Re: Serial cables & power supplies
Andrew (adunn@minyos.its.rmit.EDU.AU)
Sun, 17 Nov 1996 16:48:54 +1100 (EDT)
On Sat, 16 Nov 1996, Jeff Hinman wrote:
>
> Hi Andrew.
>
> With help from Jon Reinberg, I posted a design of my AC adapter for the Omnigo.
> I'm not sure what you mean by 3volt plug pack. Is it an adapter shaped like two
> AA batteries in series?
>
> Concerning the ripple effect. Yes, there have been noted problems. I have been
> in contact with an Omnigo user concerning that. She is using a PCMCIA Megahertz
> modem with an AC adapter in the Omnigo and is experiencing ripple effect. If
> she uses the batteries, they work for only 5 minutes (the current drain is high
> at 1.2A or 1200 mA). When a 2A 3.0V Tektronics power supply is used, the Omnigo
> acts weird. This is most likely due to ripple. I would suggest using the
> cleanest power source you can design/buy.
>
> I normally suggest the Radio Shack 3/6V 700mA AC/DC adapter. It is a regulated
> power supply that provides "hum free" or rippleless use. If you are using a
> modem or a card that causes the Ominigo power use to increase, I would suggest
> using some other kind of regulated, high current supplying power source.
>
> Jeff Hinman
> ust941@edcca4.bgl.ca.boeing.com
>
Thanks for your advice Jeff. Since writing I have built my voltage
regulator, which converts my 12 volt AC adapter down to 3 volt DC. I have
tried it in my OGO and it seems quite happy -> the bios battery check
reported 2.95volts. (although voltage measured with a voltmeter across
the terminals said a little over 3) Sometime this week I intend to
measure the voltage waveform with a CRO to see the voltage waveform, and
if the voltage ripple has been removed. I don't own any modems/PCMCIA
cards at the moment so am unable to check them out.
My design incorporates your "battery adapater" attached to the circuit's
output. It _should_ (hopefully!) be able to supply high current drain,
even as high as 1.2A as you mentioned.
As to people having trouble with ripple with their 3volt packs, I have a
simple suggestion (please correct me if I'm wrong) -> try wiring a nice
chunky capacitor across the battery adapter terminals. This should
smooth the ripple somewhat.
And finally, my idiot's tip for the day -> don't solder while wearing
shorts. (Luckily the molten solder stuck mainly to my hairly legs, not my
skin! ;-)
**************************************************************************
** Andrew Dunn **
** **
** adunn@minyos.its.rmit.edu.au **
** **
** http://minyos.its.rmit.edu.au/~adunn **
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