occurs at the B input before the
counter times out, the start-stop
flip-flop is reset and the counter
stops until another pulse occurs
at the A input. If the B pulse does
not happen and the timer times
out, the alarm flip-flop is set, the
timer stops, and stays in that
condition until manually reset or
another A input pulse occurs.
VCC can be between five and 15
QI am looking for
a schematic for a
transmitter and receiver
that can be integrated into
my home entertainment system. I have
5.1 surround and would like to find
some way of sending the separate
signals for each channel without
the use of speaker wire. The transmitter can run off 110 VAC and the
receivers can be battery operated.
XMTR: RAMSEY FM10C
RCVR: RADIO SHACK 55012487
RCVR: RAMSEY FR1C
PWR AMP: RAMSEY UAM2
Any ideas would be appreciated.
— Robert Burleigh
AMy solution is straightforward
but has lots of parts (see
Figure 2). You can build the
units from kits or buy ready-made units. The FM transmitter will be
■ FIGURE 2
L-C tuned — not crystal controlled —
unless you go for an expensive setup.
The receiver also has to be L-C tuned,
not frequency synthesized because the
transmitter will drift in frequency.
The L-C tuned receiver will have AFC
(automatic frequency control) and be
able to track the drifting transmitter.
Here is an alternative for your
R/C Eliminator schematic, Figure 6
on page 27 of the August ‘07 Nuts
& Volts. This should eliminate
both the high speed pulses and
the gap in pulses you mentioned
with the two switch types. I have
reproduced only the right half of
that figure and simplified the
capacitor arrangement in Figure 3.
— Edwin Hampton
and has a power bandwidth of
60 kHz. The older five pin device
was no doubt compensated for a
gain of 10. Anyone planning to
use it for high frequency should
insure that they are getting the
five pin device.
Response: Thanks for
the feedback, that is one to
max, 10 amp max and unity gain
at 3 MHz. I forget if the LM12 is
unity gain stabilized, but I usually
feed them back at X10 gain and
set a signal divider on the input
to give the desired output swing.
They come in a five pin TO- 3 case
and there used to be sockets
available for them. I usually
use a Texas size heatsink
designed for a three pin
TO- 3. I think Jameco (www.
jameco.com) sells the insulat-
ing mica for them; I use this
as a template to drill the other
three holes in the heatsink.
Two of the pins match the
normal TO- 3 pattern.
A source that I use for up to
60 watts at 1.5 MHz is the LM12.
National made this power
op-amp about 20 years ago and
there are still tens of thousands in
supply, so I think they qualify
as hobby material. I seem to
remember the spec as 60 Vpp
Response: I looked up
the LM12 and found that
Digi-Key has it in stock
for $42 each. The version
available now has four pins
(case is V-) and has a small
signal band width of 700
kHz. It will output 10 amps
October 2007 25