I don't think you mentioned number of units that need to be addressed.
May makes some difference to addressing etc.
Assume say 16 max - can be more if needed.

I don't think you mentioned the on/off rate.
Assume slowish.
Say 1 Hz or less per lamp.

I don't think you mentioned wattage per lamp or power feed voltage, which
affects holdup capacitor size. From 1st principles, a capacitor will drop a=
t
1 Volt per micro-Farad per milli-Ampere per milli-second. Rearrange that as
desired.

Bidirectional data makes it a little harder, but:

- Almost any modern processor with an RC clock will do what you want. Numbe=
r
of I/O will be your main limit. For "normal async" coms you want a high
accuracy clock for worst case sync. Hi accuracy PIC RC versions are good
enough. Price of a resonator is low enough as to be a good idea if you want
an easy life.
Other than standard async coms can be used to allow clock recovery.

Why do you need bidirectional?
ie what will you do if it doesn't work, apart from damage control?
Bidirectional isn't hard but unidirectional outgoing is easier.

If you use a data rate that is short per frame  compared to eye/brain
response you can modulate the bus at power levels with data. This will lowe=
r
the mean DC level. By spacing data bursts N frames apart the DC drop is
reduced. eg if the average data word contains equal numbers of high and low
bits then  the DC level drops by a factor of (1-1/2N) if there are N frame
times in which only 1 frame has data in it. (Eye probably doesn't perceive
flicker at 1/100th of a second break - maybe longer. Discussion always
ensues on this.) .

If you have some DC bus "headroom" above what the LEDs need you can modulat=
e
just this part of the DC level and so drive the LEDs with less impact, or
none.
eg 5V bus, 3V LEDS say. 2V headroom must allow for local regulator and
wiring etc drop but an eg 0.5 volt data signal will probably never cause
regulator drop out.

You can use tone signalling ()modulation) on the power line as long as you
have blocking filters at each slave.

If the distance is reasonably short then a 3 or even 4 wire bus will make
life much easier,

Russell
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