Hello AAC Forum,
Have been working on a large sequenced (320) LED display for some time now.
Worked first with MAX 7219 but got unpredictable results. Have redesigned
and rebuilt the display using 74HC595 shift registers.
https://forum.sparkfun.com/viewtopic.php?f=32&t=44668&p=191555&hilit=allenpitts#p191555
But as the blog explains when the display reached about 230 LEDS once
again the display became erratic. The Arduino just won't supply enough juice.
So now looking into two solutions.
The first is to use MOSFETS to use voltage instead of current to control the LED
voltage supply, like 2N7000.
Then I found Darlington arrays like UNL2803a which still use current but a lot less and instead
of having to wire eight discreet MOSFET devices to each 74HC595 (actually a SparkFun
breakout board called BOB-10690) use an octal array making construction much
easier.
So actually this is two questions.
1. Which solution, ignoring the construction hassle of the MOSFETs, would provide
the best chance of success? I thinlk it is the MOSFETs but would welcome some
expert advise.
2. Is there a MOSFET octal array? Like a UNL2803a but using mosfets instead of Darlingtons?
I have researched on 'MOSFET octal array' with no luck but perhaps the wrong terminology
is being used.
Thanks.
Allen Pitts, Dallas Texas
Have been working on a large sequenced (320) LED display for some time now.
Worked first with MAX 7219 but got unpredictable results. Have redesigned
and rebuilt the display using 74HC595 shift registers.
https://forum.sparkfun.com/viewtopic.php?f=32&t=44668&p=191555&hilit=allenpitts#p191555
But as the blog explains when the display reached about 230 LEDS once
again the display became erratic. The Arduino just won't supply enough juice.
So now looking into two solutions.
The first is to use MOSFETS to use voltage instead of current to control the LED
voltage supply, like 2N7000.
Then I found Darlington arrays like UNL2803a which still use current but a lot less and instead
of having to wire eight discreet MOSFET devices to each 74HC595 (actually a SparkFun
breakout board called BOB-10690) use an octal array making construction much
easier.
So actually this is two questions.
1. Which solution, ignoring the construction hassle of the MOSFETs, would provide
the best chance of success? I thinlk it is the MOSFETs but would welcome some
expert advise.
2. Is there a MOSFET octal array? Like a UNL2803a but using mosfets instead of Darlingtons?
I have researched on 'MOSFET octal array' with no luck but perhaps the wrong terminology
is being used.
Thanks.
Allen Pitts, Dallas Texas