READER-TO-READER TECHFORUM
>>> QUESTIONS
Circuit Design Assistance
I am trying to design a voltage
monitoring circuit that will monitor a
12 VDC solar battery that is a little
larger than a car battery. The input
voltage signal range needs to be linear,
starting no lower than 3 VDC and up
to 15 VDC. The output signal needs to
be 4 to 20 mA ... 4 mA is 3 VDC and
20 mA is 15 VDC. On my schematic
(Figure 1), I would like to vary the voltage input at V1 and have the output at
R2, or something like that. I was not
able to figure out how to get the
circuit to produce my desired output
results without the use of a second
voltage source set to 4 VDC. If at all
possible, I prefer to have no power
sources other than the primary source
being monitored. Please help me
improve the circuit and solve this
extra unwanted powering problem.
Also, recommend any alternative
components that have lower power
requirements.
#12101
James McAndrew
Lafayette, LA
Garage Door Remote Control
My garage door opener remote
operates using a carrier frequency
designated W, with modulating frequency 52. Since it is now inoperative
(with a fresh nine volt battery), how
may I begin to repair or replace
either the transmitter or receiver? The
manual control connected to the
receiver works fine.
I've done a fair amount of
electronic circuit design and repair,
but nothing in this frequency range
which I believe is up in the MHz
range. I'd like to not have to replace
the entire door opener.
#12102 P. Kaltenborn
Fair Haven, NJ
EHT with an
op-amp or the
components
around either
a CA3140 op-amp or a
LM358 to
change the
output Z of an
EHT stick. I
want to use it
with other test
equipment —
like a frequency counter or
oscilloscope — to make sure I have a
sine output of a flyback from an
amp that I’m working on. Or, other
suggestions to change the Z output.
2) Where can I find out the value of
a fuse for the CONAR Model 251
oscilloscope and/or where can I get a
manual or schematic for this scope?
(CONAR was bought out by the
National Radio Institute - McGraw Hill
Continued Education which is no
longer in business.) I want to power up
this scope and test its output. I need to
know the fuse type and amps before I
test it, as money is in short supply.
Or, is there a website to find this
information?
#12103
Figure 1
James New
Jacksonville, FL
Clickers and Clackers
What are the most appropriate,
readily-available, low-cost, low-power,
and reliable radio transmitters,
receivers, microcontrollers, and USB
modules or chips for building clickers
and clackers defined as follows?
A clicker is a handheld box with
eight buttons and one of 32 codes.
The box contains a microprocessor, a
radio transmitter, and an easily
replaceable battery power supply.
When a button is pressed, the clicker
radio transmitter emits one byte of
data, identifying the button with three
bits and the clicker with five bits.
Transmitter range needs to be no
more than 200 feet.
A clacker is a device in a small box
containing a radio receiver and a
microprocessor that is powered by
and corresponds via USB with an
application program running under
Windows XP (or later Microsoft OS).
The application program user
interface includes a start button and a
stop button. The program maintains in
RAM a 32 row by eight column bit
array and is normally in an idle loop
waiting for the start button to be
pressed. When the start button is
pressed, the array is set to all 0s and
the program enters a loop, ready to
receive data bytes from up to 32
clickers. If a byte arrives, then a 1 is
entered in the correct row and column
of the clicker code and clicker button.
When the stop button of the user
76 December 2010
EHT With An Op-Amp
CONAR 251 Scope Info
1) I need to know how to use an
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