Power line networking

Lee Marshall

how is it supposed to work?
the way i see it, your going to have to fluctuate the voltage of the power line, in order to transmit a signal.
how is that achieved?
I want to try interfacing a microcontroller(the prop) to a car's LIN network.
What actually goes on inside those LIN transceivers which allows a signal to be transmitted across a power line without messing up every device powered by it?

I have been curious about this for some time, especially with all the ethernet-over-powerline stuff.

lee

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I hear and I forget. I see and I remember. I do and I understand
-Confucius

Post Edited (Lee Marshall) : 11/7/2007 7:20:27 AM GMT

uxorious

Power line networking works off the same principle as DSL on a phone line. Higher frequencies are used to transmit data riding on the 50/60hz power source. Because the frequency is much higher, the voltage fluctuation is negligible. However, the amount of interference from the signal is it's major downfall even though speeds of 1-3 mbps are typical with common house wiring. Noise generated by broadband power line networks (BPL) is a rather hot topic in the US, especially among the amateur radio community and that is why you don't see it as a solution anytime soon. Just do a search for "broadband power line" and focus in on European based results. You will find tons of info. I spend more time on the opposite phrase "power over ethernet". I am working on some POE projects right now.

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~~ dRu ~~

Lee Marshall

thanks for the info, much appreciated.
however, i am more interested in DC powerline networking(like in cars).
the thing that really got me, is trying to understand what kind of device you would need to actually alter the voltage(to transmit the signal) on a power line.

BATTERY(12v)
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······· |(Power line)
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LIN Tranceiver·

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MicroController·

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Temperature Sensor
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LIN Tranceiver·

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MicroController·

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Oil Sensor
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······· |

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······· |··········································································· |
LIN Tranceiver·

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MicroController·

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Sunroof Actuator
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·HeadLights

how does the LIN Tranciever actually drop/raise the voltage?

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I hear and I forget. I see and I remember. I do and I understand
-Confucius

Post Edited (Lee Marshall) : 11/7/2007 2:10:55 PM GMT

uxorious

Lee, sorry, I totally missed the LIN point of your question. LIN is a little different and rather sophisticated. The spec is a tough read, but details the workings. I believe the power line for the LIN network is not directly connected to the battery. It passes through some circuitry in the main control unit to create a vBus that is X volts lower than your supply voltage from the battery. That gives you a way to adjust the voltage for the data transfer. So maybe you have 12 volts at the battery and 11 volts comes out of the control unit to supply all the LIN network devices (probably would be a voltage equal to vBat minus a voltage drop across a diode or something). The LIN network may use "data" that consists of "lows" at say 10 volts and "highs" as 11 volts. It's a little more complicated than that but that's the fundamentals I know.

Go to the link below and you will receive a link to download the spec in an email in about 5 minutes. I would post mine, but the PDF is generated by the online request which has a border that says who it is registered to and mine's for my work. Section 6.5 on page 114 starts the DC/signal parameters.
www.lin-subbus.org/index.php?pid=8&lang=en

Yamar is a partner of Daimler Chrysler that makes chips for LIN products and has a cool animated gif on their home page for a LIN example. www.yamar.com/index.html

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uxorious

Just stumbled across this tonight, new at digikey:

Cypress PSoC LIN Eval Kit, p/n 428-1926-ND

search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=428-1584-ND

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~~ dRu ~~