Most people will be familiar with satellite dish antennas in the shape of a parabola. Whereas a true parabola has a precise mathematical definition, most likely approximating to this shape and with a reflective surface can be used to“catch” sound.
Base on the picture above we know how to catch sound by means of “sonar we call it” – during my early year in college we become – let say: having fun or interested of what other people are talking a far from us, so we desided to improvise the technology during the world war…☺, and we develop the sonar telescope.
Sorry, I only have one picture of the project which already in the picture above. Anyway lets get back to the topic. Below is the circuit diagram of the sonar telescope.
Here is the block diagram below. Thanks to Autocad we can Redo Details,
In order to adequately amplify the input signal, the circuit consists of both preamplifier and audio amplifier stages. Referring to the full circuit diagram for the Sonar Telescope, the microphone, MIC1, is powered via resistor R1, which behaves as its load. The signal produced by MIC1 is a.c. coupled via capacitor C1 to the base of npn transistor TR1. The network around TR1 forms the preamplifier stage. Resistors R2 to R5 bias it for linear amplification. The BC109C chosen is ideal for low noise audio applications such as this, offering more than adequate gain, although other general purpose high gain npn transistors will work in this design. Any instability at this stage could distort signal processing throughout, hence the inclusion of capacitors C2 and C4. Capacitor C6 provides thermal compensation in the emitter circuit. Capacitor C3 and resistor R6 decouple the stage from disruptive power supply variations.
Capacitor C5 couples the preamplified signal to level (Volume) control VR1, from where it is fed via C7 to IC1 input pin 3. The circuit around IC1 forms the audio amplifier stage. Capacitor C8 acts as an audio filter and the value quoted can be varied up to several nanofarads. The LM386N(you can change this for much more good) audio amplifier i.c. has been chosen for IC1 because it is relatively easy to use and provides a smooth gain of over 200 (set by capacitor C9).
Ensure that the electrolytic capacitors and the semiconductors are inserted the correct way round. Use a socket for IC1, but do not insert the i.c. until the assembly has been completed and checked for accuracy. Note that the microphone insert is also a polarised device. Its case is internally connected to one of its pins, to which the 0V connection should be made. The wiring to the microphone should not exceed about 140mm in length.
The circuit should be fully tested before housing it. It is suggested that the main amplifier is tested first, without it being connected to the preamplifier. When the amplifier is powered, touching the middle lug (wiper) of VR1 (or pin 3 of IC1) should produce a coarse buzz at. Most of the external components for IC1 are needed for stability. Capacitor C13 caters for variations in the supply voltage and is used on the main amplifier board, as opposed to the preamplifier board. With IC1’s output impedance being 64 ohms, headphones are preferable to speakers. This also avoids the problem of “telephony” which can hamper performance.
The prototype was built on two separate stripboards for several reasons. Firstly, both stages are isolated, which helps minimize problems with spurious feedback, whilst making fault-finding easier. Secondly, because the project is handheld, compactness is an issue. Two smaller circuit boards can be used to make the most of the available space. Assemble the boards in the usual order of ascending component size, having first correctly cut the tracks where required the output. There should also be a low level hum at the output, confirming that the amplifier is working. Once the amplifier has been proved, the preamplifier can be connected to it. Key test voltages can be measured with a multimeter. Initially check if the microphone is picking anything up by gently tapping it and hearing the output. The prototype easily picked up ambient sound with VR1 set to less than a quarter of a turn.
Because the circuit is extremely sensitive, anything picked up by the microphone can result in an ear-splitting whine dominating the output. This can be resolved by thoroughly insulating the microphone’s bare metal surface using insulating tape.
To my classmates/friends who made this project successful. To my Professor, Engr. Cilot. His crazy Prof. – he asked to built the project to listen from the next building which all of the nursing students are staying. Kind a stalking. To Raph, and Dave – thank you