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How to Isolate an Analog DC Signal

Analog electronic circuits carry two basic types of electrical signals: direct current (DC) and alternating current (AC). DC flows in one direction from a positive terminal, through a circuit, to a negative terminal. AC flows back and forth through a circuit, usually at a steady frequency. AC and DC are sometimes mixed, and you may need to isolate a DC signal from AC. You can accomplish this with a simple resistor-capacitor low-pass filter. The low-pass filter allows DC through and removes AC. The higher the frequency, the more the filter rejects the AC signal.

Things You'll Need

Solderless breadboard
10,000-microfarad, 35-volt capacitor
10K-ohm 1/4-watt resistor
2 pieces of red 22-gauge wire
2 pieces of black 22-gauge wire

Instructions

- 1
  Insert the capacitor's leads into adjacent columns on the breadboard. Holes sharing a single column in the breadboard are internally connected to each other, but adjacent columns are not. You make electrical connections to components by inserting wires so they share the correct columns on the board.
- 2
  Insert one of the resistor's leads so it connects to the capacitor's positive lead. Insert the end of a red wire so it connects to the same capacitor lead. Set the other resistor lead into an unused column in the board. Insert the end of the other red wire so it connects to the second resistor lead.
- 3
  Set one end of both black wires into the board so they connect to the capacitor's negative lead.
- 4
  Connect the first red wire to the positive terminal of a source of mixed AC and DC signals. Connect a black wire to the source's negative terminal or ground.
- 5
  Connect the second red wire to the positive terminal of a circuit to which you wish to provide a DC signal. Connect the remaining black wire to the circuit's negative terminal or ground.

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