ICM7218, dot matrix display design discussion

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    I have some questions about a dot matrix display that I am trying
to develop. I am using an 8x8 dot matrix display. I have two ways to
display the required text, one is by using ICM7218AIJI chip, the other
is to write my own logic and design a circuit which does it. I have
done both of them with obvious trade offs:

1. By using 7218 I have a dedicated dot matrix refresh utility which
makes it more bright, reduces the area of PCB (PCB design area and
manufacturing cost are the most important factor in my design), reduces
load on the microcontroller, but it is not more suitable for scrolling
options than a dedicated logic.
    2. While designing dedicated hardware, I have actually used
decoders and ulns for grounding and a scanning function designed in the
microcontroller. The number of chips is huge and ofcourse results in
large area for PCB, not to mention since the scan time is very small
for each row or column, the applied voltage increases drastically.
Surprisngly however, the chips used are cheaper than a 7218 counterpart
for each dot matrix.

    My questions are as follows:
    1. Are there cheap 7218 resellers in China and Taiwan etc. which
can provide good quotations on bulk orders (say 100 pieces to start
    2. Does 7218 have an internal current limiter? I have given it
100mA, 150mA and 200mA, and each time it has resulted in increased
brightness, does it even have a current limiter, or is it designers job
to limit current on the chip?

Thanks in advance


Re: ICM7218, dot matrix display design discussion
On 11 Sep 2005 11:41:16 -0700, in comp.arch.embedded "Mak"

Quoted text here. Click to load it
P9 on the maxim data sheet
50R limits the current to 30mA per segment


Re: ICM7218, dot matrix display design discussion
Thnx Martin, most appreciate it

Re: ICM7218, dot matrix display design discussion
Out of general experience, is 30mA per segment sufficient for indoor
applications? How much is generally required for outdoor applications
where ambient temperature may soar upto 45 degrees Centigrade?

Is it better to stick to common Anode versions for more intensive light
solutions? Further if I am using a dot matrix which supports both
green/red LEDs, is it better to use two 7218s for separately lighting
the chips or using some form of active switch or relays for each
segment better?


Re: ICM7218, dot matrix display design discussion
7218's are about $3 in 100's, what price are you looking for? Why are
7218's not suitable for scrolling?

yes the discrete components to drive leds are cheap as dirt, but the
board area is not free either

Re: ICM7218, dot matrix display design discussion
dude where'd you get those prices from??? Farnell lists these chips for
6pounds or so...

I'll be pretty good with that price, can you direct me where I can buy
these chips from?

Thanks, and yes, the discrete components are a good solution but very
painful (increased area costs for the PCB and ofcourse
troubleshooting... ugh)

Re: ICM7218, dot matrix display design discussion
On 13 Sep 2005 01:40:01 -0700, the renowned "Mak"

Quoted text here. Click to load it

You can't fit two 18-pin SOICs and a couple of resistor networks into
less than the space of a 28-pin (DIP?) 7218?  And why do you say the
brightness is any different? The 7218 can manage a few mA per segment

BTW, it would be a cold day in hell before I specified that ancient,
huge and overpriced chip.

Best regards,
Spehro Pefhany
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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