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Most schemes use either a shift register or a decoded up/down counter.
The
best solution these days is a PIC chip because you can use just a couple
of
chips and make multiple patterns- the "ping pong" sweep, the slow "from
either
end to the middle" idle mode, etc.
Another simple solution uses a bar graph chip in dot mode and a
triangle
wave generator- one LM3914 and a dual op amp for that solution.
A four bit binary counter and a decoder can also do it- the CD4028
chip is
made for this task. Use a CD4029 counter, CD4028 decoder, a CMOS 555 as
the
clock source, and a CD4013 flip flop to keep track of the up/down status.
You
will drive the lamps from the 0 through 7 outputs of the 4028 and you will
toggle the flip flop from the 0 and 7 outputs- this makes the counter
reverse
direction when it reaches the limit.
Now, are you using incandescent or LED lamps? If you use incandescent
lamps, you can use just about any power transistor to drive them. 2N3055s
or
TIP127s are fine, and in fact you can experiment with whatever you have in
the
junk drawer.
But, if you use LEDs, you will want to make a "fader" circuit to make
the
LEDs lose intensity over time. You can drive them with a FET and have a
capacitor/resistor on the gate lead to do this, for a simple solution.
But
there are many, many ways to build this circuit.
If you opt for the PIC chip, you get the advantages of only one chip
to do
it, plus your drivers. And you get multiple pattern options and the
ability to
fade LEDs with PWM...
Cheers!
Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
Thanks man- I'll let you know how I get on. ---------------~{X}~--