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I'm using an FTDI adapter to power 6 separate strands of p9813 pixels. These pixels are located at least 4 feet away from the FTDI adapter. Each strand requires the single FTDI CTS out to connect to its Clock line.

The problem is that for each strand that I add, the clock connection seems to need to get shorter and shorter, roughly in proportion with the number of strands I hook up. So with 6 strands, I can't use more than 1/6th of the length I was able to use for one strand.

This is problematic because I need to run the clock lines at least four feet to the FTDI. How can I split the clock line to six separate wires while maintaining the integrity of the signal?

I'm using 24 AWG wire.

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1 Answer

up vote 2 down vote accepted

You need a buffer. Something from the 74 series will do the job: wire all the inputs to the CTS, and take each output out on a different wire.

You haven't said what voltage this is (5V? 3.3V?) or what frequency the clock is, so it's hard to make a specific part reccomendation.

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I've ordered one of these: digikey.com/product-detail/en/CD74HCT365E/296-2149-5-ND/38516. Will be receiving it this weekend and updating this thread once I've confirmed that it works :) –  featherless Dec 6 '12 at 23:27
    
Also, the FTDI breakout board from sparkfun is 3.3V by default, but I can switch it to 5V; doing so would improve the distance the signal could travel, correct? –  featherless Dec 6 '12 at 23:28
    
If the 5V is suitable for what's on the other end, that will probably help yes. Your buffer is tristate - don't forget to wire its ~OE pins to ground or you'll get no output. Note that it also introduces a small delay - if your clock/data is very fast you may need to put the data through a buffer as well to match the delay. –  pjc50 Dec 7 '12 at 10:00
    
In fact I think you have to switch the whole thing to 5V as that's a 5V buffer, and the P9813 looks like it needs 5V too. –  pjc50 Dec 7 '12 at 10:02
    
Will do! Looks like it'll be a bit of a pain to switch the jumpers. Will report back later today. –  featherless Dec 7 '12 at 22:17
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