circuit harness wiring

The two T-notch filter can be used to block unwanted frequencies or if placed in an op amp as a bandpass filter. the notch frequency occurs where the capacitive reactance equals the resistance (Xc = R) and if the values are close, the attenuation can be very high and the notch frequency virtually eliminated,Insertion of the filter depends on the load, the output is connected to the subject so that the resistors must be of much lower value than the load for minimal loss.

Twin-T RC Notch Filter Circuit diagram
For audio frequencies, the filter may act as a bass and treble boost circuit by attenuating the midrange. With 1.5K resistors and capacitors 0.1 uF, the band is in stop-10dB 500 Hz to 2 kHz. The depth and breadth of the reaction can be slightly adjusted to a value of 0.5 R and adding some resistance at the C-values,If the circuit is an operational amplifier is used as a bandpass filter, the response should be reduced to avoid oscillation.

The automatic door handle alarm circuit gives a audible alarm and glows a LED when somebody touches the handle of the door. The circuit is latching type and continues to produce sound until it is switched off.


The transistor Q1 is wired as an astable multi vibrator whose output is used to bias transistor Q2 to conduction. As a result the transistor q3 and LED are in OFF state. When someone touches the handle, the capacitance of the human body damps the oscillations of Q1.The cuts the biasing of Q2 and it goes OFF.As a result the current flows to the base of Q3 , it conducts and LED glows. If the switch S1 is ON the transistor pairs Q4&Q4 which is wired in the latching mode is triggered and the Buzzer Z1 is activated. When the person removes his hand from door handle the LED goes OFF but the buzzer continues to beep. The only way to mute the buzzer is to open the switch S2. All capacitors must be rated 15V.

A 9V battery or 9V DC power supply can be used to power the circuit. To make L1 wind 25 turns of 0.4 mm enameled copper wire on resistor R2 and solder the ends of the wire to the resistor leads. This unit will stand for the R2 as well as L1 because both are parallel in the circuit. A readily available 10mH inductor can be used for L2. Connect the point A in the circuit to the door handle using a long wire.