1
\$\begingroup\$

I have a 2 meters WS2812 ledstrip connected to my raspberry and it works fine. Does anyone knows what the maximum length can be between the raspberry and the start of the led strip? I tried a 5 meters long old CAT5 cable I had laying around but this caused already the leds to be less bright and had problems with the refreshrate. Anyone has any experience with this?

\$\endgroup\$
2
  • \$\begingroup\$ Depends on the cable thickness.. the thicker the cable the lower its resistance and the longer it can be \$\endgroup\$
    – Gilad
    Commented May 21, 2016 at 17:50
  • \$\begingroup\$ There are three possible distinct issues - ohmic loss in the power path, AC impedance of the power path, and transmission line effects on the control signal and its return. Each needs distinct remediation efforts - for example, wire gauge, point-of-load capacitance, and impedance matching. \$\endgroup\$ Commented May 21, 2016 at 18:19

2 Answers 2

1
\$\begingroup\$

There are many answers to this question. Some rely on starting over with good requirements.

  1. (As already stated) Thicker wires offer less resistance. Also CAT5 is a twisted pair cable and is best used to transmit balanced signals, not digital logic signals.

  2. Remote power supply for LEDs. Why not only connect data and ground back to the controller. And provide power to the LEDs local to the LED. Thicker wires are not as necessary as the current will be reduced. But caution will need to be taken to prevent ground loops!!!

  3. Consider buying LED strips with less demanding timing requirements. The strips you specify require signals with nanosecond accuracy. There are strips with separate clock and data lines which are likely more tolerant.

added later...

  1. Arduino boards are small. Consider locating the Arduino board closer to the beginning of the LED strip.

  2. Avoid powering the LED strips through the Arduino's own 5 volt regulator (if you are using 5 volt parts). Instead use a heavy duty (several amps) regulated 5 volt power supply and connect the LED power lead to the 5 volt regulated power supply.

\$\endgroup\$
4
  • \$\begingroup\$ Okay, let me try a thicker wire first and see how that works out before switching to a different led strip. I have a couple of lpd8806 laying around i can test with as well. \$\endgroup\$ Commented May 21, 2016 at 20:29
  • \$\begingroup\$ You probably only need the thicker wire for power and ground. If you still have the CAT5 cable you can double up the power and ground pins for this experiment. I think the 8806 strips can be clock at a slower rate. This will increase the latency but should increase the signal quality over longer cables. \$\endgroup\$
    – st2000
    Commented May 21, 2016 at 21:02
  • \$\begingroup\$ Slowing down the communication only helps with transmission line effects if it means that the receiver will rule out reflections, which is not necessarily true for a receiver capable of multiple speeds. \$\endgroup\$ Commented May 21, 2016 at 22:09
  • \$\begingroup\$ In faster signals that are under-damped ringing may introduce unexpected transitions. On the other hand faster signals that are over-damped have slow ramp up and down time. Causing missed transitions. Usually slowing down the data rate helps. Doesn't always but is usually one of the 1st things to try. \$\endgroup\$
    – st2000
    Commented May 21, 2016 at 22:10
0
\$\begingroup\$

Microphone sound cable does not work. The data signal is rising and falling so fast your cable act as a capacitor damping your signal.

Network cable CAT5 6 UTP can make your day - you have 8 cores, use two for +, three for - and one for DATA. Make sure your DATA is twisted with one of your - GND wires.

If you want to split to two LED stripes. You split with a buffer IC in order to reject reflections. To do that quite simply put two LEDS DS2812 in parallel close to the signal source and split from here.

To make sure your cable loss is small, put your LED on White RGB is all ON and measure the voltage to decide the voltage drop, and build a "local 7805 regulator" on your stripes and increase the voltage, and please put a buffer in, to protect your Raspberry Pi or Arduino, if the cable makes a twist and return voltage on your data line.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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