Background.
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- The telephone system in Manila in 1976 was the old pulsed type.
- The lines connecting the various "central stations" were so limited that accessing a subscriber number was a chore in itself.
- One solution was for a telephone dialer to do the dirty job of dialing.
- Dialing meant having many numbers in queue. Inability to make contact with the current number would signal the next number to come to the current memory area, and so on.
- The number being dialed would appear on the led display, while the process simply rotates the dialing of a maximum of 16 numbers, each with 16 digit, inclusive of two possible PABX access numbers of 2 digits each (dialing from one PABX to another one and to an external line.
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The Work.
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- Microprocessors at that time was not readily available. Furthermore, they carried a certain myth around them.
- The project was undertaken using exclusively TTLs, OPAMPs, and bipolars.
- An active filter was constructed for the dial tone, and another for the busy signal.
- Each of the 16 numbers stored could be addressed by a 2-digit decimal number at the scratch pad, so that it was possible to dial more than one number at a time.
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Conclusion.
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- Needless to say, the product needed a big box.
- By the time, it could be brought to the market-place in 1977, a small microprocessor-based product came into the market.
- There was no way it could compete in the market, but it was a wonderful personal learning experience for me.
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