The HP9100A/B Scientific Calculator (Cont'd)
The Remote Environmental Telemetry System
In 1970, we took the same HP9100 calculator, repackaged it, and significantly upgraded its responsibilities. Not only did it continue to control the eight environmental control chambers, it also became the centerpiece of a remote environmental telemetry system that stretched 200 miles from the Lincoln National Forest in the north to the Plant Science Center south of Las Cruces, New Mexico.
In both instances, sensors were placed at various heights in the plant canopies to accurately record their various microclimates throughout the year, the only difference being that the top of the cotton canopy was approximately four feet tall at its highest and the pine forest canopy was 70 to 100 feet tall. The white container in the right photograph was a surplus missile warhead container that we obtained from White Sands Missile Range. These lockable containers proved necessary to protect the telemetry stations from hunters.
The data returned to the lab was not only recorded by the HP9100 calculator, but could also be sent simultaneously to one or more of the environmental chambers so that the external environment could be recreated within the chambers themselves. Every few seconds, the HP9100 readjusted the settings in the eight environmental control chambers. Interleaved with this activity, once every few minutes, the HP9100 calculator would query each of the remote telemetry stations.
However, in our case, the Bell modems that were available weren't usable. They drew far too much power and wouldn't fit in our size constraints. So we built our own modems from scratch, designing the UARTs (using TTL flip-flops and NAND gates) and tone decoders, and having them integrated into the remote telemetry station circuit boards, all of which were hand wire-wrapped by the wildlife and biology students.
In order to connect these "modems" to the telephone network we had to undergo a reasonably rigorous certification process by Mountain Bell to guarantee that the modems met all Bell standards. In spite of the pro forma procedures associated with this certification, the local Bell people were always very helpful. But then again, we were paying them a great deal of money each month.