I’m still getting a fair bit of corruption.Re calculating the impedance,
don't try ,
its going to have way to many variables
experiment is goinn to be your best option.
To be honest, that signal at the receiver does not look to bad.
I assume thats with the leds plugged in.
That shoudl work just fine..
The errors are random. Sometimes a single LED anywhere will flash. Sometimes a a few LEDs in a bunch will flash. Sometimes when I’m animating a white flicker (each LED dims in and out gently), all LEDs will briefly flash a different colour. It’s quite random.What you are doing is adding an impedance, which works with the system impedance , and adding a filter .
At the sender end, assuming you have a series resistor at the transmitter,
if you put a capacitor across that resistor, it lets more high frequencies through , giving a faster rise / fall time.
if you put a capacitor from the output of the resistor at the transmitter to ground, you are attenuating the high frequencies, resulting in slower rise / fall times.
your signal as shown at the receiver looks fine,
I understand you have led strips in series,
did you say the first strip works ok, the follow on strips have problems ?
From what I have seen, the wires are not twisted, or even "together" they are just buried in walls, and strung along other bits of wall.The capacitance can be estimated from the separation of the two wires. The inductance can be estimated from the length of the wire. There are some calculators on the web which may help, as the dielectric of the wire insulation will have an effect.
As a rough guide, twin cables will be in the region of 100-300 ohms (only approximately, could be more or less). A 3k resistor may attenuate the signal that reflections are not "seen" by the receiver. Your 330 ohm may not attenuate the signal enough, but this all depends on the sensitivity of the receiver. Likewise your 1M scope probe capacitance would have attenuated the reflections enough but 10Mhz reduces the capacitance to about 10pF and not provide attenuation.
The root cause is the reflections. If you can still access the two ends (first LED and transmitter?) and send a short regular pulse down the wire the reflection time will give you the characteristic impedance if you know the length of wire. Then the best way to reduce the reflections is to try to load the receiver (if you can do this) with the impedance. If you can still access the end of the long wire or a point nearby try loading it with a parallel 100-300 ohms (experiment a bit). From what you say it seems the receivers should work with a reduced signal and you just need to attenuate, or, as we are trying, to eliminate the reflections.
What are the input and output specs of the tx-rx? Often RF stuff works at 50 ohms. I'd anticipate having to use a 51 ohm terminator but your line may need to be matched to that to prevent new reflections but you may "get away" with some intermediate loading.
@crutschow So - select the parallel receiving end resistor first.Try various values of resistors across the cable output to ground (not in series) and select the one that gives the best waveform.
Hey,@mriksman I'm having almost identical problems to you - I split a length of LEDs and join the end of one half to the start of the other half.
My question is about what resistors and configuration you used at the transmission and receiving ends? I know it will need experimentation but I'd like to know what order of magnitude to start with.
My setup is as follows:
I use a single strand of cable from the end of one directly connected strip back to the control board (2.2m) and then 3 cores of a 6-core cable to take power and the signal to the other strip (3m). That signal is the full 5v re-amplified from the last LED.
If I take the extended signal via a single core cable (even in a tight 10cm diameter coil)... it works. If I hold the single core coil tightly close to the 6-core wire or any other wire I get corruption. I think this is a capacitative effect and my problem is due to using multi-core cable. If I run the power through one multi-core cable and either use a single or twisted strand of cat5 I still get corruption.
I don't have a scope so all I can do is observe.
Thanks - I'll start thereHey,
I ended up with 680ohm resistor in series with the data line just before Din on each strip. A scope will help tell you if you have too little (spikes/oscillations) or too much (you get a square-ish wave but it starts getting rounded edges).
Yes, I'm aware that I should use a single reference ground and I only use 1 PSU for my Pi and the LEDs but I'll bear that in mind for the future.I also have issues with running long, separate power cables to sections of strips. I run 4x cables, each powering 4x strips each. But between each ‘transition’ (Strip 4 of Power 1 to Strip 1 of Power 2 for example) I get a lot of issues. So if you do something like this, make sure you connect the GND of each LED strip; even if the power feed is separate. Keep those strips’ GND tied together.
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by Jake Hertz
by Jake Hertz