Data over Power lines.... Sort of.

I have this string of DC yard lights out front and I want to use some Arduino stuff to control them individually. My problem is that for various reasons I can't touch the DC line that feeds them.

So I have two wires carrying around 24v DC to work with and that's it.

I know wireless is the obvious solution, but I'm not interested in that right now. (And I, I chose the the road less traveled by)...

My question is, is there any easy way to modulate, say, a 2400bps onto that line short of gutting like 10 ancient modems?

Going for small and compact here.

I think you can get gizmos to do ethernet via wall outlets which might work in your setup.

is there any easy way to modulate, say, a 2400bps onto that line short of gutting like 10 ancient modems?

Not sure why you want to gut 10 modems, but the modem chips are still available. Alternatively you can do it yourself with an FSK modulator / demodulator chip. (FSK = Frequency shift keying)

I think you can get gizmos to do ethernet via wall outlets which might work in your setup.

I have some (used for their original purpose) and they work well but they aren't cheap and as this is not 230/110V, they would probably need quite a bit of modification. And you'd need two ethernet shields...

Mowcius

How much data do you want to transfer? if it's only something simple perhaps you could come up with something more rudimentary.

Yes… More rudimentary… I figured some sort of serial driver, maybe for RS485 would be good, I just don’t know how to strip the signal out of the voltage.

Have you looked into those cheap 433MHz radios? You might even be able to couple the RF to your DC cable if transmission through the air doesn't work out.

I figured some sort of serial driver, maybe for RS485 would be good,

No not really that requires a DC response, what you need is an AC modulation that you cnd tap off the power rails with capacitors.

I'm trying really hard to learn here... How exactly can capacitors "tap" a signal off the power rails??

How exactly can capacitors "tap" a signal off the power rails?

You connect one end of a capacitor to a power rail and the other end of the capacitor to the modulated signal. You do the same at the other end into the demodulator. That's how data transmission over power lines works.

If the power line is DC then the capacitor blocks all the power from getting into your modulator or demodulator. If the power is AC then you choose a modulation frequency sufficiently high and suitably low value of capacitor that the modulated signal pisses straight through (technical term) and naff all of the power can get back.

That’s awesome! Thanks!

I’ll mess around with that some.

Ok... Capacitors do indeed seem to block DC, but only after a while.

How do I deal with the power coming across while the capacitor is charging??