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IC / Circuit type help for project

Does anyone have any idea if there is an IC out there that can do what I'm trying to do, or a way to do it relatively easily? Right now, I have a project where it interfaces with the parallel port, and controls 8 channels of relays. When the channel on the parallel port is 'on', it turns on the relay. What I want to do is similar, but on a bigger scale, and with the serial port. What I want to do is have the serial port feed into an IC or circuit, that ideally has a few source power pins, and a large number of output pins that it connects in parallel to the source. What I am ultimately trying to do, is have it control a 12x12 grid of RGB LEDs. Any thoughts that anyone might have would be extremely appreciated. I am more of a coder that dabbles with electronics, and this is a little over my head. I have a lot of experience soldering and doing more basic circuits, but I'm sort of at a loss as to what to even search for, or if there is a better way to do it. I will probably need at least ~450 channels. Thanks, Dan

Reply to
patcheswfb
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Reply to
Brendan Gillatt

Oh my god that cuts it down to less than 50 channels! wow, I would not have thought of that, thanks a lot! I have been talking to some other people, and thinking that a programible chip with say 50 logic gates would work. Thanks a lot for that!. there aren't any ics that have the capability buit in, are there?

Reply to
patcheswfb

I think what you're looking for is called a shift register. Shift registers take serial data in and then essentially fan it out across many pins.

Reply to
T

OK, so i've discussed it some more, and I don't know how well a programmable chip will work. What I really need is something like a mux - demux, where the program acts as a mux, and the chip acts as the demux, converting the serial signal to a parallel output. Any thoughts on how to do that?

Reply to
patcheswfb

Awesome, that does seem to do exactly what I want. I can't seem to find any that have more than 8 channels, though (8-bit), is there a reason or am I just not looking hard enough?

Dan

T wrote:

Reply to
patcheswfb

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formatting link

If you daisy-chain 9 of these and send the data pattern as a single serial string then you can light up whatever LEDs you want to and hold that pattern statically until you want to change it.

Then you just send another 144 bit serial bit stream down the line, latch it after the last bit gets clocked in and Voila!, there's the new pattern.

Power supply requirements aren't bad either. If you use 20mA LEDs and you turn them all on at once they'll need 2.88 amps from a 5 volt supply. OTOH, if you use 2mA high-efficiency LEDs that'll bring the current down to 288mA plus what the chips need to operate.

Big plus is you don't have to use current-limiting resistors.

BTW, please bottom post.

Thanks,

-- JF

Reply to
John Fields

Alright, i've been looking into multiplexing more, and I definitly want to try to do it, but I have a question. The concept is to have rows wired to a common controlled ground and columns to a controlled source. this way, to turn on a specific led, the row's ground is connected, and the column's source is connected. since that specific led is the only one that has both leads connected, that is the only one that turns on. Say, however, that you want to have 2 lights on, one in say A1, and one in B2. You connect A to ground and 1 to source to turn on the first light, and B to ground and 2 to source to turn on the second light. When you do this, however, wouldn't A2 and B1 also turn on, because those both have both leads connected? there has to be a remedy for this, every lcd in production uses matrixing. thoughts?

Dan

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patcheswfb via ElectronicsKB.c

Multiplexing involves rapid switching, so each LED is only on for a short period.

Typically, you might apply +V to the column A common lead, and ground to the common row 1, 3, and 5 leads, to turn on LEDs A1, A3, and A5, and hold that state for a few milliseconds. Then apply power to column B, and simultaneously ground rows 2, 4, and 6, for a few millisecs, lighting LEDs B2, B4, and B6. Continue for as many columns as you have, then repeat continuously.

Since each LED can only be on for a faction of the time (if you have

10 columns, 1/10) you can drive the LEDs with somewhat more than their rated continuous current if necessary to get the desired brightness.

The switching frequency should be fast enough that there is no visible flicker.

--
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
Reply to
Peter Bennett

Awesome, I think this will work perfectly. One thing though, is there any way to use this with multiplexing, as discussed above? I am doing a 12x12 RGB grid, which would mean 432 chanels if I do all of them individually, so I was going to try to multiplex them, but it does not look like you can have the chip connect the channels to ground when they are on, or am I mistaken? If I can sort that bit out, it looks perfect! thanks a lot for all your help, I really appreciate it.

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Reply to
patcheswfb via ElectronicsKB.c

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