Specifications for the Ultra Sonic Proximity Detector

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Proximity detector                James Ashley-Smith

                

Electronics AS coursework

Aim

To design and build a proximity detector for the rear of a car that is used when it is parking. The sensor’s main objective is to decrease stress for the driver and make the task of parking easier and quicker. The sensor will use ultra sound to detect close objects. Initially the project will produce a simple mechanism to portray the idea, which then can be developed. For example the feedback to the driver could just be a buzzer that comes on when the car is too close.

Research

I chose to use ultra sound in my sensor, because I have had no experience with the components so it would be a good research topic and hopefully prove to be interesting.  The transmitter sends out the high frequency pulses, which reflect off of objects and are detected by a receiver. The longer the time between the emission and detection the more the amplitude of the wave decreases. Also the waves are transmitted in a 20° arc, I was able to find these facts from Rapid electronics company whom sent the ultra sound part I requested.

I have also found out that the waves received will still have a low amplitude so therefore a low voltage so a form of amplification is needed.

The next slight hitch I found was that the vibrations from the transmitter were also being received along with the pressure waves, to limit this I mounted the ultra sound devices in a piece of polystyrene. I also need to proceed with another investigation in to how the ultra sound works exactly with real results.

Specifications for the Ultra Sonic Proximity Detector

In order for the project to work effectively, there needs to be set of parameters for the project to follow as it develops.

  • Firstly the sensor needs to read the surroundings accurately and must sound an alarm when any object is close the sensor, for this project this needs to be about 40 cm from the object. I chose this distance, because it is a safe distance for parking and allows access behind the car.
  • To achieve this goal the electronics need to work so the next parameter is in the circuit. When the receiver picks up the signal from the transmitter it has to amplify the voltage amplitude for the Schmitt trigger to switch. The value after the op-amp amplification needs to be at least 2 volts, which is great enough to switch the Schmitt Trigger.
  • I found that the receiver and transmitter could not be too close, because the receiver is also sensitive to vibrations. This means the two units need to be mounts at least 10 cm apart so the vibrations do not affect the received amplitude.
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Solutions

        I started this development process by drawing quite a detailed block diagram. This helped me understand the circuit and allowed me to think of possible solutions.

555 timer

The first solution that I through of was how I would build the ultra sounding unit. I decided that using a 555 timer was really the only clock mechanism that would work easily and effectively, I have also used them before which is an advantage so it is probably best for the job.

Amplification

Next I thought about the amplification system I would use, this had to give enough ...

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