Data and power over 2 lines

[ecoli-557]

Greetings to All-
I have searched some of this site (would take a month to do it all!) with various keywords and have not gotten the inspiration needed <grin>.
I would like feedback on what others may consider as the best way to commumicate between several PICs over the DC (could be AC) wires. I would like to only use a single pair for both data and power.
I was thinking about 1 wire commands between the PICs but any serial protocol could do such as SNAP.
No real restriction the voltage as I would plan on regulators so the DC could be AC and as high as 24 VDC (or AC).
The lengths of wires could be as long as 500 feet or as short as 100.
Curious if anyone else has attempted this?
Regards!

[mackrackit]

Here are a couple of threads, nothing but ideas though.
http://www.picbasic.co.uk/forum/showthread.php?t=9406&highlight=design
http://www.picbasic.co.uk/forum/showthread.php?t=9559

[ecoli-557]

Dave-
The second is similar to what I am thinking of, I have also just considered capacitively coupling DC squarewave output from the USART onto the DC lines, but that seems too simple.
Am I making this harder than it needs to be?
-Steve

[mackrackit]

I think the answer is in the first link, post 29 and 31. But I have not tried it.
Being that you want to use the lines to power the PICs, have a filter at each PIC and send / receive the modulation between the filters.

But I am having one of those days where every LED I pick up is backwards. So just ideas.

[ecoli-557]

I just turned up this interesting ref on something that may work.
http://www.interfacebus.com/Design_Connector_MI_Bus.html
I could use this as an interface between PICs and use PICBASIC PRO and use 1-wire or some other protocol?
Anyone have any thoughts?

[Archangel]

I just turned up this interesting ref on something that may work.
http://www.interfacebus.com/Design_Connector_MI_Bus.html
I could use this as an interface between PICs and use PICBASIC PRO and use 1-wire or some other protocol?
Anyone have any thoughts?This was commonly done, before cable/satalite TV, people used to put preamplifiers on the antenna mast, and power it from a wall wart on the ground using only the coax / twin lead cables. Remember chokes pass DC and block AC, Capacitors pass AC and block DC.

[aratti]

Intersil has several dc and ac transceiver which will surely solve your problem!

[boroko]

Have been working on the same issue:
http://www.picbasic.co.uk/forum/showthread.php?t=9559 might get you started.
I am part way through getting it to work using DT's Int scheme.

The system uses reversing DC on the wires to send data. The length of the reversal is correlated to the data.

I am using the DCC spec as a learning tool, but my uses are different, so I'm changing it a bit. I'm also using auto-detect for polarity into the USART. It is going to require a part that has a selectable comm polarity. A couple of examples are 18F2420 and 18F2525. Look at BAUDCON.4 (TXCKP) and BAUDCON.5 (RXDTP).
Cool once I found out about it.

I am hoping that I can post the results here, but so far, still banging my head like Mister-e's icon!

Bo

[ecoli-557]

Bo-
The app I am trying to work with is sending data over the phone lines when no call is active. Like you, my app does not really need to interface to anything over than whatever I come up with.
I need to have bi-directional data go back and forth so I was working with superimposing AC over the DC on the phone line.
I have not gotten very far with this yet.

I would be interested in how you do to see if it may answer my problems.

[dhouston]

Before using the phone lines you need to do a bit of research. In most jurisdictions it's illegal to do as you propose. In the USA, you need to comply with FCC Part 68 rules.

[ecoli-557]

Sorry-
I am not working with the Ma Bell lines, just the lines after the phone switch. I need to get data to and retrieve data from an analog phone. Right now all I have is the pair of wires. If I can use the power from a non-inuse phone line and modulate the 48 VDC (which I am generating) I should be able to get data to and from the phone. The data will go to and from a PIC which will carry info about numbers called, time of day, etc.

My fall back plan is to use another pair, feed DC to power everything and still modulate the DC. The second pair approach is much easier for me but much harder for a retro-fit.

I am not folling with Miss Bells lines, otherwise I would be working from jail....... and getting a soldering iron would be tough <grin>.