From cbouck01 at twcny.rr.com Sun Aug 29 13:27:52 2004 From: cbouck01 at twcny.rr.com (Chris Bouck) Date: Sun, 29 Aug 2004 09:27:52 -0400 Subject: [htaprs] Has anyone used this Wrist Watch GPS Unit for TH-D7 Message-ID: <000801c48dcb$fcb4c780$6eef3a18@twcny.rr.com> WA8LMF Home Page | Main Ham Radio Page | Main APRS Page | Updated 27 Aug 04 Garmin ForeTrex 201 "Personal Navigator" Wrist GPS This GPS receiver may well be the ultimate accessory for the Kenwood TH-D7 APRS hand-held radio. The TH-D7 has a serial data input jack for transmitting position reports provided by an attached GPS receiver. However most GPS devices are nowhere near as conveniently portable as the Kenwood radio. The Garmin ForeTrex 201 "Personal Navigator" is a miniature GPS receiver that you wear on your wrist like a watch. The device is secured to your wrist with a Velcro strap and is powered by an internal rechargeable lithium-ion battery. Specs in the manual say the battery will power the unit for up to 15 hours. The unit is WAAS-enabled. The area under the GARMIN logo is the built-in patch antenna. It is astonishingly sensitive. I found that it worked quite consistently while walking with my arm by my side, with no special efforts to orient the unit favorably to the sky. It even worked inside the car as long as I wore it on my left hand and kept my left hand on the steering wheel. ( I assume one would have to wear it on the right hand to get the same results in the U.K!) The unit lists for USD $179 but I got mine through an Internet mail-order dealer for $135 In addition to it's own extensive data displays presented on a very legible LCD screen, the unit outputs NMEA 0183 4800 baud 8-N-1 serial data through a 2.5mm stereo minijack. Click here for a page of screen shots of the Foretrex screens. The external power and serial port are contact pads on the back of the Fortrex. A separate "cradle" snaps onto the back of the unit, mates with the pads, and presents a 2.5mm stereo mini-jack for data, and a 1.7mm micro-miniature coax power jack for 5 VDC power input. The cradle is intended to be snapped onto the unit for charging while you are not wearing it, However, the ForeTrex is perfectly wearable with the cradle installed. It adds about 1/4-inch height to the 201. The unit comes with a 2.5mm-stereo-miniplug-to-DB9-female connector cable to connect the ForeTrex to a PC. This cable has identical pinout to the one used to program a TH-D7 or VC-H1 from a PC. To use the unit with a Kenwood TH-D7, acquire a 2.5mm-to-2.5mm stereo patch cord. Cut the cable in the center and cross the two hot conductors conductors (TXD and RXD). Plug one end into the ForeTrex and the other into the GPS port of the TH-D7. Set the TH-D7 APRS menu to use a GPS. Navigate to the ForeTrex setup menu and set the external port to NMEA (it defaults to Garmin proprietary format). The baud rate is fixed at 4800. When you press the "POS" button on the TH-D7, you should see the same coordinates, truncated by one decimal place, as the ForeTrex display. With ForeTrex firmware versions before 2.3, the device reverts to Garmin format every time the unit is switched off. With the firmware upgraded to 2.3 or higher (a self-installing upgrade that runs in Windows is downloadable from the Garmin website), the unit remembers the NMEA mode settting. The ForeTrex works perfectly with the TH-D7, D700 and virtually all moving map programs running on PCs . I have tested it with Delorme Street Atlas, Topo USA!, UI-View, APRSplus, Visual GPS and others. The main connection issue is that, like the Radio Shack Digitraveller GPS, the unit's serial port won't start talking until it sees a non-zero voltage on the data input pin. Any voltage, positive or negative, of more than about 1 volt on the input pin will turn the serial port on. In other words, you can't use a simple two-wire (TXD and GND/COMMON) hookup. This presents no problem with either a PC or a TH-D7, both of which present a non-zero voltage (most PC ports are quiescent at -8 volts or so while the TH-D7 presents +5 volts out). This is a problem with the TinyTrak since it's data output line is set to zero volts during normal operation (i.e. when not being programmed). Probably the simplest way to handle the TinyTrak is to apply +5 volts from it's internal regulator through a 1K resistor to the data input line of the ForeTrex. The ForeTrex comes with an astonishingly heavy 5 VDC 500mA wall charger (apparently an old-fashioned analog 60Hz transformer design rather than the light-weight switch-mode wall warts provided with cell phones, digicams, home routers, etc). I measured the actual current draw and found it actually only consumes about 120mA inrush when the batteries start charging. Once charged, the unit draws only about 40mA to operate. I made up a cable from an old PS/2 mouse cable to steal 5VDC from my laptop external keyboard port; it works perfectly. It allows me to recharge or run the unit from the laptop's batteries or supply. I made up the home-made custom cable in the photo below. It combines power and data connections at the ForeTrex end, and branches out to DB9 data and PS/2 power at the PC end. This piece of shrink-sleeve artistry took me about an hour and a half to make! The biggest headache was finding a molded cable assembly with the micro-miniature coax DC power plug that mates with the ForeTrex. Both the DC power cable and the 2.5mm-to-2.5mm stereo patch cord are catalog items in the Philmore Electronics line of minor electronic parts. I made up a similar cable to steal 5 VDC from a USB port. [ Stardard USB ports can supply up to 500mA at 5 VDC to power devices plugged into them. ] -------------- next part -------------- An HTML attachment was scrubbed... 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