Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.

share|improve this question
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.

share|improve this answer
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

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.