The Dtmf data collection system was developed as an inexpensive means of interrogating process control equipment. It used the "Tone Writer" method of sending the alphabet, including numbers and some punctuation marks. An analog to digital converter supported the voltage measurement for temperature, pressure and conductivity and a counter took care of the frequency measurements for flow and other a-c signals. There were signal conditioning circuits to convert the various

sensor outputs to a format that allowed reading in "real" units. These data were then transmitted by DTMF Tones over a standard telephone line and received using a "Tone Writer" that displayed the information on an LCD screen. The "Tone Writer" was connected to the telephone earpiece via an induction coil and a suction cup. The telephone keypad provided the means of selecting a function to be read by pressing an appropriate key. There is also an on board keypad and display for local readings for setting alarm setpoints and interrogating the functions. See DTMF.
 

The next data project was called "Blue Box" and  was developed to remotely interrogate equipment that purified cooling tower water with injected ozone. As with the DTMFequipment, a mix of analog and digital sensors were needed to monitor the various functions of temperature, pressure, conductivity, ORP, pH, etc. The interrogation was via PC, so project "Blue Box" included a modem, ring detect to pick the phone line and a port for local setpoint and data readings using

a handheld data terminal. A computer program at the "host" site controlled the automatic data logging by telephone, of 30 remote sites  twice per day. At each remote site there was a dialing circuit that called the "host" in an alarm situation, alerting an operator that a problem had occurred. Lights and an audio device on the remote panel would also activate during an alarm condition alerting an operator and showing the problem areas.
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The next step was to design an advanced data logger with an increased measuring capacity. This design features a "motherboard" and 8 signal conditioning card slots. Each of the conditioning cards have three sensor inputs that are interrogated via a processor module which is connected to a telephone or radio modem via its  RS/EIA232 data port. A host computer does the polling and storing of the card data, including the various alarm functions.

The alarm set point circuitry for each of the sensors is located on the signal conditioning cards.  In an alarm condition, the host computer will be immediately interupted the polling operation and log the alarm event. After the data are stored and the host operator is alerted to the alarm condition, the computer will return to it's normal operational mode. The first application of this unit for Ham Radio use was in an earthquake monitoring network.
 
 

A word about the host computer. It was a Sharp 5000 laptop with an onboard printer and battery supply. The data storage could be either in the magnetic bubble memory module within the computer or an external dual "floppy" drive accessory. The program for the logging function was written in GWBasic and a connection to a phone line or a radio was done via modem and the RS/EIA232 data port. This computer having a printer, battery supply, and memory made it a "natural" for portable and field monitoring use.