Saturday, July 26, 2008
Monday, July 21, 2008
Information about digital logic families is the commonly asked question in many entrance exams for embedded training course. The most popular digital logic families are transistor-transistor logic (TTL), emitter-coupled logic (ECL), metal-oxide semiconductor (MOS) and complementary metal-oxide semiconductor. Now let us see about the features of each of these families.
- The TTL is a logic family that has been in operation for a long time and is considered as standard. They consume more power than an equivalent CMOS device but consume less power when compared to ECL.
- The ECL logic family has an advantage in systems requiring high speed operations. The ECL gates use differential amplifier configuration at the input state. They usually operate with negative power supplies.
- The MOS is suitable for circuits that need high component density.
- The CMOS is preferable in systems requiring low power consumption and they are used for VLSI design.
Saturday, July 19, 2008
- The Small Scale Integration devices contain several independent gates in a single package. The number of gates in SSI is usually lesser than 10.
- The Medium Scale Integration devices have about 10 to 1000 gates in a single package. They are used to perform specific elementary digital operations. They include decoders, adders and multiplexers.
- The Large Scale Integration devices have thousands of gates in a single package. They include processors, memory chips and programmable logic devices.
- The Very Large Scale Integration devices have hundred of thousands of gates within single package. They include large memory arrays and complex microcomputer chips.
Tuesday, July 15, 2008
Most of you would have learned Digital Electronics in your third semester. You may have heard about these memory elements which are used for storing binary information. The latches are nothing but most basic types of flip-flops. But the latches are level sensitive whereas flip-flops are edge sensitive. This is the basic difference between the two. Thus the change of state in a latch will occur even for an active high input (dc level) i.e., the latch will respond to the change in state when the clock pulse is still in logic1 which will lead to undesirable situation. The change of state in a flip-flop occurs only when their is a change in the clock input. Since the state of a memory element must change only there is a change in control input (ac level) we use flip-flops as storage elements in digital circuits instead of latches. I hope that you can know understand the basic difference between latches and flip-flops. The below image shows the clock response in latches and flip-flops. If you know any other differences then please post a comment so that others may know about latches and flip-flops.
Saturday, July 12, 2008
It’s true that “Failure is the stepping stone to success”. I have realized it practically when, I first started to build my electronic circuit ‘LED flasher’. I took the circuit from EFY magazine when I was in my 4th semester. It's a simple circuit using LM317 along with some resistors, capacitors, diode and LED. The output was to switch the LED ON and OFF for an interval of 15 seconds. The reason I took the ‘LED flasher’ circuit from EFY was because I was able to identify all the circuit components. After getting the required components from
Hope you would have you own blow while starting any process(in any field). Leave a comment regarding your first blow so that others can learn much from you.
Thursday, July 10, 2008
Monday, July 7, 2008
The reed switch is an electrical switch operated by an applied magnetic field. It consists of a pair of contacts on ferrous metal reeds in a hermetically sealed glass envelope. The contacts may be normally open, closing when a magnetic field is present, or normally closed and opening when a magnetic field is applied.
When a magnetic force is generated parallel to the reed switch, the reeds become flux carriers in the magnetic circuit. The overlapping ends of the reed become opposite magnetic poles, which attract each other. If the magnetic force between the poles is strong enough to overcome the restoring force of the reeds, the reeds will be drawn together. In our project laser based tracking system we used the reed switch for mouse click operation. Note : please be careful while bending the Reed Blade, don' t bend it near the Glass capsule, if you do so it will break. Leave about a 1cm gap and bend the Reed Blade.
Saturday, July 5, 2008
SENSOR 2 – LDR
A LDR or photoresistor is an electronic component whose resistance decreases with the increasing incident light intensity. It can also be referred to as a photoconductor. It is made of a high-resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. In short as light falls on it the resistance of LDR will decrease from normal conditions. Can be used as Night switch alarm, in counter circuit with laser beam to calculate the person entering into the door etc. LDR's of various sizes and shapes is shown below.