You eliminate the power transformers (T1 in each) and and rectifier diodes (D2, D3 and D3, D4) and connect the regulators (IC3 in each) to the battery (through a small resistor and 15V zener to ground to suppress transients).

IC3 in the reciever is a 78L12, 12V regulator, which requires a minimum of 14.5V to work. This regulator will need to be replaced with a 12V low dropout regulator. Alternately the circuit could probably be modified to work with a lower voltage regulator such as a 78L09, 9V device.

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Carl

 

hi Carl,
I think what ika is asking is, how to modify the circuit to enable data transmission via the vehicle wiring
rather than the local mains supply.?

Regards

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Eric
"Good enough is Perfect"

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Sorry if I wasn't clear. My comments were how to modify it to be powered by the battery which I thought was the main concern.

The signal transformers L1, shown connected to the AC, instead would be connected to 12V power through the cap and to ground (the ground side doesn't need a cap). I assumed that was sort of obvious but I guess it is not.

This scheme may not work as well in a car as with a power line since a power line has balanced wires for the signal and return path. The car has one wire and a chassis return which may muck of the signal some. Only way to know is to try it.

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Carl

 

hi,
If it was my project, I would get a car battery on the bench, make up that matching transformer/drive and drive it with a signal generator.

See at which frequencies, if any, the battery offers the highest impedance to the 'ac' test signal.
I think the problem on a car is all that electrical noise from the different systems.

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Eric
"Good enough is Perfect"

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Bill's: www.blueroomelectronics.com/

 

I really hate that too and it seems that Google Domain filter won't remove them from the list either. Someone is being paid.
The reason these work well on the 50/60Hz AC line is that the impedance of the power line is relatively high at higher frequencies so it is fairly easy to superimpose a carrier on the AC line.
Compare this to the 12V DC bus of a car where most of the electronics have a capacitor across the DC input which presents a low impedance path to ground for any carrier you try to superimpose.
As I alluded to, and dknguyen stated, the best way is something like this:

Attached Images

Data-Power.PNG (12.6 KB, 17 views)

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Thanks a lot for taking the time...

can you tell me what are those triangles in your schematic? are those buffers...? i don't quite understand the part where 12VDC is mixed with data.. Also shoudnt we use a High pass filter instead of the LPF?

thx again.

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

 

The filters on the electronics inputs certainly could be a problem. You may need to add an inductive choke in series with each electronic input to maintain the signal.

But I don't understand how the circuit you propose will get around this problem since it's outputing a signal at some frequency, which will also be suppressed by the caps.

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Carl

 

The first triangle is just a powerful buffer. When idle, it outputs 12V. When sending data, the output swings between 12V and ground. The diode and cap on the input to the regulator peak detects this signal and supplies a relative steady 12V to the regulator. The data rate will be fairly slow, hence the lowpass filter. The receiving buffer is just a simple schmitt type.
If you wanted to make this data path bidirectional, the circuitry would be somewhat different.
What I'm proposing is running one wire between the master device and the sensor/slave device. No regular devices (Car radio, ECU, lights, etc) are on this data/power wire. I really don't see the point in trying to run power/data on the existing stock car wiring as it seldom goes where you need it and seldom has the extra capacity or state (Batt, Ign or Accy switched).

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Thanks a lot for your insight... i think i'll give it a try. at least to learn!

Can i ask you one more favor: Where does the battery's 12V wire goes in your circuit? Can you pin point the node that is to be connected to the 12V line?

thanks a lot.

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

 

Hello again..

I want/need to make some tests, and see with the scope how a car electrical system responds. I just dont have a clue on "how to inject data into DC" i understand the principle, but i can't figure out how to make that work with the components that i know : coil, cap, BJT, resistor, etc...?

can anyone give me hand on that?

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

 

If there was a simple / cheap effective solution to send data through a vehicles 12V DC wiring then why would cars still use CAN bus?

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Smart Kits build Smart People
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It is the power pin for the first buffer. In the upper left hand corner where it says "Power In 12V". Basically all power flows though the "buffer" placed on the left hand side of the diagram.
Well, you could always modulate the field coil of the alternator!
Basically, you would use chokes/inductors to separate the signal from the rest of the system and capacitors to couple into this "isolated" piece of line. The trick is to use chokes that can handle the DC current without saturating:

Attached Images

PwrSig.PNG (3.7 KB, 5 views)

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Seek out the datasheet for the Maxim IC 455, the application notes pdf has a complete circuit diagram. The chip is just a video amplifier and switching, but the application notes show how to send and recieve both DC power and control signals over a "single" wire.

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Are you trying to re-invent the ancient BSR X-10 modules?
Transmitting AC signals onto a noisy automotive DC power line is futile. The separate wire is the best approach. Wireless could also be tried, it is unaffected by high frequencies under the hood.

 

If the wheel had not been re-invented then they would still be made of wood!

As for the 'futility' of getting data over a noisy DC line the problems are not beyond a solution, indeed if anything many real world examples of 'fly-by-wire' can be found not only in aviation but automotive applications.

Closer to home some manufactures of traffic control systems, both temporary systems used during road works and permanent installations communicate both sensor and control data over the DC power line. If you think an automotive DC power line is a bit 'Rough' the you should see what the output of a beat up generator looks like

Sticking with in-car applications a quick search of the web reveals a nifty idea to use the DC power line to inter-connect the various elements of 'ICE' (In Car Entertainment) no rolls of wire for the speakers or getting under the dashboard to run the control head cable back to the CD changer in the trunk. Just put the hardware where you want it and find a live wire.

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It may seem like a good idea at the time , but never stir your cold coffee with a soldering iron.