Re: Large Scoreboard LED Displays
- From: Tim Mitchell <timng@xxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 7 Jun 2005 15:55:52 +0100
In article <tgbba1l67jk9tcnkod8ebh2mfuqssi6tq7@xxxxxxx>, Mark <Mark@?.?.invalid> writes
On Tue, 07 Jun 2005 06:47:08 GMT, Ross Herbert <rherber1@xxxxxxxxxxxxxx> wrote:
On Tue, 07 Jun 2005 06:25:41 GMT, Ross Herbert <rherber1@xxxxxxxxxxxxxx> wrote:
On Mon, 06 Jun 2005 23:36:16 +0200, Mark <Mark@> wrote:
Looking for idea's on the design of a large 3 -Digit, 7-Segment LED outdoor display scoreboard. The unit needs to be about 10 Metres away from the Microprocessor running things, I am uring towards discrete LED construction because of price, would like something like a two-wire interface (except power (I2C my preference)) any pointers would be appreciated. Mark in Spain mark@xxxxxxxxxxxxxxxxx (remove the X to reply)
I'm now thinking along the lines of Micro end feeds out I2C straight into MAX232. At the scoreboard display end, MAX232 feeds straight into 3x PCF8574 (one per digit with different addresses of course), will that work?
No it won't, I2C has a bidirectional data line, MAX232 has separate transmit/receive. I2C is designed to connect stuff inside a piece of equipment, not for those sort of distances anyway.
I would suggest using one 74HC595 per digit, which is an 8-bit serial to parallel chip. You just clock 8 bits into it and wiggle the latch line, the 8 serial bits then get latched to the 8 output pins.
You can use a ULN2803 (8 way darlington driver) as a power driver for the LEDs.
You need 3 control lines (Data, Clock and Latch) + power. I would advise having a Pic or something in the sign, and just send RS232 text to it to be displayed. The pic can then send the data to the latches. If you use the right pic it might even have enough I/O pins to drive the segments directly.
I have made a big LED sign this way (with the HC595) and it works well. -- Tim Mitchell .
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