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Modulating data on a 12V power source.

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david90

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How do I modulate data signals on a 12V power source? What i'm trying to do is send data to a device with just 2 wire; gnd and vcc. The vcc line will power the device after filtering but it also will function as a data line.
 

banjo

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First you need to isolate the 12V power source and load with inductors. This keeps the rf modulating carrier from being loaded out by the filter caps.

On the transmitting end, you need to inject the rf after the series inductor right before it is sent to the load unit.

At the load side, you need to capture and decode the rf before the series inductor.

What frequency to use and the limitations really depend on what country you will be operating in. The long 12V power wires act like antennas and will tend to radiate your rf modulation signal. You can easily emit too much signal and find the regulatory agencies on your doorstep.
 

david90

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how do you inject rf??
 

banjo

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You inject and sample the RF through devices that would tend to block your DC voltage. Therefore, the usual device is capacitors.

Here is a quick example schematic:


The trace in the center is supposed to represent your +12V transmission line.
 

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