Pepper said:
Im not worried about the programming side of things, I've been programming in various languages for years. I just don't know what type of microprocessor to use and the circuit design etc.
**broken link removed**
You experience was not evident from your first post. Sorry
This is mostly rambling but you may find it helpful as a starting place for your thinking. You did not provide any guidance on budget. I am thinking the following could be built for $200 to $300 including connectors. I suggest using PICs here because they are what I know. If you want to use another processor others can help you with that. This design idea is modular/expandable. You could build a less expensive one using fewer processors to control larger chunks (mabye all) of the display.
As pointed out by cadstarsucks the first thing you need to figure out is the timing. I
THINK the following will work.
I would use an identical controller for each 8x8(16) matrix. You will need 24 processor pins to control each display plus 2 pins for serial IO. To get this you need to use a 40 pin processor which gives you several spares. (you could go with a 28 pin chip and use an external shift register, not worth it IMHO)
This pin count assumes that each LED is either on or off. The beauty of this is that you can build one controller for one display and test it. When you get it working you build up the other 19.
Light the LEDS by setting the 16 bits that control color (top) then activate the row by activating that rows bit(side). This cycles through the display in half the time.
You could do a proof of concept on a solderless breadboard. Hook the PIC directly to the display with current limiting resistors on the 8 side. The key here is that you should only turn on one LED at a time on the 16 side. The real thing would use transistors that handled more current so you could light all LEDs in a row.
Your sign is a 2x10 matrix of these displays. Think of it as two seperate displays. The top 10 only need to store the top half of the image. Similar for the bottom 10. This cuts storage by 50%. So instead of 320 bytes you only need to store 160. This would work. You could move to the 18F series to get more ROM (and 48MHZ) if you need to. The PICs have a self write ability. You could use 2 banks of flash to store 2 images if you wanted. I am not sure exactly how that is done.
The 40 pin PIC16F877A has 368 byte of ROM. These are 20Mhz processors and cost about $5 each. Put transistors on each output pin. You can get transistor arrays in sip form.
Use a master controller to manage each matrix controller. It will program the images, set the initial position within the image. You still have to figure how to keep the displays in sync. Maybe use a dedicated pin on the master as a step line that is sent to each controller and serviced by an interrupt.
You can buy an Ethernet to serial converter for about $25 that will make that part simple. I can provide the link if needed.
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