MadSci Network: Computer Science
Query:

Re: I want to build a simple calculator for my science project. How?

Date: Thu Mar 15 11:16:25 2001
Posted By: Michael L. Roginsky, Staff, Avionics, Honeywell Defense Avionics
Area of science: Computer Science
ID: 984107587.Cs
Message:

Hello Navarra:

Calculators are based on Very Large-Scale Integrated (VLSI) microcircuits 
composed of logic and state transition elements and microcoded so that 
with a few pushes of buttons one can accomplish marvelous results. Our 
biggest drawback with microcircuits is the access needed to inject and 
extract signals in a small package. http://encarta.msn.com/find/Concise.asp?ti=0494F000

Computers unlike people prefer to calculate numbers using binary bases 
because of the fundamental logical values are 0 and 1 (forget for the 
moment fuzzy logic). Serial to parallel shift registers demonstrates how a 
number can be multiplied by two with a single shift from the least 
significant bit towards the most significant bit. Let us assume an 8-bit 
binary shift register. Bit 0, the least significant bit, is loaded with a 
logic level 1, or high. As it is shifted toward bit 7, it is incremented 
by the power of two on each shift. So we start with 1, shift by one and 
the value becomes 2. The next shift the value becomes 4, and so on until 
the last shift produces 64. One additional shift produces 0 unless that 
bit is carried around to bit 0, in which case its value is one again. Look 
at this site for specifications of a typical binary shift register:
 http://www.ednmag.com/reg/1995/010595/01di6.htm#fig1 http://www.fairchildsemi.com/ds/MM/MM74HC594.pdf

At one Internet site I found has pictures of very simple digital circuits:
 http://www2.pct.edu/homepage/staff/rstull/DIGITAL/DIGITAL.HTM

I also found another site you might look-up:

www.hobby-electronics.com/Counter10-100-1000.htm

It describes 3 low power common CMOS chips hooked-up to give a count 
indication of 10s, 100s and thousands of pulses at the input. If you used 
a 5-volt power supply and 470 ohm resistors to limit current for the LEDs, 
the outputs give a visual indication of the number of 10s, 100s and 
thousands.

A third and better site shows an actual counter circuit with leds:

www.interq.or.jp/japan/se-inoue/e_ckt14.htm

Exercise care when handling integrated circuits: they are very susceptible 
to Electro-Static Discharge (ESD). In a dry day a person may easily 
accumulate 5 to ten thousand volts by shoe-to-carpet friction or polyester 
fabric friction. These voltages are hardly noticeable to us but very 
destructive to the tiny components and micro-traces inside the silicon 
chip. Always place your unprotected parts on a conductive surface that is 
grounded. Be sure to place a hand on that surface to equalize your body 
potential before handling the chip. Do a search on the Internet for “ESD” 
and you will discover how important it is to prevent ESD damage.

Your MAD.SCI Micro.



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