Fifty Years in Engineering – Part 2
Fifty Years in Engineering – Part 2
By: Stewart Da’Silva
Senior Designer, Product Design
29th March 2017
In my previous blog, I attempted to explain my journey of manually designing Printed Circuit Boards (PCBs) but, as always, time marches on and the world of taped artworks was consigned to history’s bin…
Around 1978, I started my ‘career’ in Computer Aided Design (CAD).
Racal-Redac’s Redboard was the first CAD system that I used; it was also the first fully integrated PC-based workstation that allowed for small single and double-sided PCBs to be designed. To compliment this, there was Redlog; a schematic capture software package. Although at this time, the main schematics were still hand drawn by tracers from an engineer’s ‘fag packet’ sketches.
Data entry was a manual task. A print was taken of the original schematic and on this print, all components were assigned pin numbers (e.g. resistors were designated pins 1 and 2). Then one person marked off and called out the connections whilst another typed the data onto a 51/4 inch disc cassette (floppy disc) to create a netlist. This netlist together with the addition of a manually created component list could then be used in the generation of a PCB. This data then had to be rechecked manually… a time-consuming task!
Apart from the PC-based Redboard, I did 90% of my work on Racal-Redac Maxi and Mini workstations, which were based on a DEC PDP11/34 16 bit mini-computer system.
Each designer had their own 10 megabytes read/write working discs… yes, you read that correctly… 10 megabytes; it had to be loaded into the 19” rack like computer. These RL02 drives were approximately 30 centimetres in diameter and were quite hefty!
Both the Maxi and Mini workstations consisted of a bulky monochrome monitor and a line printer. The first task, when your shift started (yes shiftwork!), was to load your RL02 disc drive into the PDP11/34 and then boot up the system. Next task was to login via the line printer and then your PCB start dump could be called in.
Much like today, the components and connections – ‘rats nest’- as it was termed in those days appeared on the screen. There were a couple of major differences from today… the image on the monitor’s screen was monochrome. To differentiate different trace width, various line patterns were used: solid, dash-dot, dash, dot etc. As you can well appreciate, it was pretty mind blowing… especially if you were on a 5 a.m. start!
The working environment left a lot to be desired as each Maxi/Mini was situated in a small darkened room, the only light in there emanated from a small shielded lamp that enabled you to read the printer and, of course, the monitor screen. The basic idea was to eliminate any distracting reflections appearing on the monitor screen. It also meant that the designer was on his own, with only the machine for company.
The second major disadvantage was that all placement and routing was carried out on a 25 thou grid (Data Structure Unit), this was fine for 99% of components as the boards were a mixture of discrete and dual-in-line integrated circuits (TTL being the order of the day!); but if a ‘D’ type connector was called up it presented a problem. Then, as now, ‘D-type’ connectors were dimensioned in 1/64ths of an inch, this made the component ‘off-grid’. To place the pads and route to them, these off-grid components had to have a special ‘off-grid’ programme written. A punch tape was created to give X-Y coordinates to the photo-plotter so that it could move the plotting head to the desired positions to plot these special pads. This in itself created yet another problem; the checking procedures could only check points that fell on the basic DSU grid, meaning, that you could only see the results of your programme once the plot had been completed. Inspection of this completed plot revealed if the clearances were correct or not. As the writing of these programmes, although not too difficult, was still a pain – it was felt that one person should be responsible to create them… and yes… it fell to yours truly!
Racal-Redac brought out a new software package: Cadstar, which, for the first time, was an affordable PC-based software for an individual or small design office. With this in mind, I left my then contract design house and with a work colleague started our own design house: GS Designs.
Apart from its affordability, Cadstar was a leap forward as far as users were concerned. One of the most important innovations was the departure from the basic DSU to a one thou grid for placing and routing, to all intents and purposes, the system gridless. No more off-grid programmes to write!. Another feature was that the system had a colour monitor that enabled multi-layer boards to be designed with comparative ease. There was also a new important step as far as preparing gerber data was concerned. A preview of what the actual end result would be could be observed for the first time. The buzz phrase was ‘WYSIWYG’ – ‘What You See Is What You Get’ this obviously lessened the risk of errors being made.
Around this time, it was decided that maybe engineers could be trusted enough to create their own schematics – Orcad schematic capture being the software of choice as this was the favoured university software package of the time. Orcad could generate a netlist that was compatible with most popular PCB software packages, Cadstar being one of them.
We continued to use Cadstar, although I did flirt with PCAD, Cadnetics and Cadstar’s big mainframe brother, Visula. Cadstar still remained the main PCB software until experiencing designing with Pads software. At the time, Pads was more user-friendly and it had more options regarding PCB design than Cadstar so… we are still using it.
Read part 1 of Stuart’s blog here.
Further Reading
