MadSci Network: Engineering

Re: What is the best place to start in designing a electronicly controlled swic

Date: Sun May 21 03:04:40 2000
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Engineering
ID: 957293643.Eg

Hi Jay!

Welcome to the hallowed halls of the CMOS experimenter! I'm glad to be 
able to help you. While I could just give you a parts list and circuit 
diagram, I respect your willingness to learn the how and why's of circuit 
design on your own.

The one book I would recommend highly, be you a beginner or well advanced, 
is the "CMOS Cookbook" by Don Lancaster. It contains a brief history of 
CMOS, then gets into the actual package types (4518 dual synchronous 
divide-by-10 counter, 4011 quad 2-input NAND gate, etc.) proper circuit 
design techniques, hints, tricks, clocked logic, sample circuits, and 
much, much more. It is available from various sources, being 
one, for about $22. I bought mine back in 1977, but a new (1997), updated 
version is now in print. $22 bucks may sound like a lot but, when you 
consider I have used mine for about 23 years and it cost me $7.95, that 
comes out to about 35 cents per year! Not too bad. Other books are 
available at places like Radio Shack. When you need to get very detailed 
specifications, you can go directly to the manufacturer. Texas Instruments 
( ), National 
Semiconductor ( ) 
and others, have on-line access to the latest info on their products 
including specification sheets, application notes (great resource - some 
include complete circuits for various applications; others discuss the 
theory of operation of Operational Amplifiers, Phase-Locked Loops, power 
supply regulation, and more). They also publish their own databooks which 
can be had in either soft-cover or CD-ROM for free or at a nominal charge.

I suggest you salvage an AT power supply from an old desktop computer. 
These power supplies are ideal for experimenting. They provide both 5 
volts DC and 12 volts DC. Also, get an 'experimenters breadboard' at Radio 
Shack, the one with the power supply banana plugs mounted on it. With one 
of these, you can plug multiple CMOS devices directly into the board and 
make your connections with 22 gauge hook-up wire. Get several colors. I 
use red for the power supply positive, black for the negative, and green 
for everything else. It makes it much easier to check your wiring and 
trouble-shoot the circuit. You can make changes to your circuit easily 
with a braedboard, and it keeps things relatively neat. Plus, it's a heck 
of a lot easier, less time consuming, and cheaper in the long run than 
buying sockets for your CMOS, mounting them on a circuit board and wire-
wrapping or soldering your connections. Once you've completed the design 
AND testing of your circuit, THEN you can make it permanent on a socketed 
circuit board using wire-wrapped connections. Later on, you can buy a kit 
and etch your own circuit boards on copper-clad fibreglass (also available 
at Radio Shack). With this process, you place circles and other shapes of 
an etch resist material, where you want to put your sockets and other 
components, and 'connect the dots' with a special etch resist pen. The 
circles, etc. come on sheets which you transfer to the board by 
positioning the sheet on the board and rubbing the back side of the circle 
with a ballpoint pen or other smooth-tipped tool. The circle will stick to 
the copper. Once you have your circuit 'drawn' on the board, the board is 
placed in the etching solution (ferric chloride - CAUTION! HIGHLY 
CORROSIVE!), which dissolves the uncovered copper; that which has no 
circles or lines over it. When the etching is done (you can tell by 
watching it dissolve the copper), you end up with a completed circuit 
board - ready for component mounting and soldering.
I use a computer to 'draw' my circuits to actual size, print it out on a 
laser printer, make a photographic negative of it, place the negative over 
a specially-coated photo resist copper-clad board, and expose it to ultra-
violet light for about 15 minutes. The ultra-violet light polymerizes the 
coating under the clear areas of the photographic film, making them 
impervious to the ferric chloride etchant. It's obviously a much more 
involved process, but the computer lets me draw much thinner (and 
straighter) lines than can be done with a pen, resulting in a much more 
compact and neat circuit board.
If I can be of more help, contact me directly at

Also, if you wish, email me a rough drawing of your circuit, with your 
component choices (CMOS part numbers) and I may be able to make some 
suggestions to improve it, or make it work if you're running into trouble.

Good Luck!

Your not-so-mad scientist,

Karl Kolbus  

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