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Injecting a communication signal over DC power supply lines

I have a pretty simple circuit, but I need to send an output PWM signal through the same place I'm getting my voltage. The voltage is DC, so I figure since my PWM is an AC current, I can use a low pass filter to send the signal through, while getting DC current from the supply. I'd prefer to use a capacitor/resistor filter rather than an inductor, but I'm unsure how I would go about creating one for this particular circuit. My problem right now is that the AC signal goes back to VCC rather than to my AC Input (that also supplies my power).

enter image description here

For an inductor, I'm guessing I'd put it on the path to VCC of my microcontroller? Where would I do it with a capacitor?

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    \$\begingroup\$ Can you re-write your question or post a schematic? I dont understand the problem. "I need to send an output PWM signal through the sae place I'm getting my volage" huh? \$\endgroup\$ – Michael Jul 6 '12 at 2:43
  • \$\begingroup\$ The imgur link has a schematic. I'm sending an AC signal up a power supply that I'm receiving a DC supply from. \$\endgroup\$ – Connor Jul 6 '12 at 3:05

It would appear that you need to put a series capacitor at the wire labeled AC PWM to block the DC power supply voltage from reaching the PWM pin on the MCV. The size of the capacitor is determined by the frequency spectrum of your PWM signal since any size capacitor will block the DC. You will also need an inductor at your power supply. The inductor will allow the DC current to reach your circuit but will prevent the PWM signal from being shorted by the low impedance of your DC power supply. The size of the inductor is determined again by the frequency spectrum of your PWM signal. Its current carrying capacity, however, is determined by how much DC current your circuit is drawing. You can recover your PCM signal at the load side of the inductor.

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