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Thread: Buffer/line driver - null pixel without pixel

  1. #21
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    Default Re: Buffer/line driver - null pixel without pixel

    Not to take away from RobG's device - but if you look at the uAmp mentioned earlier, the developer has some scope output from his device showing how it works - basically it just 'squares' up the ugly signal coming in - perhaps using some Schmitt trigger or something - not sure... quite interesting though - simple device anyway!

    Brian

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  2. #22
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    Default Re: Buffer/line driver - null pixel without pixel

    I ordered a few of the uAmp's just for this... Was assuming from the uAmp writeup it was a Schmitt trigger but he said it can be used for 5V or 12V so not sure...
    For $1.50 Rob's would be quite a bit cheaper than the $4.65 in the coop though.
    -Chris

    2012: 3 Renard SS24's for 72 channels... 6236 lights... powered by HLS
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  3. #23
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    Default Re: Buffer/line driver - null pixel without pixel

    The uAMPs may not not come in until October. If we can get this this going we could have these by September.

  4. #24
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    Default Re: Buffer/line driver - null pixel without pixel

    what would be the best way to enclose these if they're out in the yard? I have a few long runs between my sections where these would come in handy. I'm in for 20

  5. #25
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    Default Re: Buffer/line driver - null pixel without pixel

    Good question. I was thinking to use Ray's pigtail sets and use a tube with caps or a plastic/alum box as enclosure. I would also use cable glands similar to those used on floods.

    Something like this could work, but I am not sure we could squeeze the board through one side.
    Last edited by RobG; 08-05-2015 at 11:35 PM.

  6. #26
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    Default Re: Buffer/line driver - null pixel without pixel

    BTW, regarding uAmp demo video, that is some awful ringing. However, it could be cased by the test environment itself (oscilloscope setting, probe calibration, power lead inductance, probe's ground lead, reflection caused by inductance, etc.)


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  7. #27
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    Default Re: Buffer/line driver - null pixel without pixel

    A quick note on ringing. All wire has a capacitance per foot and inductance per foot. A wire that is basically open (high impedance) on the far end has a resonance and this is the basis of standing waves on a transmission line. Guys that work with RF is familiar with this. This for example is why car ignition has that same ringing after the spark goes out, the wire end is open and the circuit rings generating RFI in the AM radio. To reduce the RFI, (Radio Frequency Interference) resistive wire, ferite bead wire, and other suppression techniques are used to absorb the energy. This is exactly why solid core spark plug wire is not used.

    Unfortunately adding suppression to a long wire kills the signal. However, terminating the wire into it's nominal impedance also kills the ringing. This is the basis for all Network wire, RS485 data including DMX512, and radio and TV coax transmission line.

    The normal problem with terminating a transmission line for Pixels is the signal driving the line in most cases is LOW POWER so the termination simply kills the signal too low to be detected properly at the pixels. Pixels do not have low Z high current drivers on the output. Many Pixel controllers use just TTL or even the Propeller chip output pins without a driver to drive a low impedance data line properly.

    One of the reasons I selected the DIYLED Express DMX bridge is because it does use a true differential RS485 driver IC on the outputs. I haven't had the time to experiment, but it is on the agenda as time allows, is to drive a wire pair in a CAT 5 cable with the differential data and terminate it after about 200 Feet, and feed the Data + directly into a pixel string. I have verified that WS2811 pixels are high input impedance. In theory this should keep the data clean to the far end of the wire with no ringing and a clean signal to pixels with a local power supply for the string.

    Unfortunately real life is in the way as I am dealing with my wife's cancer. It's back. That is the priority as it should be. Currently working full time, and chief cook and bottle washer, laundry, yard work, taxi driver, etc is a full schedule. Not doing much with pixels at the moment.

  8. #28
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    Default Re: Buffer/line driver - null pixel without pixel

    Quote Originally Posted by Technician View Post
    A quick note on ringing. All wire has a capacitance per foot and inductance per foot. A wire that is basically open (high impedance) on the far end has a resonance and this is the basis of standing waves on a transmission line. Guys that work with RF is familiar with this. This for example is why car ignition has that same ringing after the spark goes out, the wire end is open and the circuit rings generating RFI in the AM radio. To reduce the RFI, (Radio Frequency Interference) resistive wire, ferite bead wire, and other suppression techniques are used to absorb the energy. This is exactly why solid core spark plug wire is not used.

    Unfortunately adding suppression to a long wire kills the signal. However, terminating the wire into it's nominal impedance also kills the ringing. This is the basis for all Network wire, RS485 data including DMX512, and radio and TV coax transmission line.

    The normal problem with terminating a transmission line for Pixels is the signal driving the line in most cases is LOW POWER so the termination simply kills the signal too low to be detected properly at the pixels. Pixels do not have low Z high current drivers on the output. Many Pixel controllers use just TTL or even the Propeller chip output pins without a driver to drive a low impedance data line properly.

    One of the reasons I selected the DIYLED Express DMX bridge is because it does use a true differential RS485 driver IC on the outputs. I haven't had the time to experiment, but it is on the agenda as time allows, is to drive a wire pair in a CAT 5 cable with the differential data and terminate it after about 200 Feet, and feed the Data + directly into a pixel string. I have verified that WS2811 pixels are high input impedance. In theory this should keep the data clean to the far end of the wire with no ringing and a clean signal to pixels with a local power supply for the string.

    Unfortunately real life is in the way as I am dealing with my wife's cancer. It's back. That is the priority as it should be. Currently working full time, and chief cook and bottle washer, laundry, yard work, taxi driver, etc is a full schedule. Not doing much with pixels at the moment.
    Sorry to hear about your wife, I wish her all the best! I hope things work out Ok.
    As a side note, I love to read your explanations, very informative.

  9. #29
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    Default Re: Buffer/line driver - null pixel without pixel

    a simple board using a max485 chip is the answer. 8 pin chip with an output enable pin. I've made 1 cable so far. Signal goes into tansmitter then over twisted pair cat5/6 to the receiver. power to run the chips also goes over the cat5 cable. What I haven't tried yet is to see if 3 signals can go over one cable. Roger

  10. #30
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    Default Re: Buffer/line driver - null pixel without pixel

    Will this be able to increase the distance to the next pixel at all? In other words if I have to put one at 25 feet because of signal loss...will I gain any distance to the second over 25'?

    Sent from my LG-H811 using Tapatalk

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