Re: ATM Brightness of LED

["Bob May" <bobmay@nethere.com>]

Dominic wrote:
<<
Excuse me, there were two posts so I did not follow this...
Were you saying you prefer a voltage regulator as I mentioned or
current regulation as Richard proposed? Both are possible. I know
voltage regulators to work...
>>
Actually, I was pointing in a different direction.  The 9V battery holds its
voltage as well as the other batteries do but the larger resistor in series
migitates the voltage change and thus makes the LED more constant in its
output.  When the 9V battery finally hits its end of life, the final voltage
drop is a lot more viewable over a short time period, especially if you are
using the LED only for short periods of time.
In addition, it is a lot easier to get a wall power supply (wall wart) for a
voltage like that than trust a 3V supply to stay close to its voltage along
with the fact that a 9V battery connector can be used to hook to another 9V
battery connector and thus allow the usage of a battery or AC power a choice
to make for the location and thus save on the usage of those expensive
batteries.
Using a voltage regulator (there are nice switching regulators that can be
used with a single cell if so desired) can provide a nice constant voltage
for the LED until the final end of life when the regulator just won't
regulate any more.
The constant current regulator is also doable but the voltage needed to run
such a device will require a 9V battery at the minimum.  Again, the current
will stay constant (and thus the voltage across the LED) until the regulator
falls out of regulation.  I'll note that the higer resistance used with the
9V wiring design is a crude regulator of the current as the current change
with that higher resistance is less than with the 3V battery setups.
All different ways of keeping a LED output bright until the battery is
exhausted.  I'll note that a fresh alakine battery has about 1.7V of output
and they are considered dead at about .9V or so.  That is a wide range when
the resistor is of a small value as the 3V battery setups have.
Hope this clears things up for you!
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net