25-07-2012, 02:36 PM
LISTENING BUG
[attachment=28902]
General Description
It is a simple inexpensive and hi-fi device for listening to the conversation going on in an adjoining room or
for the parents wishing to keep a strict, vigil on the activities of their children through the sound in children's room. It is one evening project for an experimente.
How it works
The condenser microphone picks up the sound signals (even at a distance of 5 meters from the mike),
and converted into electrical variations, which are amplified by the op-amp IC 741 used in the inverting
mode with a single supply using divider network of resistors. Varying the feedback through 2.2M; preset
can set the gain of IC 741. The output of IC 741 is further amplified using transistors BC 187/188 pair.
Construction
First of all let us consider a few basics in building electronic circuits on a printed circuit board. VISHA Kit
boards also come pre-drilled and with the outline of the components and their identification print. You
should place on the board the resistors, the capacitors, and the transistors & make sure that the electrolytic capacitors & diodes are connected the right way because they are polarized.
Warning
VISHA kits are sold as stand alone training kits. If they are used as part of a larger assembly and any
damage is caused, our company bears no responsibility.
Adjustments
This kit does not need any adjustments, [leaving Volume adjustments as per requirement]
A shielded wire should be used to suppress hum for carrying the output signal from the output of the
amplifier to speaker fitted in the other room. Alternatively, from point C onwards, the amplifier
can be dispensed with by feeding the output of the IC 741 to the pick-up point of an ordinary transistor
radio.
The microphone used in this project is of the condenser type for greater sensitivity. The supply
voltage required for the correct operation of the LISTNING BUG is 9VDC we can use 9v battery.
[attachment=28902]
General Description
It is a simple inexpensive and hi-fi device for listening to the conversation going on in an adjoining room or
for the parents wishing to keep a strict, vigil on the activities of their children through the sound in children's room. It is one evening project for an experimente.
How it works
The condenser microphone picks up the sound signals (even at a distance of 5 meters from the mike),
and converted into electrical variations, which are amplified by the op-amp IC 741 used in the inverting
mode with a single supply using divider network of resistors. Varying the feedback through 2.2M; preset
can set the gain of IC 741. The output of IC 741 is further amplified using transistors BC 187/188 pair.
Construction
First of all let us consider a few basics in building electronic circuits on a printed circuit board. VISHA Kit
boards also come pre-drilled and with the outline of the components and their identification print. You
should place on the board the resistors, the capacitors, and the transistors & make sure that the electrolytic capacitors & diodes are connected the right way because they are polarized.
Warning
VISHA kits are sold as stand alone training kits. If they are used as part of a larger assembly and any
damage is caused, our company bears no responsibility.
Adjustments
This kit does not need any adjustments, [leaving Volume adjustments as per requirement]
A shielded wire should be used to suppress hum for carrying the output signal from the output of the
amplifier to speaker fitted in the other room. Alternatively, from point C onwards, the amplifier
can be dispensed with by feeding the output of the IC 741 to the pick-up point of an ordinary transistor
radio.
The microphone used in this project is of the condenser type for greater sensitivity. The supply
voltage required for the correct operation of the LISTNING BUG is 9VDC we can use 9v battery.