<br />On Tuesday, October 15, 2013 11:26 CEST, warpme <warpme@o2.pl> wrote:<br /> <blockquote>Marius,<br /><br />I think we can consider following hypothesis:<br /><br />1.USB transfer errors due RJ45 impedance mismatch compared to USB specs.<br />2.Non sufficient power supply due RJ45 cable resistance.<br />3.USB transfer errors due RJ45 cable cross-talks (with other cables).<br />4.USB data signals levels biasing due ground loops.<br /><br />Ad1: USB cables are called 'USB Cables' not only because they have USB connectors but also because they have correct wave impedance.<br />Impedance depends on frequency and there is high impedance difference because of ISDH freq ( order of 200kHz) and USB1.1 (multiple MHz).<br />So RJ45 will have wrong impedance for USB because of: 1\different spectrum of frequencies and also because 2\it is electrically designed for different impedance (ISDN requires 120ohm) while USBequires 90ohm.<br /><br />Ad2: USB requires given
resistance on +Vusb and GND not higher than.<br />RJ45 cable never was designed to carry high currencies required to power-up low-voltage devices like USB.<br /><br />Ad3: USB cable has practically always D+ and D- as twisted pair. Not only for achieving given impedance - but also for reducing sensitivity for external electro-magnetic fields which can cause induction of distortion signals in data path.<br /><br />Ad4: this is always problem when You have multiple power sources...<br /><br />Order of hypothesis I presented is IMHO from most probable to least probable.<br />For verification of them I propose however to go with following order of tests:<br /><br />Start with p2: use voltmeter on end USB device and check voltage.<br />If voltage is OK (not lower than 4.75V) - make sure there is no ripples by spikes of load.<br />Ideally will be to use oscilloscope. In You don't have one - simple add 470-2200uF electrolytic capacitor to filter ripples.<br /><br />When 2 not h
elps: test p4. Simply power-up ALL HW from single AC source. You can use temporarily AC power extender cable i.e..<br /><br />When this not help time is to eliminate p1+p3: try use dedicated, good quality of USB cable.<br />I would look in comp.store for special USB reach extending cable. You may choose at least USB2 supporting cable as they have to meet higher impedance requirements and consider to choose famous vendor (HAMA, etc)<br /><br />PS: I personally will start immediately with good USB cable as I'm pretty sure Your problem is with wave impedance mismatch....<br /><br />Good luck! </blockquote>Hi and thanks for the very detailed response. I think you're correct in your hypothesis except that I'm not sending USB signals over rj45 connectors. They are used only to extend the power source to the imon LCD. The reasoning was that all my cables should be easily detachable at each end for dismounting both the PC an
d peripherals. However. I think I learned my lesson about using only fit for purpose cables and connectors. I'm pretty sure that the current-draw of the lcd backlight is too high for the signal cable and connectors and that there's not enough power left for the IR receiver to work reliably.<br /><br />Will find some fit for purpose shielded poser cable this evening and connect using good old-fashioned choc-strip.<br /><br /> Thaks to all for the very helpful response throughout the thread. I really appreciate it.<br /><br />Cheers!<br /><br />Marius<br /><br /><br /><br />