S.L. Sargent, W.S. Dey and D.A. Keefer, Illinois State Geological Survey, 615 E. Peabody Dr., Champaign, IL 61820. This research was supported by the Illinois Groundwater Consortium, Carbondale, IL, 62901.
The use of a flow-activated automatic sampler at a remote research site required personnel to periodically visit the site to collect samples and reset the automatic sampler. A cellular telephone was modified for activation by a datalogger to inform researchers when trips to the research site were necessary to collect samples. Both the power switch and the speed dial button on the telephone were bypassed and wired to a relay driver. The datalogger was programmed to compare values of a monitored environmental parameter to a target value, in our case flow rate in a drainage tile. When the target value was reached or exceeded, the datalogger pulsed a relay driver activating power to the telephone. A separate relay activated the speed dial, dialing the number of a tone-only pager. The use of this system has saved time and reduced travel costs by reducing the number of trips to the site, without the loss of any data.
We were monitoring tile drainage at a field site approximately 55 kilometers from our office. An automatic sampler at the site was activated by a datalogger when water flow in the drainage tile increased above a specified rate. The activation of the sampler required personnel to visit the site to collect samples and reset the automatic sampler. Instead of visiting the site every time we thought there may have been enough precipitation at the site to activate the sampler, we modified an inexpensive cellular telephone to call a tone-only pager when the sampler was activated.
Several instrument manufacturers market telephone or radio links that allow communication between an individual and a datalogger at a remote site. These devices vary in complexity and expense, and have their place in some research settings. In this note, we present an inexpensive option that may be suitable where the researcher needs to know whether a change in one or more monitored parameters, such as a change in flow conditions, temperature, etc., warrants a trip to their research site.
A cellular telephone (Motorola1 AC-250, Motorola Libertyville, IL1) was modified for control by a datalogger (Campbell Scientific CR10, Campbell Scientific Inc., Logan, UT).
The power switch and speed dial button on the telephone were bypassed and wired to a relay driver (Campbell Scientific A21REL-12). The relay driver was wired to the datalogger.
Reference to a brand or company name does not reflect endorsement of particular products by the Illinois State Geological Survey or the State of Illinois.
To modify the telephone, the telephone housing was opened to gain access to the circuit board inside. The power switch was located on the circuit board by correlating its position to the power button on the outside of the telephone housing. When the power switch is pressed, two electrical traces on the circuit board are connected completing a circuit, which turns on or off the telephone. Traces on the circuit board leading from either side of the power switch were followed to accessible locations on the circuit board. A separate 22 gauge lead wire was soldered to each of the two traces to the power switch. The same operation was performed on the speed dial button (Fig. 1). A hole was drilled through the telephone housing near the phone cord for the new wires to exit through. After threading the four wires through the hole, the telephone housing was resealed. The two lead wires from the power switch were attached to a relay driver. One wire was attached to the common terminal, the other wire was attached to the normally open terminal. A third wire was attached linking the control terminal of the relay driver to a digital input/output (I/O) port on the datalogger. The same operation was performed on the lead wires connected to the speed dial switch.
The four lead wires were spliced into a four-pin connector between the telephone housing and the relay driver, allowing the telephone to be easily disconnected and reconnected to the relay driver. This permitted the telephone to be used manually or removed from the site when needed elsewhere.
The datalogger was programmed to provide a one-second pulse to the control terminals of the relay driver through the two I/O ports. A conditional statement in the datalogger program compares the value of a specified input location to a target value. If the target value is met or exceeded (for example flow > 5 L/m), a subroutine (Appendix A) is called thereby activating the telephone. The telephone calls the phone number of a paging service which activates a tone-only pager.
When the datalogger calls the subroutine (Appendix A) the following steps are executed. First, the subroutine configured each I/O port for output. Second, a one-second pulse is sent to the control terminal of the first relay activating power to the telephone. Third, an eight-second delay allows for a cellular carrier to be obtained. Fourth, a one-second pulse is sent to the control terminal of the second relay activating the speed dial. Fifth, a 30-second time delay allows the call to reach the paging service. Then, a one-second pulse is sent to the control terminal of the first relay, deactivating power to the telephone. Then the program exits the subroutine.
We have used this system at a remote hydrologic research site for over one year and it has proved to be a reliable and valuable tool. The cellular telephone was free with the purchase of twelve months of cellular service. The cost for connect time was $0.30 min -1. Each call to the pager lasted about 40 seconds.
Without the cellular phone system we would have had to visit the site every time we thought it had rained enough at the field site to activate our automatic sampler. Each trip to the site cost approximately $20 in vehicle charges, in addition to the time involved. The cost of the phone charges was easily covered by money saved in travel costs.
During the early portion of the study we had the datalogger call the paging service at a set time each day to confirm that the equipment was functioning. This was in addition to the calling for an increase in water flow in the drainage tile and activation of the automatic sampler. Calls for water flow in the drainage tile were programmed to be sent at 10 minutes past the hour every hour until some one arrived at the site and reset the datalogger program. The time limitation was to prevent us from responding to wrong numbers, when the number of the pager was dialed accidently by some person. The repetition of calls was to guard against missed calls if a cellular connection was not made within the 30 seconds allowed in the datalogger's subroutine.
This system offers a variety of possible uses in a remote site. Any data acquisition activity by the datalogger can be used to initiate a telephone call. Multiple parameters can be programmed to activate the telephone either independently or when a sequence of conditions occur. In addition to monitoring for an increase in flow rate or a drop in temperature, for example, the power supply for the datalogger or other equipment could be monitored. A drop below a specified voltage output would initiate a call at a specific time of day, informing the researchers that the batteries need to be changed. Calls triggered by one set of conditions could be distinguished from another by programming a unique time that calls for each set of conditions would be made.
It is important to realize that modification to a cellular telephone may negate any manufacturer warranties.
We have used this system for over a year without any failures. The number of trips to our research site was reduced without a loss of data, saving both time and money.
Programming example using a Campbell Scientific CR10 datalogger for activation of a cellular phone.
Table 1 program