Week 7: The Proximity Sensor

Objective: To identify about and research about sensors

Analysis/Procedure:

There are many type of sensors currently being used nowadays. In this project, I need to find a suitable sensor that suitable for the speedometer. This components is the most important part. The sensor must detect the narrow and thin needle of the speedometer. My idea of the position of the sensor which will be placed on the speedometer display:

Below is the suitable sensor that I think could integrate with the speedometer. 

1. Proximity Sensor

• A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target. The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance. Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

• One of the application of this sensor is on a modern smart phone. For example, if there is an outgoing or incoming call on a smart phone and a person will start moving the cellphone towards his or her ear to listen to the other person, the device’s proximity sensor detects that the phone is very close to his or her face. The proximity detector signals the motherboard to disable the phone’s touch-sensitive display to prevent the person inadvertently activating an icon on the screen with his or her face. When the person move the phone away from your head, the proximity sensor detects the change and reactivates the touch-sensitive display.

In term of this project with the proximity sensor, if the proximity sensor detects a needle crosses the sensor it will send a signal to the PIC and automatically sends an SMS through the GSM modem.

Week 6: The Speedometer

Objective: To identify and research about the speedometer.

Analysis/Procedure:

Speedometer or a speed meter is a gauge that measures and the instantaneous speed of a land vehicle. Otto Schulze, an inventor from Strasbourg, filed the first patent for the eddy-current speedometer in 1902. Schulze conceived of the revolutionary device as a solution to a growing problem. Cars weren't only becoming more popular, they were also traveling faster. The average automobile's top speed just after the turn of the 20th century was 30 miles per hour, slow by today's standards but sizzling fast at a time when much of the world still moved at the leisurely pace of a horse-drawn carriage. As a result, serious accidents began to increase dramatically. Below is an example of a speedometer.

There are two types of speedometer for land vehicle. 

• The first and widely used is the mechanical speedometer. The speedometer is made up of two sections, the odometer which records the miles and the speed indicator. The odometer is quite simple, a simple gear train which takes a given number of turns of a tire and gears those turns down to equal one turn of the tenths wheel. Simple gearing. The speed needle is quite different. It works on magnetic fields. Connected to the cable is a magnet on the very end, usually in the sape of a disc. Close to, but not touching, is an aluminum disc. The magnet spins and genenerates eddy currents in the aluminum disc which produces a magnetic field in the disc, which tends to drag the aluminum disc to spin with the spinning magnet. There is a spring which works against the movement of the needle. So, the faster the magnet spins, the more the aluminum disc tends to be dragged along, resisted by the spring. So, the faster the spin, the higher the needle reads. In essence, it is a rate meter, which indicates the rate the magnet is spinning. Below is a mechanical speedometer example:

• Second is the electronic speedometer. Many modern speedometers are electronic. In designs derived from earlier eddy-current models, a rotation sensor mounted in the transmission delivers a series of electronic pulses whose frequency corresponds to the (average) rotational speed of the driveshaft, and therefore the vehicle's speed, assuming the wheels have full traction. The sensor is typically a set of one or more magnets mounted on the output shaft or differential crownwheel, or a toothed metal disk positioned between a magnet and a magnetic field sensor. As the part in question turns, the magnets or teeth pass beneath the sensor, each time producing a pulse in the sensor as they affect the strength of the magnetic field it is measuring. A computer converts the pulses to a speed and displays this speed on an electronically-controlled, analog-style needle or a digital display. Below is the electronic speedometer example: 

Conclusion:

The mechanical speedometer is cheaper and more practical then the electronic speedometer. To build this project, I have decided to choose mechanical speedometer. But there are few problems which I will be facing:

1. How to install the sensor to the speedometer?
2. How to simulate speedometer, when the meter is working mechanically?

Before going any further, I need to do some research about sensors.