an extension of the spi?

[mombasa]

I'm trying to make a giant scoreboard display driven by a max7219. The pic that drives the max7219 with a spi is placed on a card that is about 10 meters away. How can I take these signals so far?. Thanks to those who want to help me.

[Charles Linquis]

I would probably run the signals (at both ends) to an RS-485 driver and receiver. Run in full-duplex mode. This increases the number of wires required, but should guarantee signal quality - even if there is an offset between the grounds of the two ends. Add the termination resistors also. The datasheet for the 485 chip that you use will explain that.

[mombasa]

Charles thanks for your interest, I had thought about using a MAX485 to transmit data, but I do not know how to do because the signals being transmitted are three. Can I use three MAX485? Thanks & Regards

[Charles Linquis]

Yes, you can use 3 chips. There are some dual devices out there as well. It would take two of those.

[mombasa]

Thanks Charles for your help

[falingtrea]

The CS signal may not need a differential driver since it is static during the SPI transfer. So you would need 2 differnetial transmitters and 1 receiver on the source end and two recievers and 1 transmitter on the destination side for bidirectional transfers. The CS can be just a regular buffer chip, like a 74HC125.

[Charles Linquis]

It is true that the CS signal is not high frequency, but if any signal is driven by a logic gate, then there can be at most, a 1V difference in the GND levels of the two devices.

Since your units are separated (and most likely powered by different power supplies that are plugged into different outlets), the possibility of offsets and common-mode noise is high. Most 485 devices allow at least 5V between the GNDs.

The differential nature of the signaling greatly reduces induced noise as well.