Wednesday, 13 October 2010

Electric Motor

There is no basic difference between the construction of DC motors and generators. Rotating machines of this type must have the following basic features.
1.       A magnetic field system
2.       A system of conductors
3.       Provision for relative movement between the field and the conductors
In most DC machines the magnetic field is set up by the stationary part of the machine, which is called the field system. The commutator and the conductors which form the armature winding, are mounted on the rotating part of the machine.
The body of the machine is a hollow cylinder of cast steel called the yoke. Which forms the basis for construction of the machine and is part of the magnetic circuit. Fixed pole pieces made of solid steel or iron are fixed inside the yoke.
Each pole has one or more field windings placed over it to produce a magnetic field. There is always an even number of poles.
Then there are the armature windings of the DC machine which are often very complex, there are two basic types.
1.       Wave windings – these tend to be high voltage, low current windings, and always have two conducting paths in parallel.
2.       Lap windings – these tend to be low voltage high current windings, and have as man conducting paths in parallel as there are poles. 
The ends of the winding are brought out of the slots at one end, where they are connected to the lugs on the commutator by welding or soldering. A typical commutator will be made up of many hard drawn copper segments each one insulated from the other with mica.
The completed armature is mounted on bearings, often supported by end plates mounted on the yoke. The carbon brushes are mounted so that the pressure exerted by them on the commutator can be adjusted, and so that the pressure will remain reasonably constant as the brushes wear.
Below is a picture of a DC motor with a spilt yoke, showing much of the above descriptions. 

Monday, 4 October 2010

Micro Set up

I created this blog post, just to show you all how i set up my micro project for college last year, it composes of two boards, the one directly below is a input and output board. 
the other one is where the actual micro that is programmed is contained.
The 3rd picture is them connected together and to a power supply, while the last picture shows them connected to a PC by a serial port.

The serial ports where the micro is connected to the PC 

Friday, 1 October 2010


Static RAM (SRAM)- Static RAM is a type of random access memory that is used to hold data without external refresh circuitary to keep the data together. The memory is held for as long as there is power supplied to the circuit.
Dynamic RAM (DRAM)- Dynamic RAM only holds data if a refresh circuit has continuous acess to the Dynamic RAM. The refresh circuit reads each memory cell even if the cell being scanned has no information stored in it, this refreshes the memory contents. this process is repeated hundreds of times per second. If this process is not repeated, the Dynamic RAM loses its memory even if power is still supplied. This process gives the name Dynamic. All PC’s use Dynamic RAM for their main system memory.
Static RAM and Dynamic RAM compared.
·         Static RAM doesn’t require external refresh circuitary to help to retain the data stored whereas dynamic RAM needs external refresh otherwise the data stored is lost.
·         Static RAM is faster than Dynamic RAM
·         Dynamic RAM is more complicated than Static RAM due to the external refresh circuits required
·         Dynamic RAM is cheaper than Static RAM
·         Static RAM is larger than Dynamic RAM because Static RAM is made up of four or more transistors per bit whereas Dynamic RAM uses one transistor and a capacitor.

Read Only Memory (ROM)- ROM is a type of memory that can only be read and is used in PC’s. the data stored in ROM is permanently present with or without power connected. ROM can be removed, stored for a long period of time and replaced without the data being lost which makes ROM non-volatile, whereas RAM is volatile memory.
Parallel ports- a parallel port is an interface found on computers and are used to connect peripherals to the computer.