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INTRODUCTION
In today's world there are many situations that require monitoring, but no one
can be in four places at once. Now, with the AVS10, you have the opportunity
to see four different locations and keep an eye on your precious property.
The front doorbell is ringing, the baby is napping, one of your children is
playing with friends on the backyard trampoline and another is shooting
hoops in the driveway. Of course, you need to be in the kitchen or home
office and even with the proverbial parental "eyes in the back of your head"
you can't possibly keep an eye on everyone! With the AVS10 and four
inexpensive video cameras you can do the impossible. And if you see a
situation that requires a longer look, simply press the SCAN/STOP button
and take as long as you need to assure you that all is well. The AVS10 is the
perfect baby/playroom monitor, allowing you the freedom to monitor the
action without having to be physically present. You can keep an eye on your
shed, boat or other outdoor property as well. We believe you'll find dozens of
applications for this useful kit and at a fraction of the cost of commercial
video switchers!
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CIRCUIT DESCRIPTION
The AVS10 takes advantage of the Motorola 68HC908 family's power, thus
eliminating the need for bulky logic gates to control the switching of up to 4
input video signals. By periodically testing the state of each enable switch
(S1:1 – S1:4), the microcontroller (U1) will activate the respective video
control switch (U2:A – D) enabling each individual video feed.
The 68HRC908JK1 microcontroller uses an RC (Resistor & Capacitor)
network to set up the controlling frequency. Resistors R1, R2 (variable front
panel potentiometer), and R3 along with the fixed value capacitor C1 make
up the timing circuit for the system. The front panel speed control (R2,
variable potentiometer) lets us vary the control frequency from about 2MHz to
8MHz. This is how the scan rate between the input video signals is controlled
giving the user full range from approximately 1 to 5 second switching times.
The SCAN/STOP button (S3) lets the user stop on any active video channel
and hold that particular feed for indefinite viewing. The active low enabling of
the IRQ line (U1 pin 1) from S3, the SCAN/STOP button, gives easy access
to the end user for other remote scan stop triggering in custom applications.
Using the CD4066 Bilateral Switch (U2) as the actual video control switcher
lends itself nicely to this application. The quad bilateral switch was intended
for the transmission or multiplexing of analog or digital signals with a switch
"ON" frequency response of up to 40 MHz! This is really overkill for a video
switch unit but it offers great performance and extremely low switch leakage
between the video channels when powered.
AVS10 – 4
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