Integrated Circuits

Integrated circuits are large circutis made up of capacitors, transistors, diodes and many other components on a single wafer thin piece of silicon. The sit in a case that is often named a 'chip'. ICs have quite a few legs and are prime examples of semiconductors. They are digital components and some can produce very complex effects. Most ICs are specialised, they perform a specific function and because of this there are millions on the market. I will therefore, just go through a few ICs that will be used in some of the projects that will soon be publised on this site. Note: There are two main types of ICs: TTL (Transistor, Transistor Logic) and CMOS (Complementary Metal Oxide Semiconductors). CMOS ICs are more at risk from static than TTL ICs, however this is usually not a problem and CMOS ICs run on a wde variety of voltages 3V-15V. All these circuits will use CMOS ICs.

NE 555 Timer

The 555 timer has to be one of the most useful ICs. It is in effect an IC that emmits pulses of current in logic 1 and logic 0 formats. The properties of these pulses (Pattern, time on/off etc) can be altered depending on how the 555 timer is connected up. Thre are two main modes of operation for the 555 timer: Astable mode: Emmits a series of on/off pulses when triggered, the time on and off will be the same. Useful for producing a 'siren' effect on a buzzer and flashing LEDs. Monostable mode: When connected to a power supply the 555 timer will go into 'sleep' mode. It will remain in logic 0. When triggered it will go into logic 1 (on) for a set period of time and then switch back off into logic 0 again. Depending on how it is connected a 'time on' or 'time delay' can be made. Useful for egg counters etc.

741 OP-AMP (Operational Amplifier)

The 741 OP-AMP is a very useful IC, it will will multiply the voltage at the input by a scale factor, however the end voltage cannot exceed the power supply voltage. They are very sensative with a high voltage gain and are versatile enough analouge AC and DC amplifiers with a linear output. The OP-AMP has two inputs called the inverting and the non-inverting indicated with a +/- sign, this must not be confused with the battery polarity. The '+' indicates the inverting input and the '-' indicates the non inverting input. The difference between the two inputs is amplified. There are three configuration in which the OP-AMP can be used: An inverting amplifier - the output is inverted: + becomes - and vice versa, so 2V amplified to 6V would become -6V. A Non-inverting amplifier- the input is just amplified and a comparator- the OP-AMP will compare the voltages and make an output dependant on the voltages i.e when Va>Vb etc. Gain for an inverting amplifier= -Rf/Rin (Rf is the 'feed back reistor' value, and will become apparent when you see an OP-AMP circuit. Gain for a non-inverting amplifier= Rf+Rin/Rin.

4017B Decade Counter

The 4017B is an example of a Decade counter, decade counters enable a clock pulse to be counted or devided. The 4017B has 10 output pins, when pin 14 is connected to an astable 'clock' input and pins 16 and 8 are connectec to a suitable power supply- each of the ten outputs will go off in turn. If LEDs were connected to the outputs then a strobe lighting effect would be created. The IC can be reseted via pin 15 and the output would then count from pin 11- the first output all over again. The 4017B can also devide a clock input via pin 12. Pin 12 will devide the frequency of the input by a factor of 10. Thus if one 4017B is connected up to count and pin 12 is connected to pin 14 (clock input) of another 4017B the outputs will flash ten times slower. This pattern can be repeated and a very accurate clock output can be produced making a long interval timer.