The data logger may be in the radio enclosure, or it may be left separate. In either case the radio power should be from the logger's switched 12 volt supply terminals. Program steps must then be added to control the radio, based on time and on the available battery voltage.
The Put River station has generally been operated using a battery, but without a charging system. While this was sufficient for running the data logger, the radio will increase power use considerably, and it will be necessary to arrange for charging, e.g., by solar panel.
The necessary radio control programming will prevent hourly operation of the radio if the battery voltage drops to a set level, e.g., 12 volts. The radio will still be turned on for 10 minutes at noon, regardless of the voltage.
The CR10X data logger provides controlled power on a terminal marked
SW 12V, and this should connect to the radio's positive lead, with
the 0V lead going to the G terminal.
Adjacent to the SW 12V terminal is a terminal marked SW 12V CTRL.
This is actually an input, and should be connected by a short wire to
an available control port. The logger program can then control radio
power by setting or clearing that control port.
Note that the SW 12V can be manually turned on by moving the SW
12V CTRL wire to a 5V terminal.
The Freewave DGR-115W uses a 10-pin connector and cable to bring power and comms signals out. In some cases this terminates in a DB9F (9 pin, female) connector, and may be directly connected to a Campbell SC932A convertor which in turn connects to the logger.
In some cases, we have terminated the radio cable to an RJ45 jack (with power leads coming out separately), mainly so that longer cable runs could be made without needing to accomodate the size of DB9 connectors. A special connector is required to accept an RJ45 jack and present a DB9F connector for connection to the SC932A (and thence to logger).
Please use care when handling these RJ45 connectors; they have plastic, snap-together housings and can pull apart in a number of alarming ways. With due care they should provide reasonable service (but do constitute a potentially weak link in the system).
See wiring diagram for details.
Campbell data loggers are remarkably low power devices, and work reliably under difficult environmental conditions. The Freewave radio presents a considerable load, e.g., about 60 mA when powered, over 1/2 amp when transmitting (which is of vanishingly brief duration, however), so care must be taken with power supplies.
At WERC, our approach to this problem is to limit the operation of the radios to only a few minutes per hour, and to consider the average load in the sizing of batteries and solar panels. If operated for 3 minutes per hour, the average load of the radio is only about 3 mA, vs 60 mA if operated continuously. This lower power level is on a par with some of the instruments normally connected to the data logger.
The power system requires a storage battery connected to the logger terminals, and in most cases a solar panel for charging the battery, connected using a suitable charge controller.
Remote systems which must operate over the winter may benefit from a large battery bank (e.g.,150 to 250 AH), and also a large solar panel (e.g., 50 W), but we have found that a smaller power system can often suffice. Conditions affecting the charging system should also be considered, e.g., available sunlight, icing, etc.
The Put. River gaging site is only operated during the summer months, so could get by with a small power system. A 10 W solar panel and 20 AH battery would probably be plenty.
The following program is from another site so will require modification for use on the Put R logger. The battery voltage location and the control port are probably the main variables here.
1:P10 ; BATT VOLT
1:13 ; store in location 13
The following instruction defines the control port as an output. It is optional, but if omitted, the control port cannot be forced on (e.g., using keypad commands) until the port is set by the program on the hour.
2:P20 ; PORT SET
1:9999 ; P8=nc, P7=nc, P6=nc, P5=nc
2:9799 ; P4=nc, P3=output, P2=nc, P1=nc
At the top of the hour we clear flag 1 if the voltage is too low, and turn
on the control port (connected to SW 12V CTRL) if the voltage is not too
low:
3:P92 ; IF TIME
1:0 ; is 0 minutes into
2:60 ; 60 minute interval
3:30 ; then DO...
4:P89 ; IF X < = > F
1:13 ; if X from location 13
2:4 ; is <
3:12.2 ; fixed value 12.2
4:21 ; set flag F1 low
5:P89 ; IF X < = > F
1:13 ; if X from location 13
2:3 ; is >=
3:12.1 ; fixed value 12.1
4:43 ; set port C3 high
6:P95 ; END IF-DO
At noon, turn on the radio without regard to the battery voltage:
7:P92 ; IF TIME
1:720 ; is 720 minutes into
2:1440 ; 1440 minute interval
3:43 ; set port C3 high
Only consider turning off the radio if flag 1 is low:
8:P91 ; IF FLAG/PORT
1:21 ; if flag F1 is low
2:30 ; then DO...
9:P92 ; IF TIME
1:5 ; is 5 minutes into
2:60 ; 60 minute interval
3:53 ; set port C3 low
10:P95 ; END IF-DO
These instructions should run every minute. Note that flag F1 is
used to prevent the radio from powering down, but does not cause power
to be applied. The control port, C3 in the example, can be used to
directly control the radio power, e.g., using a keypad or other interface.
To toggle flags or ports, view input locations using mode *6, advance so that a value (any value) is displayed, and use D to view flags, 0 to view ports. With flags or ports displayed, pressing a number will cause that flag/port to toggle; pressing A or B will go back to displaying input locations.
An aside on RS232 terms and use may be in order. The RS232 standard was designed to connect DTE (data terminal equipment, or terminal) devices together using a DCE (data communication equipment, or modem) on each end. The modems could then communicate by whatever means they had, e.g., phone lines, radio signals, acoustical, pigeons, etc. So a standard use of RS232 could be depicted something like this:
DTE---DCE - - (modem-to-modem link) - - DCE---DTE
In order to connect DTE devices directly together it is still necessary for each terminal to think it's connected to a modem, and the null modem cable provides this function:
DTE---(null modem cable)---DTE
Besides using the terms DTE, DCE, null modem, etc., it is alternatively
possible to understand RS232 connections in terms of the wiring. This is
particularly true if the equipment uses only a few of the pins, and this
is true in many (but not all!) cases. Despite the fact that older RS232
connectors have 25 pins, and newer ones 9 pins, only 3 signals are needed
in the simplest systems, namely TD (transmit data), RD (recieve data),
and G (common or ground).
The following table shows the pin numbers for these signals based on the standard 9-pin connector (aka DB9), and depicting a terminal connected to a modem device:
DTE -to- DCE
TD = 3 RD = 3
RD = 2 TD = 2
G = 5 G = 5
There are also a number of control lines available, however, and it must be noted that these sometimes are required, and that a considerable amount of detail may need to be negotiated to make things work in such cases. In this case it is probably better to use standard cables, e.g., straight through and null modem as appropriate, and the DTE and DCE terminology to make sense of things. It should be sufficient (except in special cases) to say that if a device transmits on pin 3 (on a DB9 connector) then it is DTE, and etc.
The serial port on a standard computer, whether desktop or laptop, is DTE, so a straight-through cable can be used here. Note, however, that Palmtop and Palm Pilot handheld computers are DCE on their serial port, and so it is necessary to use a null modem cable to make a working connection in this case.
The Freewave radios operate as modems, or DCE devices, so can connect to a laptop (DTE) using a straight-through cable, or to a Palmtop or other DCE device using a null-modem cable.
The Campbell data loggers use a non-standard wiring arrangement (and voltage levels), and for this reason a convertor device must be used to connect logger to PC, laptop, palmtop, or radio. The SC932A, for instance, allows connecting directly to a DCE device, e.g., a Freewave radio or a Palmtop computer, or to a DTE device if a null-modem cable is also used.