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Interfacing
The following are the interface connections for the WXTrak, which are needed before operation.
Radio – J1
Female DB-9 connector J1 is used to interface WXTrak to a radio transceiver. It is compatible with the radio connector on
Kantronics TNC, such as the KPC-3. Connect AUDIO OUT (J1 pin 1) to the radio’s mic input. If the transmitter transmits
when the microphone input is grounded (most handheld (HT) radios do, except the Kenwood brand), resistor R8 must be
installed, but PTT OUT (J1 pin 3) will not need to be connected to the transmitter. For all other transmitters, PTT OUT (pin
3) will be needed, and should be connected to the transmitter’s PTT input. PTT OUT is grounded when the transmitter is to
be keyed. To prevent transmissions over other stations, connect the receiver’s squelched audio out (earphone) jack to the
AUDIO IN (pin 5). Also connect J1 GROUND (pin 6) to the radio’s ground. Note: WXTrak cannot decode the incoming
packet data. Instead, it just watches for audio energy (voice, data, or static) to hold off transmitting over other stations.
Refer to the transceiver’s manual for more information, and look for a section on installing a terminal-node controller (TNC)
for packet operation, as WXTrak is interfaced in a similar manner. J1 can also be used to supply or receive WXTrak’s
power, via pin 7 and pin 6.
Serial – J2
WXTrak must be connected to a computer for configuration of call sign and other operating parameters, and then
connected to a compatible weather station to receive weather data. The male DB-9 J2 serial connector is used for this
purpose. J2 pin 3 is used to transfer serial data from the WXTrak to the computer. J2 pin 2 is used to transfer serial data
from the computer or weather station to the WXTrak. J2 pin 5 is serial ground. Both a gender-changer (female-to-female)
AND a null-modem adapter will be needed to interface the computer to WXTrak. A null-modem adapter swaps pins 2 and
3, and connects pin 5. Use a DB-9 serial extension cable if it is difficult to connect the gender-changer, null-modem
adapter, and WXTrak directly to the computer 9-pin serial port. Due to the TTL voltage levels used, some laptop
computers may not be able to communicate with the WXTrak.
If using a weather station cable that plugs directly into a computer serial port, it can be plugged directly into WXTrak’s J2
serial connector. If using a RadioShack WX-200 or Oregon Scientific WM-918, be sure to note the special serial
requirements below. If the station does not connect directly into a computer’s serial port, an interface will need to be built.
The weather station should have a female DB-9 with serial data out wired to pin 2, and ground to pin 5. Weather station
serial input is not used. J2 can also be used to supply or receive WXTrak’s power. If this is desired, short J7 on the back
of the PCB by dropping a bead of solder across the two square pads. After this, J2 pin 4 will be connected to J3 and J1
pin 7.
Note for interfacing to a Radio Shack WX-200 or an Oregon Scientific WM-918:
These weather stations have special
circuitry in their serial sections that use the incoming serial voltage to drive the outgoing serial line. If the station’s
incoming serial is not hooked to a true RS-232 signal, the serial output will be disabled. Since WXTrak does not output a
true RS-232 level, this is a problem. To overcome this problem, a negative voltage (-7 to –15 volts) needs to be sent to
the weather station’s serial input pin, DB-9 pin 3. This can be done in a few different ways.
•
A 9 - 12 battery can be wired to the stations serial port. Wire the negative battery terminal to pin 3, and the
positive to the serial ground, pin 5. Make sure this battery does not come in contact with any other circuitry.
•
A 9 – 12 volt DC wall-wart can be used to provide the negative voltage. Wire the negative side of the wall-wart to
the weather station serial DB-9 pin 3, and the positive side to the serial ground, pin 5. Make sure this wall-wart
does not come in contact with any other circuitry.
•
A MAX232 or similar level converter can be wired to send the negative voltage to the weather staion.
Note: The corresponding pin on the WXTrak (J2 pin 3) should not be connected to the weather station or to this negative
voltage.
Note for interfacing to a Peet Brothers weather stations:
Some users have found that some Peet Bros weather
stations will not output serial data when connected to a WXTrak. This can be corrected by placing a 4.7K resistor between
serial pins 2 & 3.
Power – J3 (also J1 and J2)
WXTrak should be powered with 7-35 volts DC. Power can be applied via J1, J2, or J3. J1 is the most common way to
power the WXTrak. To use J1, connect pin 7 to positive voltage and pin 6 to ground. To use J2, connect pin 4 to positive
voltage and pin 5 to ground. Also, short J7 on the back of the PCB by dropping a bead of solder across the two square
pads. To use J3, apply positive voltage to the plus (+) hole, nearest the LEDs, and ground to the minus (-) hole. Only one
of the three jacks J1, J2, and J3 should be used to supply power to the WXTrak. If power is applied via J2 or J3, the
same power will be available on J1 to power a radio. If power is supplied via J1 or J3, the same power can be retrieved via
