Connect regulated +5V DC supply for operation of board. Outputs Q1-4 and VT are active high output at 5V level. If any LED is on, it means that output is at high level. VT LED blinks once a new DTMF tone is received. The binary data appears at Q1 to Q4. Input signal can be from an audio source like microphone amplifier, FM radio receiver, wired phone line. Please note when connecting land line phone signal, do not connect ground wire of board to phone line directly. Use a 100nF capacitor in series to phone line wires at ground.