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92 February 2009
I am building a project that uses a
0-100 UA meter. Can I purchase a
DATEL/MURATA 0-199.9 UA digital
meter (LED) and use it in place of an
analog style? I realize that I have to
power it separately.
Can a USB speaker — like a
Harmon Kardon iSub 2000 — be
rewired to use a regular audio input
while still using the built-in amp?
#2092 Jerry Williams
West Bend, WI
Power Pac for HO Railroad
Does anyone know of any plans
for controls to run several trains
simultaneously on the same line,
independently of one anothe?
#2093 Terry Murphy
El Cajon, CA
Regulators or Zener Diodes?
Many of us use the regulator
devices 7805, 7812, etc., in our designs.
What is the difference between these
and using zener diodes? An internal
circuit diagram would be helpful! When
do you use a low resistance resistor in
series with these devices?
Auto 12V to Laptop 19V Power
I’m looking for a circuit that can
boost the 12V in a car to 19V, enough
to run two laptops (batteries removed).
It will have to provide at least 100W. I
bought one off eBay but it is unstable
with my laptops (shuts down randomly).
Constant Current 30 VDC
I need a schematic for a 30 volt
DC power supply running at a constant
current of 800-900 microamps,
I want to make colloidal silver of
minimum particle size and the current
flow through the solution must not
exceed one milliamp. In the beginning,
the resistance is very high through
steam distilled water, but in time
the resistance becomes progressively
lower. The adjustable current flow must
be held constant by the supply.
#2096 Phil Vogel
Sensing AC Fan Motor
I’m looking for an easy way to
sense when my home AC/heater fan is
running (110 volts).
I have an electronic timed pump air
freshener that I want to spray into the
AC/heater plenum ONLY when the fan
is running so it will carry the fragrance
throughout the house.
#2097 Porter Sadler