>From: Frank van Lindert <lindertv@xxxxxxx>
>
>On Tue, 15 Dec 1998 13:37:06 -0800, Jan Steinman <jans@xxxxxxxxxxx>
>wrote:
>
>>To Frank's circuit, I'd like to add that you SHOULD NOT neglect the output
>>capacitor...
>>I'd also suggest adding a 0.1uf ceramic capacitor to the input lead...
>
>I agree with you Jan, that these caps are wisely added in adverse
>conditions. But when using a 6 or less volt battery (and not an AC
>sourced power supply) for input with no other equipment connected at
>all, what can go wrong? Would the cable pick up enough noise to be
>amplified by the IC to an unacceptable level? The batteries themselves
>are doing well as a very big capacitor on the input side .... or
>should the original Olympus 3V battery pack have a capacitor added as
>well?
I don't believe the original Olympus cable had active electronics -- it was
direct feed from batteries to the camera.
The addition of an IC regulator may exascerbate problems that wouldn't
appear in the simpler arrangement. It contains an amplifier that can
oscillate under certain conditions, such as a small spike on the input
combined with a resonance on the output.
The battery is indeed a "big capacitor," but at cell phone frequencies, it
is many wavelengths away from the IC with just a few feet of cord! It is
possible for a cell phone to induce a momentary spike in the IC that can
damage it or cause it to oscillate.
Of course, I agree that these circumstances are not likely -- I'm just
pointing out that electrical engineering "best practices" are to bypass all
IC power leads, and that the IC manufacturers' themselves recommend this
practice. It is cheap insurance!
More cheap insurance: once you go to the trouble of building this thing,
you'd hate to accidentally destroy it. Put a 1/10th amp fuse in series with
the input lead, and a diode "backwards" across the input and ground. This
will blow a cheap fuse in case the polarity is reversed, rather than
blowing your regulator IC and possibly your camera. Not worried about
backwards polarity? Do you ever loan your equipment, or have a helper?
("Hey honey, can you put fresh batteries in all the photo gear so I'll be
ready for this shoot?: :-)
If extremely cost-conscious consumer electronics gear (like $30 CD-players
or even $10 tape recorders) have bypass caps and fused inputs, shouldn't
you?
: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229
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