QUESTIONS & ANSWERS
You should be able to make a
single-sided layout by using jumper
wires where crossovers are needed.
QI have a collection of about 25 different video game systems. I have them all set up and ready to play but I
have to “cable swap” every time I
want to play a different system. I
have a couple of four and six input
switchers, but that gets complicated.
The cables are composite A/V (red,
white, yellow, and stereo audio).
What I need is one circuit that can
handle all 25 systems. What I would
like is one pushbutton next to each
When you push the button, it
will disconnect any other system that
was selected and instead connect the
system that is selected. Maybe an
LED next to the selected system
could be lighted. I have tried relays
(my usual method) and PIC chips,
but I am unable to figure out how to
switch the sheer number of inputs
that I need. Perhaps you can help.
— Derek Tombrello
■ FIGURE 3.
ATwenty-five systems times five cables equals 125 signals to be switched to five outputs. My solution
(Figure 3) uses a flip-flop which when
set, enables five solid-state relays to
feed signals to an audio/video bus.
Flip-flops in the other 124 channels
are reset, but the selected is not reset
because C1 delays the set signal to
insure that the flip-flop ends up in the
set state. Figure 3 shows one
channel which is to be repeated 25
I did a preliminary layout to see
how big the circuit board would be; I
estimate that if half the ports are
flipped to the other side of the bus,
the board would be three feet by 6-
1/2 inches. The board length could
be reduced by using three vertical
video jacks and two vertical audio
jacks, but I did not find any in stock
anywhere. Figure 4 is the Parts List.
QOver the years, I have found that the Q & A section of Nuts & Volts has always come to my rescue
when I needed a circuit to solve a
problem. At this time, I need a simple
PARTS LIST FOR VIDEO SWITCH
■ FIGURE 4.
RCA JACK, THRU HOLE
SS RELAY, 2 OHMS, 60V
8 RESISTOR ARRAY,
270 OHMS 652-CAT16-271J4LF MOUSER
270 OHMS, 1%, 1/8W, 1206 660-RK73H2BTTD2740F MOUSER
10K, 1%, 1/8W, 1206 660-RK73H2BTTD1002F MOUSER
SINGLE D FF 863-NL17SZ74USG MOUSER
0805, SMD, GREEN 604-APT2012SGC MOUSER
July 2012 25