Re: Powering the Raspberry & TNC.
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,
--- 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.
> 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
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:
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:
>> 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:
>>> 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
> 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...