Hello.

In a part of a project i am asked to work on, we need to transfer some data (very simple 0/1 informations) via the power lines of a car's battery.

I've made a lot of googling on the net, and i see that it is doable, but can't find and example circuits..

I guess that picking up the information will be done through some kind of high pass filter and tone decoding (or similar approach)

However i have no clue on how to "inject" the data into the power lines..?

I found this ready circuit, but i don't think it is cheap enough for out application:
DCB500 SPI/UART power-line communication modem transceiver for automotive network

Does anyone here know of some cheap transceiver that can do the job?

any info on the subject is welcome.

thanks a lot.

 

Have a look at this:

http://www.freescale.com/files/share...ide/SG2042.pdf

Looks like they use inductive coupling (i.e. a transformer).

Shouldn't you also be able to use capacitive coupling?

 

Thanks.. do you think i can attempt to do it my self with caps, op-amps and a micro controller?

do the way of injecting the data via magnetic waves is applicable for DC lines?

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

The difficulty with using capacitive coupling is the low impedance of the line. A transformer allows for impedance matching between the driver and the line to generate a larger signal in the line.

This technique can be used to inject a signal into either AC or DC lines.

__________________
Carl

 

How can i connect a transformer to DC lines? it'll make a short circuit...? or should i isolate the transformer from the power lines with a capacitor?

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

Yes, you can block the DC with a capacitor.

__________________
Carl

 

Is this how it may be done?

i draw that circuit, please tell me if my approach is correct..

Am i missing some important components like diodes or transistors somewhere... (seems like a stupid and ugly question, i know! )

Also, i included two versions.. can you tell me which one is better and why..?

and at last, would that work at all?

thanks a lot

Attached Images

tranceiver.jpg (68.7 KB, 41 views)

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

This idea is fraught with problems due to the noisy nature of the automotive environment. The noise from the alternator and fuel injection systems is horrible. What is wrong with an extra wire? Now if all you are trying to do is have a master device and a slave device and can power the slave from the master with nothing on the power buss between them, then there is a fairly simple way of doing this. Otherwise, the Yanmar product or similar is the way to go since all the complexities are figured out for you.

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Well i can give it a try and see with a scope how to signals look like.. but can anybody answer my previous post..? thx

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

hi ika,
Basically both your circuits are capacitance coupled to the power line.

The power lines are very low impedance and require a low impdance driver, that is, inductive coupling using a transformer.

What frequency are you going to use.?

EDIT:
If you do consider using an 'extra' wire, look at a short fibre optic link from the sensor to main unit.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

There are going to be many sensors, so, power line carrier are ideal.. (from an economic point of view)

I am going to use a high frequency.. i guess something in the 500 KHz range..

Don't you think i should use op-amp based high pass filter instead of simple capacitors?

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

hi,
I would think that 500KHz is a little high, around 100KHz would be my choice.
A range of prewound transformers [ for mains injection] are available, why not choose a suitable freq transformer.

I would use active filters OPA etc rather than just passive RC filters.
The lines are going to be VERY noisy and would expect some tight filters will be required.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

aren't there some ICs that handle this task of communicating over DC power lines?

i would be astonished it there wasent.. but i can't seem to find it on the net.. maybe i'm not looking the right place

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

 

Have you tried Googline "Bias T" circuits? THe data is sent as an AC signal superimposed on the voltage of the DC power line and is AC filtered at the receiving end. A capacitor sits between transmitter and the power line to superimpose the AC data signal onto the DC power, and a capacitor sits between the power line and receiver so the DC gets filtered out and the receiver only sees the AC signal.

 

Thanks.. quite interresting.. (i don't know what happened to google those days, each time you search for something, you get the first 2 pages full of Patents that nobody care about!)

anyway, i found this circuit, can someone help me to modify it to make it work on a car battery instead of AC?
Digital Remote Thermometer

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/