E
45), which connects to a PC via the composite video-to-USB adapter. Using the camera
cable wiring (Figure C), you can easily shorten
the cables for cameras installed closer to the
switcher. You can also lengthen a cable, but
the video quality may suffer.
camera is given, reading the setting from a
potentiometer. Four LEDs provide additional
visual indication of which cameras are on.
Figure D shows the schematic for the
Picaxe-14M switcher; you can see it full-sized, along with the PIC16F684 version,
at makeprojects.com/v/30. The 4 camera
inputs run to switcher input pins 1, 11, 8, and
4, and microcontroller output pins 2–5 (IC
pins 8–11) determine which one routes to
the shared video out. On the input side of the
controller, input pins 0– 5 (IC pins 3–7) read
from the toggles and potentiometer.
F
moisture. I sealed the connector inside a
plastic bag and have had no problems since.
To build the switcher, first solder the
onboard components as marked on the PCB,
with 14-pin sockets in place for the switcher
and microcontroller chips. I connected the
LEDs sticking up on their untrimmed leads,
to poke through the enclosure with the board
mounted upside down, but you can also connect them offboard with wire, as MAKE Labs
did in Figure B. You can use a small onboard
potentiometer as shown here (Figure E), or a
longer one for making adjustments without
opening the enclosure.
The camera video cables will plug into a
homemade video switcher (Figure B, page
David Bodnar
For the offboard connections, solder the
center leads from the RCA jacks, which will
carry the camera signals, to pads In1–In4 on
the board. Solder one side of the toggles or
DIP switches to Sw1–Sw4 on the board. For
ground, run wires connecting the outer contacts of the RCA jacks and the unconnected
legs of the switches (Figure F). Don’t connect
the DC power jack or video out cable yet.
Drill holes in the project box for the PCB
mounting screws, LEDs, switches, RCA jacks,
power jack, and video out cable, marking
positions for proper PCB alignment. Cut the
RCA cable, thread the cut end through a hole
drilled in the enclosure, tie a knot for strain
relief, and solder it to Video Out on the board,
center contact to (+) and outer shield wire
to (–). Mount everything. I mounted the PCB
and controls inside the lid (Figure G, following page). If you’re using DIP switches, which
aren’t designed for panel mounting, you can
thread the wires through small holes and glue
the switches to the outside. The completed
2. BUILD THE VIDEO SWITCHER
A video switcher takes inputs from multiple
cameras and cycles through them at a user-settable interval (between 1 to about 30
seconds), routing each of them in turn to its
single video out. It’s not a complex device,
and it contains just 2 chips: a 4066 quad analog switch and a Picaxe-14M or a PIC16F684
microcontroller (either one works). The 4066
routes the video inputs to the single output.
Meanwhile, the microcontroller controls
which cameras are active, reading from 4 toggle switches, and times the interval that each
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