Large Scoreboard LED Displays

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 snipped-for-privacy@markXscotford.com (remove the X to reply)

I would suggest using an RS485 datalink instead of I2C to improve noise immunity over the 30 meters

Dan

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Dan Hollands

1120 S Creek Dr Webster NY 14580 585-872-2606 snipped-for-privacy@USSailing.net

If I understand what you are asking, you will need ten lines for this to do it directly with no electonics at the display, 11 with a decimal point. The lines are: 7 anode drivers (segments) and three cathode drivers. The drivers need to supply the required LED current which may be 100mA or more depending on type and brightness, plus if you series LED's to make large segments (rows of LED's), you'll need more voltage depending on the the number of LED's. Since you are only going 10 Meters and since it's a visual display, the speed of operaton is not important so you don't have to worry about terminating the lines or any other high frequency effects. I don't think I2C is necessary or even appropriate since you would need electronics at the receiving end. If you want to do it with a single serial wire pair you'll need electronics at the receiving end plus power. RS232 without any handshaking directly to and from the micros built in UARTs would be the easiest. But, I wouldn't do that for 10 Meters, I'd just run a 10 conductor cable, 20 AWG or something. You will need driver transistors to get the required LED current and voltage. All of the electronics and power would be at the control point with nothing but the LED's at the board. Keep it simple. Bob

Is this the sort of thing you are looking for?

PS.

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Update, I was looking to make the 3 digits all run from 4 wires (2 for supply 2 for control signals) to keep the interconnecting wiring down to a price. The unit does not have to run a lightning speed, it will only be updated every 250ms or so. The size I am looking to achieve is about 300mm high, so each segement would have about 16 LED's (dual row). I write all my code with PicBasic Pro, so the easiest communication protocol with this software is preferable. The supply voltage to the unit can be either 5V or 12V, both are available.

In article , Mark writes

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.

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Tim Mitchell

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?