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plugged in overnight or plugged in all
the time, so the car engine is always
warm. It can also be turned on with a
wireless switch module. Purchase a
light timer that can be set for Monday
through Friday; check the switch rating if it is big enough for your heater.
Also, a warm engine starts easier.
#3 I checked with my local car
accessories store; www.creativecar
audio.net. They have the system you
need. Not only is it programmable by
time, it can program by temperature.
[#6107 - June 2010]
RS-232 to Audio and Back
I have puppets which I can control
with a servo controller board attached
to the serial port of the computer. I
want to record the serial out to audio,
burn a CD, and then play the audio
from the CD and send the output to
the servo controller board, as though it
were coming from the serial port of the
computer. Anyone have an idea or
could help design a hardware solution
to this need?
I think I have a solution for you.
What I came up with is to use a
modem chip: the MX614. It can create
the sound signals that correspond to
the digital stream in and out of
the serial port, which can then be
recorded on a CD for playback to
control the puppets.
In order to verify it works, I
actually built the circuits and checked
it out. I was able to send a bunch of
ASCII data out the serial port, through
the circuit with the MX614, and into
another computer's audio in, capture
it, and then record it to a CD. I then
reversed the flow, so to speak, played
the CD, and fed the audio out back
into the circuit and then to the serial
port, and displayed the data on a
terminal window. The data was exactly the same as I had sent. I used
the terminal window program called
Etima Advantage Serial Port Terminal
program as the interface to/from the
serial port. It can send raw data you
type into a window, or send a whole
file. Any terminal program should
work. The MX614 chip expects digital
levels, so a MAX232 type chip was
used to interface the serial port with
RS-232 voltages (± 9-12 volts) values
to the 5V digital levels.
[#6108 - June 2010]
Noise Suppression in PIC Projects
We develop products with PIC
tech, but are unable to beat the noise.
Can anybody suggest a solution?
Use a ground plane, avoid radiating loops (watch for current return),
separate noisy parts
from sensitive parts,
pair), and shielding/
Use filtering on
ADC inputs to avoid
aliasing and noise.
bypassing. Slow Figure 1
down transitions if you can. Use oscillator dithering techniques if you can.
Use a resonating snubber to quiet
down switching supplies (application
note from Maxim). Fortunately, books
have been written about this subject.
Noise Reduction Techniques in
Electronic Systems, by Henry W. Ott is
the reference. Controlling Noise and
Radiation in Mixed-Signal and Digital
Systems, a web seminar by Nicholas
Gray from National Semiconductor is
another good resource. My personal
favorite is Linear Technology
Application Note 47, High Speed
Amplifier Techniques, by Jim Williams
(good explanations — probes, ground
plane, loop pick-up when measuring,
what to expect from scopes and
probes, what are the pitfalls; about 50
references). Microchip Technology
also has some good resources; look
for application notes by Bonnie Baker.
[#6109 - June 2010]
What is the least expensive system
to use to program a PIC16F876A? I got
one as a sample from Microchip; now
I don't know what to use to talk to it.
#1 I bought the PICIT2 programmer
from microchip.com and find it very
easy to use. I have very little
experience with programming PICs,
but with the PICIT2 I can load code
and burn it onto the chip. I have had