (very good) reason.

Nadav Ami


The whole concept of buying max72xx now makes zero sense to me.

Those guys go out of the market for a (very good) reason.


Well there is an advantage to it, especially in very large quantities, and thats the fact that you don't have to program an extra MCU. But yes, cost (and possibly even feature wise) the atmega is the clear way to go.

CrossRoads

Not so clear - say your application called for DIPs instead of surface mount.
taydaelectronics.com has MAX7219 in DIP for $1.25.  I just bought 8, shipping was $1.80. Order also included 20 panel mount power jacks, 4 toggle switches, and a mess of resistors.

vs $2.78 (qty 25) for lowest priced 168 in DIP
http://www.mouser.com/ProductDetail/Atmel/ATmega168-20PU/?qs=sGAEpiMZZMtkfMPOFRTOl51o10QgrNfF
and $1.59 at digikey
http://www.digikey.com/product-detail/en/ATMEGA168A-PU/ATMEGA168A-PU-ND/2271215
both charge something like $6.95 for lowest priced shipping.
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.

Nadav Ami

Hmm...good point, though I don't know how reliable they would be in orders of 100. Then again, they might be great. It's too bad they didn't make one of the MAX72xx's in a smaller package...

CrossRoads

It is available on 24-pin wide SO surface mount package - its just a little thicker than you wanted.

Or as bare die if you wanted it really thin.
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.

Nadav Ami

#37
Oct 13, 2012, 07:26 pm Last Edit: Oct 13, 2012, 07:30 pm by Nadav Ami Reason: 1

It is available on 24-pin wide SO surface mount package - its just a little thicker than you wanted.

Or as bare die if you wanted it really thin.

A bare die would be great, though how would I go about soldering that (or having it soldered for me) in a cost effective and simple way?

Edit: I just did some googling, and it I think the bare die would be overkill for this little production run.

dhenry

Quote
It's too bad they didn't make one of the MAX72xx's in a smaller package...


I wonder why that's the case, ...

CrossRoads

Another advantage might be interface speed.
MAX7219/7221 can receive data at 10 MHz.  I use  mine at default SPI settings which I think is 4 MHz.
If your main processor was really tied up and you wanted to send stuff out at 8 MHz to get it out of the way quick. The master can do that, I think testing has has shown a 168/328 cannot receive that fast tho due to the slave having to sample (the CS pin?) or something along those lines.
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.

Nadav Ami


Another advantage might be interface speed.
MAX7219/7221 can receive data at 10 MHz.  I use  mine at default SPI settings which I think is 4 MHz.
If your main processor was really tied up and you wanted to send stuff out at 8 MHz to get it out of the way quick. The master can do that, I think testing has has shown a 168/328 cannot receive that fast tho due to the slave having to sample (the CS pin?) or something along those lines.

Yeah, ideally that would be the way to go. But size and cost are really the most limiting factor.

dhenry

Quote
a 168/328 cannot receive that fast tho due to the slave having to sample (the CS pin?)


True, when implemented poorly.

CrossRoads

Quote
True, when implemented poorly."


False - max speed is a hardware function, not something  users have any implementation control over:

"In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of
the clock signal, the minimum low and high periods should be:
Low periods: Longer than 2 CPU clock cycles.
High periods: Longer than 2 CPU clock cycles."
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.

Nadav Ami

Still though, shouldn't 115200 baud serial be fast enough for this application?

CrossRoads

Yes.  The above was only discussing reasons why the ATmega is not always the clear way to go.
In this case, your need for overall thinness, similar cost, and no need for ultimate in interface speed indicates the Atmega is the way to go, as long as your time to develop the max7219 function is not factored in.
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.

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