The Centenary Exhibition of the Madras University

But 1957 was something special. The Madras University had decided to celebrate its Centenary and that was also to be at this engineering site. True, the University had its Alagappa Chettiar College [for Textile Technology] in the adjacent compound -- still the Guindy college would play host for the event

A special canteen monstrosity was set up -- where you could get the dishes from slot machines at the drop of a token [which was a simple MS piece of one inch dia -- and nobody wanted to make a counterfeit token and Telgi was not yet born!]. The college portico became the ticket issuing booth where 10 to 15 students, at any time, gave away the entry permits at four annas a piece. The exhibition was sprawled over an area that was not less than 40 acres. Sure it was huge not meant to be browsed in a single afternoon

Principal Morley had set up set up a toy train that passed through Ariyalur [the incident for which the destination had become notorious and caused the resignation from LB Shastri, the then Rail Minister, had happened hardly six months before], Half Way House and a tunnel amongst other things. The main entrance to the exhibition was specially done by artists from the Kodambakkam industry, namely the big banner painters

All the labs kept open houses for the visiting public. The biggest draw used to be at the electrical lab. This time too. Where there was an obedient train that responded to the aural commands. There was a robot that answered any question in any language -- at the back office polyglots were running the show. One old man wanted to know when his daughter would get married. The all knowing robot responded without any hint of hesitation -- that the wedding would take place very soon -- but certainly following the discovery of a suitable groom!

At another room I had an exhibit. The city of Madras then had the only automatic signal at Egmore then. I was no doubt impressed by that and had made a working model. Next to me was the exhibit of [now Dr.] Ramani -- which was a scale replica of the Calder Hall [atomic] power house [of UK]. Atomic power stations were the in thing in that zamana

The star attraction was the show in the galleries of the so called X-Hall. Where the shows were organised once in about 15 minutes. There were three items. The first one was a device that rocked the cradle and played a lullaby [from the film Parasakti], whenever the baby refused to get into a slumber [yes, the baby was attempted to be put into slumber every 15 minutes]. The next item was called the Alibaba's cave. You have to play a certain tune on a designated harmonium-- only then the doors will open [sesame]. When the gates opened room lights would be dimmed so you may see the jewelled treasures inside in all their glory flooded with a bright reflected phosphorescent illumination! Viewers used to be cautioned not to force their way inside the cave. Y'day several went in without heeding to our advice -- and they never returned!

Who was the Congress President.. er.. of the Avadi Session?

But the most important one occupying the centre stage was something that annunciated the Presidents of the Congress, given the years of vintage. Why would anybody be curious as to be inquisitive to know who the President was at any given time -- is anybody's guess. Presumably the Congress Sessions and their Presidents were something to gossip about in those days. And possibly there was no opposition to count. Anyway I think we catered for about 31 years in retrospect of the Presidents. The years were grouped and appeared in one or often, more than one column. You have to tell in which all columns your chosen year appears. For each appearance in a column a corresponding switch was made on [at the back stage the operation lit a lamp for the benefit of the decoding expert]. When all the columns are gone through likewise the Congress President of the year got announced by the lighting of a corresponding photo amongst many displayed. Sometimes the President had the office for several years -- then the same photo came up for diverse selections though the decode had to be done for every case individually. 31 switches had been wired for this purpose at the back stage

Actually the years were coded in binary. That is how a five column matter can code 31 Presidents. At the back stage the volunteer manually added the weights for each column -- which were 1, 2, 4, 8 and 16 respectively. And he lighted the corresponding photo at the flick of the corresponding switch, again.

The exhibit did not impress many -- but sure I was excited. And I imagined the code or decode could have been effected with less pain by electrics [not electronics necessarily, since I had no knowledge of the same at that time]

Have you ever pondered on the staircase switch?

I used to be impressed by the simple staircase switch -- where two or more switches would behave as though each one controls the lamp by itself, independent of the other switches. Invariably my quiz to students always included the so called mutually exclusive aspect of the operation of these switches -- but never had I discovered any student even remotely being inquisitive

Now back to the Congress Presidents Exhibit. An examination of the contents of the groupings indicated the operation of the first switch determined if the chosen subject was included or not in the first group, the second in another group and so on. Not surprisingly groups in the above coding scheme had each 16 entries

The Great Indian Calendar Trick

The same trick I was to do for Sweta much much later -- on a sheet from a calendar [For Sudha or Vijay it was not clever enough nor would they accept paper solutions]. You think of a date [zero less than date less than or equal to 31]. Say if the date is shown in group A. If it is there it was inferred the chosen date is 16 or more and an arrow moved your search 16 position away, to square 16 to be exact [if not it stayed at default zero position]

Similarly if the chosen date is found in the second, namely B column, a different arrow moved another eight positions forward and so on. When it no longer moved the arrow was already on the chosen date. Simple and it impressed the kids

I did a similar model to demonstrate the Napier Bones -- may be it may still be located at the attic at Saidapet. No mechanics. No electronics. The gadget simply worked. That's all!

However the Congress Presidents model was to go for the next Teynampet exhibition. I think Prof Balu was in charge. I must have explained my suggestion to mechanise the same to him -- hesitantly, without any motive for an implement. In the next few days the Prof had ordered a set of switches -- in fact five of them each having a bank of 16 change over contacts. That must have been luxury at that time -- the contractor must have charged for all the silver contents in the contacts!

Though we had the choice to deploy 16 switches [all operating or de-operating at the same time] the first four columns used only 1, 2, 4, and 8 contact sets respectively. Only the last column mandated all the 16. But that is a minor triviality -- but you could deploy any switch anywhere, wasn't that great?

The good news was that the model was now fully automatic and not semi-auto

A Binary Mux and Demux

Two years later I was out of the college. I wanted to repeat the President model. Since I had no dough for ordering the silver contact switches I fabricated a compromised outfit that functioned. How will I wire 31 lamps that may be lighted from the outputs of the switches? Obviously buying 31 or 32 lamps was beyond my capacity

So I devised another gadget that merely swept all the outputs [manually though] and discovered which one was excited. Padmanabhan, my junior in the college happened to be present when I was testing the same [it must have been the June of 1959] in the half finished construction of the house at Saidapet

Looking back now what I had devised were a binary coder and a decoder [or a five bit mux and a demux]. It looks so simple now. Nobody would even reflect if such a device was ever to be fabricated -- because they are now available as ready to use hardware