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Re: Powering the Raspberry & TNC.

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  • Stephen
    Roger, I use the same module, but I clean up the output by passing it through a LM2940 3 leg 5 volt LDO regulator (with the caps each side as you would use for
    Message 1 of 53 , Apr 5 3:06 AM
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      Roger,

      I use the same module, but I clean up the output by passing it through a LM2940 3 leg 5 volt LDO regulator (with the caps each side as you would use for a standard application). I don't have any objective measurements but the data sheet quotes an output noise voltage of 150 uV. The whole lot fits into an altoids tin.

      Hope this helps,

      Steve G0XAR

      --- In Raspberry_Pi_4-Ham_RADIO@yahoogroups.com, Ian Bennett <ibennett@...> wrote:
      >
      > Hi Ray,
      > I think I have the same type and managed about 2A (ish) output at 5V
      > with very respectable ripple (read: hardly noticeable on the cro). I was
      > a little disappointed seeing the output at 4.85V but was withing spec.
      > I have been bitten a few times because I didn't read the data sheet
      > correctly, so I read the thing many many times whilst waiting for mine
      > to arrive.
      > The one thing (ok, there was two) that stuck in my mind was the use of
      > low leakage electros and the low loss "tracks" required )shown in bold
      > in the recommended circuit).
      > I built mine on vero board and the the low loss connections were
      > constructed using additional tinned copper wire following the copper and
      > a heap of solder to fill the gaps. If nothing else, it won't blow away
      > in the wind ;-)
      > My coil came out of a few trashed UPS'. I was ratting them for the
      > toroids but luckily I kept a few intact.
      >
      > Ian
      >
      >
      > On 05/04/13 08:51, Ray Wells wrote:
      > >
      > >
      > > I bought 5, smps adjustable output modules using the LM2596 from Ebay
      > > ($1.52 each including freight from Hong Kong to Australia!). These are
      > > branded Leivin and the PCB layout and circuit is as per the National
      > > Semi datasheet. A preliminary test with a 1A load showed a very noisy
      > > output on the CRO. When time permits I'll try the NS recommendation of
      > > an LC filter in the output. I think the device has potential but not
      > > "off the shelf" for running the RPi.
      > >
      > > Ray vk2tv
      > >
      > > On 05/04/13 00:58, Roger Elmore wrote:
      > >>
      > >> Charles wrote:
      > >> > I am looking at another device to replace the converter because
      > >> > this device is not adjustable and is set for 5 V. I need to
      > >> > increase that to 5.25 to compensate for the drop across the
      > >> > polyfuse.
      > >>
      > >> I've begun collecting the parts for a pair of PI+TNC-PI combos (for an
      > >> APRX digi/IGate and a Linux RMS Gateway) in a rack mount case powered
      > >> from the same Astron RS-50M as the two radios and going to give the $7
      > >> LM2596 module (bought from Amazon) a try. 3-40V in and 1.5-35V out at
      > >> 3A. My plan is to use a separate LM2596 fused at 1A for each PI's
      > >> input, with a 6A rear panel accessible fuse common to the 13.8V input
      > >> of each LM2596 and a 80mm fan. Here goes nothing...
      > >>
      > >> On a different note, has anyone experimented with light pipes to bring
      > >> the PI's LED status to the front panel of a chassis? I've used the
      > >> Bivar SLP3-450-100-F on a NHRC Micro repeater controller previously
      > >> but the LEDs on the PI are too close together for those. I was looking
      > >> at the flexible Bivar LC-2.0 at the Mouser website and was wondering
      > >> if those might work. Any input from anyone?
      > >> --
      > >> Roger KJ4AJP
      > >>
      > >
      > >
      > >
      > >
      >
    • Jim Thisdale
      F.Y.I. Most computer mother boards have switch mode regulators on the board to make all the various voltages needed for the processor(s), memory, north & south
      Message 53 of 53 , Apr 14 11:38 AM
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        F.Y.I.

        Most computer mother boards have switch mode regulators on the board to make all the various
        voltages needed for the processor(s), memory, north & south bridges, and various other hardware.
        Gamer & enthusiasts boards often tout how many regulators/phases they have.

        As for radiation, most of the noise is from the leads & tracks on the board of chips themselves,
        especially when they are unshielded. A 5, 3.3, or even 1.8 volt signal toggling on-off at a high
        rate can radiate quite a bit, with 32 or 64 bits wide all toggling at such high clock rates it will
        radiate a lot of hash.... Computers tend to generate & radiate a lot of hash that's one reason the
        better made ones have metal cases and metal shielding in key areas. The minor amount of noise/ripple
        out of the supply is miniscule compared to the hash from the computer it-self. If a supply is truly
        that noisy the noise/spikes on the power would be mistaken for data and foul up the processing.

        -Jim- N1JMM, KB1YPL_B
        Visit my Pi running ircddb, dvrptr, Apache & many other things:
        http://n1jmm.no-ip.org

        On 4/7/13 6:15 AM, JJ wrote:
        >
        >
        > On 13-04-07 05:49 AM, John B. Cundiff Jr. wrote:
        >> Every time any digital device switches from off to on it produces a small spike and every spike
        >> as harmonics or RFI ... you can never completely clean up the supply of a computer ...you must
        >> design the computer
        >> to live with the spikes and RFI.
        >> On 04/07/13, Ray Wells<vk2tv@...> wrote:
        >>
        >> John,
        >>
        >> It's more than just spikes.
        >>
        >> The National Semiconductor recommendation to "tame" the output of the LM2596 smps is to add a
        >> series inductor (10mH from memory) and a shunt capacitor. Whilst this may very well result in a
        >> power supply that will "please" the Pi, it will do absolutely nothing to suppress RFI, which
        >> requires techniques quite different from those that produce a clean DC supply. The problem is not
        >> insurmountable but would require some devotion to produce a supply that is both DC and RF clean.
        >> It can be done.
        >>
        >> FWIW, the problem, from a Pi perspective, isn't necessarily spikes. Some smps's produce a distinct
        >> sawtooth output under load and whilst there may not be any spikes, there may well be dips below
        >> the minimum working voltage of the Pi at the bottom of the sawtooth waveform.
        >>
        >> Don't believe for one moment that you can assess a supply as being "good" with a voltmeter,
        >> digital or otherwise. It is indeed a case where a picture is worth a thousand words and that is
        >> where the CRO plays its part. If you don't have a hardware CRO, use a soundcard based device.
        >> There is plenty of free oscilloscope software available online.
        >>
        >> Ray vk2tv
        >>
        >>
        >>
        >> On 07/04/13 18:03, John B. Cundiff Jr. wrote:
        >>> Wood not a simple choke ...maybe a torridal choke
        >>> suppress the spikes every one is worried about .
        >>> Put a big value filter capacitor afterwards .
        >>> Be a lot more portable .. simpler and ..eleganter etc.
        >>> On 04/06/13, Kerry McKenzie<kermck@...> wrote:
        >>>
        >>> Guys
        >>> a rarely dumb question?
        >>> how hard is it to just get an old pc power supply AT or ATX ,.... who
        >>> cares either way,... you will get between 15 and 50 amps at 5 volts and
        >>> throw a couple of caps across it.
        >>> If you crow it,... it will be smooth
        >>>
        >>> if you go to any computer repair shop they will possible give you as
        >>> many old ones as you want as most of them still work.
        >>> i have 4 or 5 in my workshop down stairs and use them for all sorts of
        >>> things and it so easy.
        >>>
        >>> my 2 cents worth.....Kerry
        >>>
        >>> PS Linux is still a bitch and I,m going nowhere with my projects ;-((
        >>>
        >>> --
        >>> Kind Regards
        >>> Kerry McKenzie
        >>>
        >>> PO Box 4492
        >>> Kirwan QLD 4817
        >>> Australia
        >>>
        >>
        > yes, I agree...I use a vp-1020 satellite card in my computer and the P.S. noise is affecting the
        > sensitivity of the card....my ham antennas are more than 100 feet from the house due to the rf
        > racket produced by many switching power supplies in the house...even the darn router and cable modem
        > supplies were awful, so running as much as I can directly from my solar system 12v rail...but there
        > are just so many things nowadays that use these switching supplies it's hard to eliminate them
        > all...oh, and then there's a neighbors samsung plasma tv .. 300 feet away from here and it wipes out
        > my packet system when it's on...
        > grr...
        >
        >
        >
        >
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