tag:blogger.com,1999:blog-7275378574543326675.post6830452868617591226..comments2024-02-02T09:08:43.286+00:00Comments on Astro-Beano: Power Over Ethernet for Raspberry PiPeter Cockhttp://www.blogger.com/profile/00233221181317137855noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-7275378574543326675.post-22251906181127968862014-08-10T04:12:06.659+01:002014-08-10T04:12:06.659+01:00no need to do difficult with poe adapters as you...no need to do difficult with poe adapters as your ethernet connection only use 4 wires(1,2,3,6) the remaining 4 (2 pairs) you directly connect to the 5v reducing the voltage drop significantly.<br />measure the resistance of your cable before connecting the rpi, you need to supply at least 1.5Amp (1.2 rpi, 140mA for webcam and some headroom)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7275378574543326675.post-20645492058865096902012-09-05T00:19:26.682+01:002012-09-05T00:19:26.682+01:00Hi Tim - thanks for the detailed comment. I don...Hi Tim - thanks for the detailed comment. I don't have an oscilloscope but I have now found my electronic multi-meter so will be able to take some voltage measurements. I have also ordered a DC/DC step down converter (nominally 12V to 5V for use with a car battery or similar) which should let me apply extra voltage to the head end.Peter Cockhttps://www.blogger.com/profile/00233221181317137855noreply@blogger.comtag:blogger.com,1999:blog-7275378574543326675.post-33840300718512942842012-09-04T23:37:16.121+01:002012-09-04T23:37:16.121+01:00I should have added to my last comment, switchmode...I should have added to my last comment, switchmode PoE at higher voltage carries the added advantage of supporting the same power draw with a lower current.<br /><br />The main trick, then, is selecting a regulator with sufficient output current. I note the regulator in my link supports 600ma, and it has a 1.3A big brother at the manufacturer's website. The 1.3A version would seem safer in this application.<br /><br />The regulator could be added inline with the PoE extractor, rather than replacing the onboard regulator. In this scenario, however, it'd be highly beneficial to add a bypass wire to the onboard regulator.wookiehttps://www.blogger.com/profile/07691788417329476872noreply@blogger.comtag:blogger.com,1999:blog-7275378574543326675.post-81231913481094275142012-09-04T23:23:34.604+01:002012-09-04T23:23:34.604+01:00Perhaps you already understand this, but -
It'...Perhaps you already understand this, but -<br />It's worth bearing in mind that, as you've expected, voltage drop occurs over longer cable runs. The trick, though, is that it's likely to increase while higher current is being consumed, possibly causing difficult-to-diagnose behavior.<br /><br />If you had an oscilloscope you'd be able to see the end voltage briefly dipping under 5v during such events.<br /><br />The usual solution in more-fancy PoE arrangements is to push some extra voltage at the head end, and regulate it down to the target voltage at the destination. Since the raspberry pi does include a voltage regulator, this matches what you did in the 30m update, and most likely the USB devices introduce current spikes causing further voltage drops.<br /><br />Although you want to be careful pulling too many volts+amps through a linear regulator, you could try using a switchmode regulator instead if it can withstand an input voltage of (say) 13 or 20 volts:<br />http://hackaday.com/2012/07/07/another-switch-mode-regulator-swap-for-the-raspberry-pi/wookiehttps://www.blogger.com/profile/07691788417329476872noreply@blogger.comtag:blogger.com,1999:blog-7275378574543326675.post-3241447135309018362012-08-15T17:54:54.524+01:002012-08-15T17:54:54.524+01:00Great blog, I'm hacking my Logitech 500 webcam...Great blog, I'm hacking my Logitech 500 webcam with a mic, IR LEDs on order, will be using a RPi, Motion for recording later on. I'm testing the webcam with IR LEDs from my laptop first using motion to record any movement and sound.Anonymousnoreply@blogger.com