Campbell Siemens TC35T GSM User manual

Siemens TC35T GSM
Digital Transceiver
Instructions for Use
With Campbell Scientific
Dataloggers
Issued 11.12.03
Copyright 2003 Campbell Scientific Ltd.

Guarantee
This equipment is guaranteed against defects in materials and
workmanship. This guarantee applies for twelve months from date of
delivery. We will repair or replace products which prove to be defective
during the guarantee period provided they are returned to us prepaid. The
guarantee will not apply to:
•Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific
•Batteries
•Any product which has been subjected to misuse, neglect, acts of God
or damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs
incurred in removing and/or reinstalling equipment. This guarantee and the
Company’s obligation thereunder is in lieu of all other guarantees,
expressed or implied, including those of suitability and fitness for a
particular purpose. Campbell Scientific is not liable for consequential
damage.
Please inform us before returning equipment and obtain a Repair
Reference Number whether the repair is under guarantee or not. Please
state the faults as clearly as possible, and if the product is out of the
guarantee period it should be accompanied by a purchase order.
Quotations for repairs can be given on request.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package.
Note that goods sent air freight are subject to Customs clearance fees
which Campbell Scientific will charge to customers. In many cases, these
charges are greater than the cost of the repair.
Campbell Scientific Ltd,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
Contents
1. Introduction.......................................................................1
1.1 Using GSM Networks for Data Transfer........................................................... 1
1.2 Network Coverage ............................................................................................ 2
1.3 Call Charges...................................................................................................... 3
2. Initial TC35T Setup ...........................................................3
3. Connection to a Datalogger .............................................4
3.1 SC932C Interface.............................................................................................. 4
3.2 SC932 Interface ................................................................................................ 5
3.3 SC32A Interface................................................................................................ 5
4. Power Supply....................................................................6
5. Antenna – General Notes ................................................. 6
5.1 Antenna Supplied by Campbell Scientific......................................................... 7
6. Configuring the TC35T for use with a Datalogger.......... 9
6.1 Setup ................................................................................................................. 9
6.2 Configuration for the GSM Network .............................................................. 10
6.3 Base Station .................................................................................................... 10
6.3.1 Configuring a Desk-Top Modem as a Base Station .............................. 11
6.3.2 Configuring the TC35T as a Base Station using PC208W.................... 11
6.3.3 Extending the Default Time-Outs.......................................................... 11
6.4 Ending a Call................................................................................................... 12
7. Datalogger Programming Hints ..................................... 14
7.1 Controlling the Power Consumption of the TC35T ........................................ 14
7.1.1 CR10X Program Example .................................................................. 14
7.2 Preventing TC35T Connection Problems ....................................................... 16
8. Fault Finding ................................................................... 16
8.1 General............................................................................................................ 16
8.2 The Base Station Fails to Get a Response from the Datalogger...................... 17
8.3 I get Errors when using the TC35T with Storage Modules............................. 18
Appendix A. Using the TC35T with the PIN Security
Feature Enabled........................................... A-1
A.1 Introduction...................................................................................................... 1
A.2 CR10X Program Example................................................................................ 1
Appendix B. Using the TC35T with the CR23X or CR5000
Dataloggers ................................................ B-1
B.1 Connections...................................................................................................... 1

ii
Appendix C. Details of Useful Configuration commands
for the TC35T ............................................C-1
C.1 Signal Quality Checks .......................................................................................1
C.2 Network Registration Checks ...........................................................................2
C.3 PIN configuration .............................................................................................4
Appendix D. Using the TC35T with Storage Modules .... D-1
D.1 Introduction.......................................................................................................1
D.2 The Problem Explained.....................................................................................1
D.3 Solutions ...........................................................................................................1
Figures
1. Connection of SC932C to TC35T .......................................................................4
2. Connecting the TC35T to a Datalogger ...............................................................5
3. Connection of SC32A to TC35T .........................................................................5
4. Antenna Supplied by Campbell Scientific ...........................................................8
Tables
1. TC35T Power Supply Connections......................................................................6

1
Use of the Siemens TC35T GSM Digital
Transceiver with Campbell Scientific
Dataloggers
This manual provides the technical information needed to use the Siemens TC35T module
with Campbell Scientific dataloggers. More comprehensive technical details of the unit can
be found in the Siemens TC35T hardware and software manuals. These manuals are not
supplied by Campbell Scientific with each TC35T as standard, but are available for
download (in Adobe Acrobat format) from Siemens Web Site (www.siemens.com/wm).
.
1. Introduction
The Siemens TC35T is a module designed to allow transfer of data across a GSM
(Global System for Mobile communications) digital cellular phone network. The
TC35T is a GSM digital transceiver; it can be thought of as a GSM ‘phone’
module without a handset, but which has an extra interface to allow data devices to
be connected. It has the following features:
•Standard RS232 serial port
•Relatively low power consumption
•Wide operating temperature range (-20°C to +55°C)
•Can be used to collect data from a datalogger at a similar speed to a land-
based 9600 baud modem in good reception areas
•Closely emulates a standard ‘Hayes style’ telephone modem; suitable for
situations where the datalogger instigates a call back to a base station, e.g. for
alarm purposes
The dimensions of the TC35T module are 65x74x33mm.
1.1 Using GSM Networks for Data Transfer
GSM networks are based on international standards and are widespread throughout
the world – see the web site www.gsm.org. Theoretically a GSM phone can be
used anywhere in the world if it is within range of a GSM network of the same
standard. For voice communications this theory almost works in practice, except
that many airtime providers (the company you pay for use of the phone) limit the
RS232 Serial Port
Male FME Antenna connector
Power connector

Siemens TC35T GSM Digital Transceiver
2
geographical range of most phones, and some do not have agreements with distant
providers.
For data transmission, most networks support the SMS (Short Message System),
which is not very practical for collecting large volumes of data, but can be useful
for sending alarm messages – see Technical Note 33 for more details of using
SMS. Larger networks support connections where an open data connection is
formed through the network. If this is supported, you may choose to connect to a
GSM data-phone either via a landline modem (landline to GSM) or by using a
second GSM phone in your office (GSM to GSM).
Before considering the use of the TC35T in your application, check with your
local GSM network company that they support the use of the Siemens TC35T for
the ‘non-transparent’ mode of data transmission, at 9600 baud. Check also that
they provide suitable routes to allow you to communicate with it, such as access
via land-line modems.
The current design of the TC35T will operate on GSM900 (900 MHz) or
GSM1800 (1800 MHz) networks. Whenever possible a GSM900 network should
be used as 1800 MHz networks (which includes the Orange and One to One
networks in the UK) are designed with smaller cells, and so phones (including the
TC35T) transmit at lower power outputs. All GSM1800 phones therefore have a
shorter range, which can cause more problems in areas of dubious signal coverage.
1.2 Network Coverage
One of the main advantages of using a cellphone network is being able to set up a
communications link to a datalogger virtually anywhere without installing land or
telephone lines. However, this only applies if your installation site is covered by a
suitable GSM network.
Within the UK the coverage of GSM networks is now better than the older analogue
networks. However, coverage in remote areas can still be quite poor and is not likely
to improve, as it offers little commercial advantage to the network companies.
Unless coverage is known to be good at the proposed site, we strongly recommended
that you actually test the coverage using a standard GSM handset (on the same
network as the TC35T is to be used) to measure the exact signal strength.
Even areas shown as having good coverage on network maps can have
‘holes’ due to local interference or other technical reasons, and so site
testing is recommended.
In areas of normal signal strength the TC35T can be used with a small, low cost
antenna. However, if the signal strength is marginal it may be possible to improve
reception using a raised and/or a higher gain antenna. Poor quality reception will
normally lead to breaks in communication or result in the PC software having to
make multiple requests to ensure uncorrupted data is collected. This will not
usually lead to data loss or corruption, but may result in longer calls and thus
higher call charges.
The network maintainer will be able to offer advice on coverage problems.
Campbell Scientific can also offer further advice on suitable antennae to suit the
application.
NOTE

Using with Campbell Scientific Dataloggers
3
1.3 Call Charges
Call charges on cellular-based phones are usually much higher than landline based
systems and can therefore be quite high for a long-term data collection campaign.
Careful choice of the tariffs available can result in a considerable reduction in the
total bill. Obviously the tariff chosen should allow use of the phone for data
transmission. Some very low cost packages are limited to voice only, but some
companies offer cheap data-only tariffs as well. Limiting calls to off-peak and
weekend periods can also result in major cost savings.
One major factor which can determine call costs is the method used to connect to
the remote TC35T. If you call the TC35T from a landline phone modem, you will
normally pay your landline phone company the same (high) cost as calling a voice
cellphone. This is independent of your agreement with the cellphone airtime
provider. In many cases it may be cheaper to buy an extra TC35T for your base
station, thus avoiding the use of the land-based phone line altogether. This could
also enable you to benefit from the special tariffs for data-only transmission
provided by the airtime companies. Also, the set-up time from TC35T to TC35T is
usually much lower and the overall call will thus be shorter and cheaper.
If you cannot use a base station TC35T, cheaper calls may also be possible by
programming the datalogger to call back to the land-line phone base station, as the
special airtime rates will normally apply to such calls too.
Where many calls have to be made in quick succession ISDN digital landlines can
be used with a digital terminal adaptor in the calling PC. If correctly supported and
set-up for the phone account by the network operator, the connection time can be
reduced to one or two seconds. This is done by setting the system to communicate
in a digital fashion throughout (UDI mode). Please contact Campbell Scientific
Ltd for further advice on this matter.
2. Initial TC35T Setup
Before the TC35T can be used or tested, it must be fitted with a ‘SIM’ (Subscriber
Identification Module) which enables it for use on a specific cellular telephone
network in a particular frequency band. For some networks, e.g. BT Cellnet in the
U.K, you need to specify the mode of data transfer. If this is required, request it to
work in ‘non-transparent mode’ at 9600 baud. This is the default setting for most
networks. Your airtime provider will normally supply you with an extra phone
number for the SIM specifically for data use.
The TC35T does not support the older transparent mode of
communication.
If possible, ensure that the SIM is configured so that it does not require a Personal
Identification Number (PIN) security code to be entered after the module is
powered up. The PIN can most easily be disabled by inserting it into a separate,
hand-held standard GSM phone and following the instructions contained in the
phone manual. If a separate phone is not available, please contact Campbell
Scientific for details of how to disable the PIN code for use with the TC35T. If this
is not possible, or if your airtime provider only allows operation with a PIN
enabled, please refer to Appendix A.
NOTE

Siemens TC35T GSM Digital Transceiver
4
Many SIM suppliers send the SIM with the PIN enabled and set to a
default PIN number. Check the documentation that came with your SIM.
3. Connection to a Datalogger
To enable normal operation of all Campbell Scientific peripherals which might
share the 9-way serial I/O port on the datalogger (e.g. Storage Modules), it is
necessary to use an interface between the datalogger and the TC35T. A number of
different interfaces can be used. Figure 2 shows a diagram of the recommended
interface and connections between a datalogger and the TC35T.
If using a CR23X or CR5000 datalogger, a simpler alternative connection is
possible using the RS232 port, if this is available. Please refer to Appendix B for
further details.
If you want to use the TC35T to communicate with storage modules
connected to the datalogger, please see Appendix D for advice on
possible problems you might encounter.
3.1 SC932C Interface
This is the preferred interface because:
•If the TC35T is programmed to respond to the DTR line state (see
‘Configuration for the GSM Network’, in Section 6, below), it allows the
datalogger to force the TC35T into an off-line state, if required.
•The SC932C only consumes <0.5mA when there is no communications and 10-
12mA when communications are active, from the datalogger 5V output. (This
is in addition to the power consumed by the TC35T which is approximately
20mA quiescent and 100-200 mA online.)
Connection to the TC35T is as follows:
25-Way D
Pin No.
9-Way D
Pin No.
23
3
75
20 4
SC932C TC35T Module
2
Figure 1 Connection of SC932C to TC35T
A commercial 9-25 way modem cable can be used in place of the
cable design shown in Figure 1. However, such a cable will have
extra connections that will increase the quiescent current drain of the
SC932(C) by 1 mA.
NOTE
NOTE
NOTE
Female Male

Using with Campbell Scientific Dataloggers
5
3.2 SC932 Interface
The original SC932 can also be used with the TC35T module, and can be used
with the cable described above. The SC932 can be set to its lowest power mode
(see the SC932 manual for details of the jumper settings required).
3.3 SC32A Interface
This is not the best interface to use as the SC32A does not support hardware
handshaking, and therefore the datalogger cannot force the TC35T to shut down.
The SC32A is only included here for reference because many users may already
have one. Connection is as shown in Figure 3.
Fit the SC32A’s internal jumper so that synchronous data (such as data intended
for a Storage Module) will not be sent to the TC35T. Configure the TC35T (see
‘Configuration for the GSM Network’, in Section 6, below) to set the DSR line
high all of the time. In this state the TC35T, when the power is turned on, will
consume its quiescent current plus around 2-3mA to power the SC32A.
25-Way D
Pin No.
9-Way D
Pin No.
22
3
75
20 6
SC32A TC35T Module
3
Figure 3 Connection of SC32A to TC35T
Male Male
Connect to 9-pin
‘CSI’ socket on
datalogger
Blue SC12 ribbon cable
SC932C Interface
9-pin 25-pin
TC35T Cable (SC932C to 9-pin)
(see Figure 1, above)
TC35
Figure 2 Connecting the TC35T to a Datalogger
Diagram Not to Scale
Connect to 9-pin socket
on TC35T

Siemens TC35T GSM Digital Transceiver
6
4. Power Supply
The TC35T module requires a power supply capable of supplying 8-30V DC, at an
average current of up to 200mA, with short peak currents of 2A. Siemens
recommend that a 1.25A, ‘fast blow’, fuse is inserted in the positive rail of the
supply, to minimise damage in the event of a failure. Campbell Scientific fit such a
fuse in an in-line fuse carrier. Additionally, Campbell Scientific power supplies
include a slow response solid-state automatic resetting fuse.
If the TC35T is to be powered from the same supply as the datalogger, ensure that
the power connections for the TC35T are made as close as possible to the battery
outputs. This will prevent the TC35T causing voltage drops and noise on the
supply to the datalogger.
Although the TC35T has an ‘Ignition Sense’ line, this line does not have the same
function as was provided in earlier Siemens models, and cannot be used to turn the
unit on and off. For units supplied by Campbell Scientific, this line is tied to the
positive supply and a power switch is incorporated in the cable to allow the
datalogger to turn the unit on and off via a wire connected to one of its control
ports. During testing or configuration it may be necessary to move this wire to the
12V supply to ensure that the module is powered continuously.
The TC35T may not power up correctly if its power cable is
removed and re-inserted while 12V power is applied. Always
switch off the power supply before unplugging or inserting the
cable.
Table 1 TC35T Power Supply Connections
TC35T Cable Colour Connection
Red (positive supply) +12V
Black (negative supply) G
Yellow (power control) Control Port (or +12V for testing)
N.B. These colours and connections only apply to the cable supplied by
Campbell Scientific Ltd.
If you are not using the Campbell Scientific power lead, the 12V power supply can
be controlled using a solid-state power relay (such as the Campbell Scientific
PSW12) or you can use the power switch fitted to recent CR10X or CR23X
dataloggers.
Only the power switch in CR10X wiring panels fitted with green
terminal blocks is suitable.
5. Antenna – General Notes
When selecting an antenna, please note the following points:
•make sure the antenna used covers the frequency you intend to use the TC35T
on, i.e. does the antenna cover 900 or 1800 MHz, or both (dual band).
•Low cost, ¼- or ½-wave antennae are adequate for most applications where
signal coverage is good. It is important to realise that most cheap antennae
designed for vehicle mounting require a flat, metal sheet to form a ground
plane at the base of the antenna to achieve the specified gain figure and to
CAUTION
NOTE

Using with Campbell Scientific Dataloggers
7
ensure proper impedance matching. As an approximate rule the ground plane
should have a radius equal to or greater than the height of the radiator.
•Slightly higher priced co-linear, ‘marine’-grade antennae do not require such a
ground plane and can be more easily pole or cross-arm mounted.
•In areas of poor signal coverage a directional, high-gain ‘Yagi’ antenna can be
considered, but this requires knowledge of where the cell base stations are
situated in order to enable proper alignment.
•Raising the antenna is often the most effective way of getting better signal
reception. However, if long cables are required to achieve this, use low-loss
extension cables that do not have the significant signal loss of cheaper cables.
Long cables are a particular problem when operating at 1800MHz.
•Like most cellular-based systems, the TC35T varies its transmitter power to
ensure good communications with the remote cell station. Using a cheaper,
low-gain, antenna may result in a significant increase in power consumption in
areas of poor signal coverage.
•If the antenna is placed near the top of a mast it may be vulnerable to lightning
damage. If lightning is common at the installation site, additional lightning
protection may be required to protect the TC35T – please contact Campbell
Scientific for further advice.
Using an antenna that is installed incorrectly, or with faulty
wiring, can lead to premature failure of the transmitter output
of the TC35T.
Install the antenna so that the radiator is positioned away from other vertical metal
structures. It should also be at a distance from any sensors so that it does not either
physically or electrically interfere with the sensor readings. If the TC35T is
connected to a PC (see below) it is possible to check the received signal strength
using the AT+CSQ command (see Appendix C or the TC35T manual for further
details). This can be used to find the optimum antenna position. You should aim to
get the highest signal strength (as close to 31) as possible. For reasonable
communications you need a minimum level of approximately 10 when operating in
non-transparent mode. Be sure that the module is configured to talk only to the
network operator you intend to use when doing this (see the AT+COPS
command).
Many antennae have bodies that are connected to the coaxial
cable screen. It is therefore essential to ensure the correct
polarity is maintained through the cabling system to avoid the
possibility of shorting the transmitter output of the TC35T to
the power supply ground via the lightning protection cables
and mounting structure.
5.1 Antenna Supplied by Campbell Scientific
Campbell Scientific can supply various antennas, if required, including a ‘low-
cost’ antenna (see Figure 4, below).
In areas of high signal strength, the low-cost antenna will be suitable for almost all
applications, either at 900 or 1800 MHz. The antenna, as supplied ‘off the shelf’,
is fitted with a connector which will directly fit the TC35T transceiver aerial
socket. When the antenna is supplied as part of a weather station or other complete
installation, Campbell Scientific may replace the original connector with a
compatible connector before the system is tested.
CAUTION
CAUTION

Siemens TC35T GSM Digital Transceiver
8
In a field installation it is recommended that the cable length between the antenna
and the transceiver is kept as short as possible to reduce the signal loss in the cable,
although, as mentioned above, it is often more advantageous to mount the antenna
higher. In some applications the cable will need to be shortened, and so the new
connector can be installed onto the cable at this time by cutting off the surplus
cable, together with the original connector, and fitting the new connector. Ensure
that all connections are well made, and the connector is secured using a crimping
tool or pliers. The connector is only suitable for use in dry environments and so
must be protected from direct exposure to water and precipitation.
Figure 4 ‘Low-cost’ dual-band antenna supplied by Campbell Scientific
The antenna is supplied with a special mounting bracket, as shown, allowing it to
be fitted to 25-27mm diameter horizontal tubing. Alternatively it can be screwed to
a suitable flat surface. The dipole design of the antenna means that no ground
plane is required, thus allowing more flexibility in mounting. Avoid mounting the
antenna close to other vertical metal structures or on flat metal surfaces. Higher
gain YAGI style antennas are available from Campbell Scientific to special order.
160mm
approx.
120mm
approx.
Mounting bracket for
25-27mm diameter
tubing

Using with Campbell Scientific Dataloggers
9
6. Configuring the TC35T for use with a Datalogger
Before you install the TC35T, you must configure it and store the settings in its
non-volatile memory so that when power is applied it works in the correct way
with the datalogger.
If your TC35T is supplied in an enclosure with a datalogger and
other peripherals, it will normally be pre-configured with the correct
baud rate and with the default settings. Normally no further
configuration is required, unless you wish to change the error
correction mode.
6.1 Setup
To enable configuration:
1. Connect the TC35T to a PC. The serial port on the TC35T allows a direct
connection to a PC ‘AT’ (9-way) style serial port with a cable that has a pin to
pin connection system. A Campbell Scientific SC12 cable can be used if no
other cable is available.
2. Connect the TC35T to a suitable power supply, ensuring that the power control
line is held high to force the TC35T to remain switched on permanently during
configuration.
3. Select a suitable terminal emulation package (e.g. HyperTerminal, included
with Microsoft Windows 95/98) to communicate with the TC35T in order to
configure it. Campbell Scientific’s Term or GT programs can also be used,
with the datalogger type set to NONE. In the first instance set the terminal
emulation package to communicate at 9600 baud, 8 bits, 1 stop bit, 1 start bit
and no parity. The terminal type emulation is not important
4. To check communications with the TC35T type AT&F and press ENTER. The
TC35T should respond on the following line with OK. This resets the TC35T to
the default settings. Please refer to the TC35T manual for full details of the
commands. The TC35T uses a similar command set to a ‘Hayes-compatible’
telephone modem, with the addition of some extra commands for the
configuration of the GSM module functions.
5. The default baud rate setting for the TC35T is automatic baud rate detection.
You need to set this to fixed operation at 9600 baud for use with Campbell
Scientific dataloggers. To change the setting type AT+IPR=9600. This will
change the communications speed and write the setting to non-volatile
memory. If someone has set another fixed baud rate you may have to
experiment in changing the terminal emulation baud rate until you get the
TC35T to respond, allowing you change and fix the rate at 9600 baud. Please
remember that some terminal emulators, such as HyperTerminal require you to
click on the disconnect button and then reconnect before the changes to
communications baud rate come into effect.
If you get the response ‘ERROR’ or ‘4’ after entering the
above AT commands, please ensure that the terminal
software is set up to communicate via the COM port to which
the TC35T is connected, and not with any internal modem
which may be fitted in the computer.
NOTE
CAUTION

Siemens TC35T GSM Digital Transceiver
10
6.2 Configuration for the GSM Network
The TC35T must be configured to work on the particular network for which its
SIM is valid. These settings will probably have been pre-set by the supplier of
your SIM. If not, refer to details in Appendix C or the Siemens TC35T operator’s
manual with reference to the AT+CREG and AT+COPS commands.
A summary of the configuration procedure is:
1. Make sure the modem has been fully reset and then configured to run at 9600
baud as detailed above.
2. Issue the required commands (see below) either individually or in combination.
3. Issue the final AT&W command to store the set-up in non-volatile memory.
The following commands are required to change the settings from the factory
defaults (please refer to the Siemens TC35T manuals for full details). Enter the
command and then press the return key. Wait for a response before proceeding
with the next command.
AT&F Reset to factory default settings.
ATX0 Basic connect messages only
(AT&S0 Force DSR high - required only for use with the SC32A or
RAD modems.)
(AT&D0 Ignore DTR. This is only required for, and so should only be
used with, a CR200 series datalogger used with a null modem
cable or older dataloggers such as the CR7 and 21X.)
ATS0=1 Set the TC35T to auto-answer incoming calls
ATV0 Numeric result codes – the TC35T will not respond with ‘OK’
to this or following commands; instead it returns ‘0’ (zero) at
the start of the current line.
AT&W Saves all of the above settings in non-volatile memory.
To validate all settings are correct, issue the AT&V command to display all of the
non-GSM settings on the screen. Make sure the settings are all shown in ‘Active
Profile’.
If you get the response ‘ERROR’ or ‘4’ after entering the
above AT commands, please ensure that the terminal
software is set up to communicate via the COM port to which
the TC35T is connected, and not with any internal modem
which may be fitted in the computer.
Also ensure that the TC35T has a valid SIM installed with the
PIN security function unlocked or disabled.
6.3 Base Station
Either a standard desktop modem or the TC35T itself can be configured as a base
station. Details are given in the following sections.
6.3.1 Configuring a Desk-Top Modem as a Base Station
The modem to be used as a base station should first be selected, either by editing
your MODEM.INI file if using the DOS version of the software or by selecting the
correct modem setting in PC208W. With PC208W version 3 onwards, the "default
modem" will work with most modern modems. In some cases, though, particularly
CAUTION

Using with Campbell Scientific Dataloggers
11
with Nokia GSM phones, the modem setting may need to have the extra codes
"X0" added to the initialisation string to ensure correct operation.
The baud rate for connection should be set to 9600. Any existing initialisation
strings specified in MODEM.INI or in PC208W’s modem set-up will still apply,
but it may be necessary to add additional settings to limit the connection protocols.
This is because, in practice, some of the newer high-speed modems have been
found to attempt to negotiate connections that cause the GSM network modem to
immediately drop the line. For connection on a GSM network the modem only
needs to establish a 9600 baud, V32 connection. For many recent Hayes
compatible modems this is set by adding ‘S110=0’ or the command +MS=9 at the
end of any existing initialisation string. In addition, some networks will reject calls
if data compression is enabled. These functions are controlled by the initialisation
strings sent to the modem.
For LoggerNet Version 2.0, providing the modem is installed under Windows
correctly, it should be simplest to use the TAPI interface option and select the
modem from the TAPI line option that shows the installed modems.
While Campbell Scientific Ltd may be able to give some advice as
to the best settings to use for common modems, the connection of
the landline modem to a cellular network is specific to the cellular
network being used. Problems establishing the connection are often
not related to the fact that a TC35T or datalogger are connected at
the remote end of the connection, but are caused by compatibility
issues of the PC modem with the network. Please also contact your
cellular network support team for advice on any problems that you
might encounter.
6.3.2 Configuring the TC35T as a Base Station using PC208W
The TC35T should first be set up as if it were to be used with a datalogger (see
section 6.1 above). Although some older versions of software may work, we
recommend that PC208W Version 3, Loggernet 2.0 or later versions are used. The
instructions below apply only to such software.
To use the TC35T, after the initial set-up, connect the modem to the PC then run
PC208W. Choose the ‘Setup’ screen and add a phone modem to a COM port. Select
the modem type ‘Default Modem’ and select ‘Edit Modem Strings’. Overtype the
name of the modem to make it read ‘TC35T’. The only other setting you need to add
is a "+CBST=n,0,1" command to the end of the ‘Modem Initialisation’ string, where
n is network specific, e.g. the previously set value of 7 will work but some networks
recommend 71 to force a digital connection which can reduce the connection time.
See the PC208W manual for further advice — Appendix A will give specific
advice on using and adding modems, initialisation strings, etc.
6.3.3 Extending the Default Time-Outs
When using either a landline base modem or a TC35T as the base, it is sometimes
necessary to add “S7=45” to the end of the modem initialisation string. This setting
extends the time both the PC and the base modem will wait before timing out an
attempted connection to a remote modem to 45 seconds. This setting may also be
required for normal desktop base modems. The default setting for the PC software
is 30 seconds, which can be a little short if the GSM network is busy. Normally you
are allowed to increase this setting up to 60 (seconds) if a call is seen to take such a
long time to connect. Setting too long a delay may, however, slow down the retry
sequence in the event of a failed connection.
NOTE

Siemens TC35T GSM Digital Transceiver
12
Campbell Scientific communications software includes other time-outs which are
used to check for hung communications links. These are set to be quite short for
land-based modems, as the response to any command sent from the PC should be
almost instantaneous. A link to a remote TC35T normally passes through several
nodes of a digital data network, all of which can add delays. Usually these delays
are less than one second and so have no effect on the communications process.
However, on a long distance call or busy network, the built in time-out delay for
the PC software may need to be extended.
Using PC208W, a station-specific delay can be added by increasing the time in the
‘Extra response time’ box shown on the datalogger hardware set-up screen. This
delay is entered in milliseconds. PC208W (version 3 or later) has a default extra-
response delay of 2000 milliseconds, which is adequate for use with the TC35T in
most cases. (Older versions of the support software have a default setting of zero
milliseconds and this value will need to be increased, but it is strongly
recommended that you use PC208W version 3 or later.) On busy networks, or with
poor communication links, a value of 3000 or even 4000 may be required, to allow
the error correction process to function.
Where a TC35T is used as the base station modem, it is advisable to increase these
delays even more by perhaps another 1000-2000 milliseconds, if communications
are proving to be unreliable.
Entering too large a delay can slow down the entire communications
process, and so an optimal value should be determined by trial and
error.
If using Loggernet 2.0 you should be aware that extra response
delays are entered in seconds rather than milliseconds.
6.4 Ending a Call
If the SC932 or SC932C interface is being used, the communications session is
ended when either:
a) the datalogger is told to finish the communications session by the PC
OR
b) one of the datalogger time-outs causes the call to finish
One of the two conditions described above will cause the datalogger to lower the
DTR line and force the modem off-line. Some GSM networks are unable to signal
this change of state back to the calling modem, in which case the calling modem
will often stay on-line and sometimes receive what appears to be random data from
the network.
Usually the PC software will detect this as an error and force the calling modem
off-line. Current versions of PC208W will ensure the modem is forced off-line as
quickly as possible in this event; older software may remain on-line for an extra
one or two minutes and so could incur extra phone charges.
NOTE

Using with Campbell Scientific Dataloggers
13
7. Datalogger Programming Hints
7.1 Controlling the Power Consumption of the TC35T
The power consumption of the TC35T system is much lower than older analogue
cellphones, being typically 20mA while waiting for calls and <200mA when on-
line. The TC35T, as supplied by Campbell Scientific, has a built-in power switch
which allows the datalogger to turn off the TC35T. However, the TC35T will not
answer any incoming calls when in this state.
The first thing to consider when designing the power supply for your TC35T
system is the possibility of only switching on the TC35T for, say, one hour per
day, during which time a base station can be synchronised to collect data. The
lowest overall power consumption can be obtained by making the datalogger turn
the power on only when it makes outgoing calls. However, this would prevent you
calling the datalogger at will from a base station to check its status or to load a new
program.
Once the total time per day that the datalogger will be turned on in its different
power states is determined, a daily power consumption can be estimated and the
power supply designed accordingly. For most typical remote applications a
PS12E-LA and a medium-sized solar panel will suffice. Please refer to Technical
Note 12 (Calculating Power Consumption and Solar Panel Size) for further details.
To allow the TC35T to receive calls, program the datalogger to set the relevant
control port high to turn the TC35T on. The TC35T will not answer an incoming
call when the power control line is low. Control is normally done using the
datalogger instruction P92 (If Time) with the command option to set the port high
(after an additional check on the battery status) or low at specific times.
The time for which the TC35T is switched on needs to be long enough to allow an
incoming call to be started, data collection made and the call completed. The
CR10X and later dataloggers allow an extra refinement to this sequence, which
allows the ‘on-time’ to be reduced further. This is because extra options (options
40 and 50) have been added to instruction P91 (If Port/Flag). These options allow
the program to determine if the datalogger is already communicating and on-line
(40) or off-line (50). The program can then be written to turn off the TC35T only
if the datalogger is not communicating. The following sequence could be included
in a program to turn on the TC35T for 5 minutes every hour, but only turn it off if
a call is not in progress.
7.1.1 CR10X Program Example
;TC35T power control example code for the CR10X
;Port 1 is the control port used to switch the TC35T ON/OFF
;Flag 1 is used to indicate the TC35T should be turned off
;when any current call has ended.
;On the hour turn the TC35T on
;IF the battery voltage is good (see text below)
1: If time is (P92)
1: 0000 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 30 Then Do

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;Measure the logger battery voltage
2: Batt Voltage (P10)
1: 1 Loc [ BattV ]
;and if it is > than 11.5 V turn on the TC35T
3: If (X<=>F) (P89)
1: 1 X Loc [ BattV ]
2: 3 >=
3: 11.5 F
4: 41 Set Port 1 High
4: End (P95)
;At 5 past every hour set Flag 1 to indicate to turn off the
;TC35T when any current call is finished.
5: If time is (P92)
1: 5 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 11 Set Flag 1 High
;If Flag 1 is set AND
6: If Flag/Port (P91)
1: 11 Do if Flag 1 is High
2: 30 Then Do
;the datalogger is not communicating (ME off) THEN
7: If Flag/Port (P91)
1: 50 Do if Modem is Off
2: 30 Then Do
;Turn off the power to the TC35T
8: Do (P86)
1: 51 Set Port 1 Low
;and set low flag 1, to allow it to be turned on next time
9: Do (P86)
1: 21 Set Flag 1 Low
10: End (P95)
11: End (P95)
If power is limited and the turn-on time has to be kept very
short, it is critical to ensure that the PC and datalogger clocks
are not allowed to drift apart, otherwise the PC may try to call
when the TC35T is turned off. Clock synchronisation can be
achieved automatically, during data collection. Please refer to
the PC208W manual for details on how to do this.
The TC35T can also be used with instruction P97 (Initiate Telecommunications)
to make an outgoing call, either to return data to a remote computer or in the event
of an alarm. Instruction 97 is normally controlled by a program flag (referred to as
the Interrupt Disable Flag when programming P97) which is set low to make P97
initiate communications and call out. The process of setting this flag is normally
controlled by some program control logic before P97 is executed.
To ensure that the TC35T is powered on for the outgoing call, an extra P91
instruction should be included before P97 to set the power control port high if the
CAUTION