Research
Through analysis I realised that there is a problem when someone thinks that they have closed their refrigerator door and do not really notice the fact that they have left it open. Therefore I am going to produce a product that when a refrigerator door is left open for too long a buzzer will sound alerting to the fact that the door has not been closed properly and then when the door has been properly shut the buzzer will stop bleeping automatically. I think about a fifteen second timer is probably a suitable period of time because I timed myself as to how long it took to remove several items out of the fridge and found that it took me about ten seconds, it depends of course on what you are removing from the fridge but on average the door does not have to remain open for longer than fifteen seconds.
The Circuit
The circuit above is a circuit which will be based on my final circuit; I am using a light dependant resistor because when a fridge is opened a light comes on and so when the light dependant resistor picks up the trace of light the 555 timer will start and after fifteen seconds of the light dependant resistor picking up light the buzzer will sound, so indicating that the fridge door has been left open.
The Light Dependant Resistor
If the control situation requires different levels of light this is likely to be the device used. The light dependant resistor is an analogue device and so its output is variable. However, it can be connected directly into the digital input connections of the interface. If different light levels need to be detected it must be connected to the analogue inputs of the interface. A battery can power the light dependant resistor and with my circuit that is the only possible way! The astable circuit will probably suit my circuit the best because when the fridge door is opened a beep is sounded until the door is shut.
The 555 Timers
Creating a Pulse
The 555 is made out of simple transistors that are about the same as on / off switches. They do not have any sense of time. When you apply a voltage they turn on and when you take away the voltage they turn off. So by itself, the 555 cannot create a pulse. The way the pulse is created is by using some components in a circuit attached to the 555. This circuit is made of a capacitor and a resistor. We can flip a switch and start to charge the capacitor. The resistor is used to control how fast the capacitor charges. The bigger the resistance, the longer it would take to charge the capacitor. The voltage in the capacitor can then be used as an input to another switch. Since the voltage starts at 0, nothing happens to the second switch. But eventually the capacitor will charge up to some point where the second switch comes on.
The Pins
Batteries
Without a power source no electric device will work, so the choice of power source is important. There is a very large choice although the power source I will be using is a battery. Batteries provide a very safe source of electrical energy and are the most likely power source to be used in an electronic product like mine. They come in various dimensions and have different voltage levels and properties, which are best, suited for particular uses. The battery, which is probably best for my circuit’s the one below.
The battery is not very expensive and allows maximum durability, which is why I do think it is best for my circuit.
The main problem now is the fact that there is a continuous bleep, and if the person wanted to clean the fridge this would become very annoying so to prevent this a manual override switch should be placed in to allow this beeping to cease. To notify the person that they have turned off the circuit the best thing to do would be to have a led to light when the circuit is off but when the circuit is turned back on the led is automatically turned off.
Switches
Switches can direct the current around the circuit by re-routing or breaking the connections that make up the circuit. There are a large number of switches but the one which would probably be best with my circuit is the single pole double throw, this type of switch can offer a choice of two directions for the current to take depending on the position of the pole. The other alternative is the single pole throw, this type of switch can only make or break a circuit.
The battery is not very expensive and allows maximum durability, which is why I do think it is best for my circuit.
All the things I researched are all needed to produce my electronic product.
