Is there a CMOS op-amp with low
noise, good common-mode isolation,
and unbalanced output available? I
would like to use it in a loop antenna
preamp in a location that has an
extremely high power-line noise level.
E-mode whips with a preamp are
definitely unusable. This antenna
would be untuned and intended for
use below 30 MHz.
#9141 John R. Seeley KI4LTB
Palm Bay, FL
UV LED VS UV Bulb
I'm been working a lot with high
power LEDs now that they're so affordable. I'm especially fond of the UV
LEDs for visual effects at night, but I've
heard that some UV LEDs can cause
blindness, and that I should use a UV
bulb to create the effects. Is this true?
Can someone explain the difference?
Ft Wayne, IN
Is there such a thing as a noise
cancelling technology that would
allow me to play my guitar without
disturbing the neighbors?
I get complaints about noise from
my apartment when I play. I just can't
use headphones and I've tried putting
blankets on the wall for soundproofing, but I still get complaints.
How about an electronic solution?
#9143 Brian Tate
[#7143 - July 2014]
I'm thinking of building a solar
charger for my iPhone, but don't know
how to handle the internal lithium
battery in terms of taper current, etc. —
especially when I have the phone
on all day. What I've found online is
information on charging disconnected
lithium batteries, not ones under load.
#1 Charging your iPhone should
not require any special accommodations. The OEM charger from Apple
supplies 5V at 1A via a USB connection with proper cable. Either the
30-pin connector or the new five-pin
"lightning" connector cable both deliver the same power.
The phone (as all phones now)
has built-in current limiting, temperature sensing, and voltage sensing to
protect the battery.
You just need to deliver 5V
regulated to the cable with, of course,
polarity protection for the solar charger. A simple LM7805 regulator IC is
what most chargers use for the 5V.
It really is NOT a good practice to
leave the phone on the charger
continually, as most rechargable
batteries 'like' to be exercised. Charge
it up, let it run off the battery until it
shows recharge is needed, then
reconnect the charger. You should get
several years of service from it.
Scott City, KS
#2 First, under load shouldn't be
that much different from being off as
long as the circuit can handle the
current needed to do both jobs. That
you will need to measure and then
find a pre-built circuit to do the trick.
I suggest pre-built since they are
so cheap. I did the same kind of thing
for a phone that refused to recognize
its own charger as a valid charger. A
good 'ol Motorola phone; I'll never
buy another phone that has some
type of recognition routine in it to
check the charger.
In any event, the first thing I
noticed was that my camera charger
was for the same type of battery, same
voltage, same Ahr rating, same Li Ion
battery. I hooked up wires from the
charger into the phone and it worked
Next, I wanted a more universal
Li-Ion battery charger and found more
than one online. The one I settled on
was from dx.com:
1A Lithium battery charging
module - blue $1.70/e
There are others as well;
a red module at 3A for under $9
These are circuit cards usually
with a USB power port to give it 5V/
1A to work with, so you will need to
do some soldering for connections to
the battery from the board.
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94 September 2014