Getting started need some info

T Chap

I am helping a friend build a controller board I owe a favor to. He is developing some signs fo sale that use LED's that light up approximately 4 words(maybe 20 leds per) in whatever sequence he wants. There will be cases for some of his customers to put running lights going around the sign, sort of an led chase sequence.

I was looking at using the SX28AC/DP-G for the simple version of his signs that just flash words on and off in sequence, but if the need came up to have it run a lot of leds in a circle I'd have some thinking to do to accomdate that many individual led's. A matrix would work with the remaining pins, maybe 8 x 8 for a total of 64 leds. Maybe there I could add a daughtboard later that had a serial link to the SX, and would give me a lot more outs?

Ok seconds issue. I don't quite get the SX key. Is it a device to plug into a 4 pin header that I mount on my PCB? Also, do I need a resonator, if so what speed? I gather that there is an onboard eeprom or flash memory, so there is no need for external program storage. If that is true, all I need is the chip and the resonator? If I put a 4 pin header(.10) on the board for programming, thats all I need right?

Third. What about using mosfets to switch the low side of the led banks? Just a resistor off the SX pin to a mosfet, and the board is finished unless someone has a better plan for low speed switching, I am open to ideas.

Thanks for any help

Bean

Originator99 said...
Ok seconds issue. I don't quite get the SX key. Is it a device to plug into a 4 pin header that I mount on my PCB? Also, do I need a resonator, if so what speed? I gather that there is an onboard eeprom or flash memory, so there is no need for external program storage. If that is true, all I need is the chip and the resonator? If I put a 4 pin header(.10) on the board for programming, thats all I need right?

You can either program the chip in the SX-Tech board and then move it to your PCB, or put the 4-pin header on your PCB, then you can program it in the board.

The SX can run from it's internal clock at 4MHz, 1MHz, 128KHz, or 32KHz. The speed depends on your applications. However, the internal clock is not very accurate (± 8%). So if you want to do serial communication you will need to use an external resonator. If you're just flashing LEDs, the internal is fine. The faster the clock the more current the SX will consume.

The SX28 has 2K of flash memory on-board to store your program.

You will need a 10K resistor from the /MCLR pin to the Vdd pin. And I would recommend a 0.01uF capacitor between the Vss and Vdd. Everything else is optional.

Sounds like an interesting project, keep us informed of your progress and feel free to ask more questions.

Mosfet would surely work. If you have multiple·LED banks you may want to use something like the ULN2803 chip.

Bean.

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Cheap 4-digit LED display with driver IC·www.hc4led.com

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"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh


Post Edited (Bean (Hitt Consulting)) : 8/22/2006 12:03:28 PM GMT

T Chap

Thanks Bean for the detailed response. I like it that the chip is self contained for certian apps. I am a little unclear about the comment "So if you want to do serial communication".... does this include programming by the SX key sas well? I'd be fine with the 4mhz internal without any extrernal resonators as long as I can still pulg in the SX key for indivual download. The ULN is a good tip, easier to deal with and smaller that mosfets.

Thanks

Bean

You can always program the SX with the SX-Key. That doesn't use the clock on the SX chip (there is a clock on the SX-Key).

If you do put a SX-Key header on your board, I would put a 0.01uF cap as close as possible to the header pins between the Vss & Vdd pins. The SX-Key draws alot of current when it fires up and if the voltage drops you will get error messages. The cap is just insurance, but I always put it on my boards.

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Cheap 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com

"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
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T Chap

I think I'll put traces and pads for the external resonator in case of future serial use.