RE: CCTV

["Keith Doxey" <ukha@xxxxxxx>]

If you are using a 12V supply then anything between 510R and 2K. (510R will
give you about 20mA through the LED so it will be nice and bright if you
are
using it as a blown fuse indicator. If its going t  be "supply
healthy" and
on all the time then 1K or 2K would give a dimmer LED although any of the
resistors in that range will be fine.

Keith

> -----Original Message-----
> From: Brian G. Reynolds [mailto:brian.g.reynolds@xxxxxxx]
> Sent: 29 July 2001 22:28
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] CCTV
>
>
> Keith, what rating LED and resistor should I use?
>
> B.
>
> > -----Original Message-----
> > From: Keith Doxey [mailto:ukha@xxxxxxx]
> > Sent: 29 July 2001 15:53
> > To: ukha_d@xxxxxxx
> > Subject: RE: [ukha_d] CCTV
> >
> >
> > Hi Brian
> >
> > > > Depends on the camera. If it has onboard voltage
regulation
> > > then it should
> > > > be OK. If not you may kill it. Also even if it has
onboard voltage
> > > > regulation, dropping the extra voltage willl generate
quite a bit
> > > > more heat.
> > >
> > > Is there anyway to tell this? so by dropping the voltage it
> > generates more
> > > heat? even just 3v?
> > > is the opposite true as well? give it more voltage and it
turns int  a
> > > fridge..............
> > > complicated this lecky stuff........
> > >
> >
> > Quick example.
> >
> > Although the original PSU is 12V @ 300mA, the camera is possibly
> > a 9V camera
> > drawing 300ma which will have a built in voltage regulator. The
Voltage
> > Regulator will be dropping 3V @ 300mA which is 0.9W or 900mW of
heat
> > disipated by the regulator. If you use a 15V power supply then
> > the regulator
> > will drop 6V @ 300mA  = 1.8W Whilst the actual regulator may be
> rated for
> > that power the heatsink may not be able t  dissipate enough of
> > the heat and
> > the whole camera will run hotter than it should. Heat is the
> > biggest killer
> > of electronics.
> >
> > > Could I therefore take a feed from the PC PSU and feed it t 
all
> > > the cameras
> > > at the same time?
> > > I was originally going t  put an extension lead with all the
> > PSU's plugged
> > > int  it and use an appliance module t  switch the extension
> lead but not
> > > sure if it will all fit in the same case, heat might also be
a problem
> > > although I could fit a high-speed cooling fan, I have
another
> > tray to try
> > > just this.
> > >
> >
> > A typical PC power supply can supply over 8A @ 12V. Thats enough
for at
> > least 24 cameras.
> >
> > > What is a wall wart? is it just slang for all PSU's that
plug
> > > int  the wall
> > > and look hideous?
> > >
> >
> > You got it :-)
> >
> > > Would it be a good idea t  buy a PSU for this job?
> > >
> > > What fuse should I use? presumably in line with the power
cable in a
> > > in-holder?
> > >
> >
> > Neatest way if you are rack mounting is to fit panel mount
> fuseholders on
> > the front panel.
> > If you put an LED and resistor across the fuse it light if the
> fuse blows
> > indicating a fault, or you can put an LED on the outgoing side
> of the fuse
> > to show the supple is present.
> >
> >
> > FUSE BLOWN INDICATOR
> >  +ve --------fuse------------------device--0V
> >
> > 	   --LED--Resistor---
> >
> > or
> >
> > SUPPLY HEALTHY
> >   +ve --------fuse------------------device--- 0V
> >
> >                     --LED--resistor-------- 0V
> >
> >
> > >I have also bought a 4U case to try and fit my Server int ,
but
> > this needs
> > a
> > >lot of thinking, something I am loathe t  do on a hot day
like t day.
> >
> > My original thoughts for doing this were get a Minitower. Remove
> > the cover,
> > lay it on its side inside the 4U case. Slide the CD & Floppy
> forward, draw
> > round them t  mark the rear of the front panel, cut the holes
> and bolt it
> > all together. By fitting a "normal" chassis inside it
it means
> > any PC config
> > changes are easy t  do.
> >
> > I have now decided to use Desktop cases and just use Aluminuim
angle as
> > rails to support it in the rack. Short pieces of angle ali as
fixing
> > brackets pop riveted to the sides of the lid will hold it in
> place in the
> > rack as the weight would be taken by the rails fixed to the sides
of the
> > rack. My Jukebox is a desktop machine and just measured it....
> 17.2 inches
> > wide so it will fit snuggly between the 19" rails,
5.25" high so its 3U.
> >
> > > Sorry for all the questions but you guys are soooooooooooo
clever!
> > >
> >
> > We've also learnt a LOT from past mistakes :-(
> >
> > Keith
> >
> >
> >
> >
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>
>
>
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