This version of
ABOVE uses the serial port on the HP-50G to communicate with a GPS
receiver in NMEA, 4800 baud format, and with a Kenwood TH-D7A(G) Data
Radio. The calculator can be connected to these devices via
a cable provided by Samson Cables, or by a custom-made cable which uses
a level-shifter and an inverter. If the Samson Cables product is
used, you have to also use a null modem and a gender changer. Both of these items can be purchased at Radio Shack.
Some features use the Amateur Radio APRS (Automatic
Position Reporting System) protocol. It is documented elsewhere.
The added functionality is as follows:
- With the GPS receiver connected directly to the calculator, you can
- capture a position and save it. This is a substitute for manually entering position data.
- set the calculator's clock to GPS time.
The new menu entries are:
- You can compute future satellite passes and record alarms in the
calculator. Once the alarms are stored, they can trigger APRS
transmissions from the data radio. There are two types of alarms:
- Fixed alarms. They beacon the fixed station location stored in the calculator, or
- Moving alarms. They beacon the position received by the
GPS receiver. When the alarm fires, the GPS receiver must be
conncected to the Data Radio, and must be producing NMEA 4800 baud
- For either alarm type, the calculator may be turned off, but
the Data Radio must be powered on, and (for moving alarms), the GPS
receiver must be powered on. When the alarm fires, the calculator will
power up, and trigger the Data Radio. When the satellite is below
the horizon, another alarm will terminate the beacon transmissions.
Also, the functionality for two menu entries is different:
- INITIALIZE APRS:
- This sets the Power, Height, Gain (PHG) parameter that will be transmitted as part of a fixed position report.
- It also prompts for PATH and MESSAGE parameters. They are
required for fixed or moving position reports. See documentation
on APRS for the proper settings. In both cases, a the 4 last
choices are retained, and you can manually enter a new path or message.
- GET TIME FROM GPS
- It automatically grabs the time from a GPGGA sentence coming
from the GPS receiver. The GPS receiver must be connected
directly to the calculator.
- GET POSITION FROM GPS
- It prompts for a station name, from the existing list of stations, and stores the location for that station.
MISTAKE: While working on the upgrade to
2.0, I noticed an error when the positions of celestial bodies are
predicted. Basically, I used the calculator's time at the time
the predictions were made. Earth rotation was at the intended
time, but the celestial bodies were frozen at the time the predictions
were made, not the future time. Not-so-bad for stars, bad for the
planets, and really awful for the Sun and Moon. It's fixed in
- The output formats offered include "Moving Alarm" and "Fixed
Alarm". In both cases, a soft copy of the alarms is stored in a
file on the calculator.
- CLEAR COMPUTED PASSES
- It also clears all alarms, even those not generated by this program.
I have no affiliation with Radio Shack, Kenwood, HP,
or Samson Cables. I happen to use a Garmin GPS receiver.
They make good stuff. No one paid me to say that.
Also, use this program at your own risk. It's for
(Here we go with the dogs again...)
Bentley is our second
dog from German Shorthaired Pointer Rescue of New England. Please
consider adopting a homeless pet!