10
COMMUNICATING WITH YOUR MOUNT
The GTOCP4 and GTOCP5 (abbreviated CP4/5) introduce communication alternatives in addition to the venerable RS-
232 serial ports (both serial ports have full functionality for keypad downloads beginning with version VCP4-P01-14)).
These are USB, Ethernet and Wi-Fi. Each will be discussed individually below, but a bit of introductory text is in order.
First off, you must understand that ALL control, information and operational data passing to and from the mount is in
the form of simple ASCII characters in text commands and responses. Whether you are controlling the mount from the
keypad, from a computer, or from a smart phone or tablet, an order to slew the mount will consist of the exact same
commands, made up of these same ASCII characters, sent in the exact same order, and basically at the same speed.
Do not be duped into thinking that traditional serial communication is somehow inferior to USB, Ethernet or Wi-Fi. Your
goal is to select the alternative(s) that best meet your needs with respect to your control device, and the distance between
the control device and the mount. Crash-proof dependability of the communication medium is FAR MORE IMPORTANT
than high speed!
Regardless of the communication method, when you are controlling the position of the mount with a computer program
such as the Astro-Physics Command Center (APCC), DC3 Dreams’
ACP™
, or Simulation Curriculum Corp.’s
Starry
Night™
, there is constant communication between the computer and the microprocessor in the CP4/5. The computer
software requests constant updates to the position and status of the mount, and the CP5’s microprocessor chip responds
with continual RA and Dec coordinate data via the cable or wireless connections to your computer. When you use the
software to give instructions to slew to a new object, the commands (RA and Dec coordinates) are sent to the mount.
Equatorial Servo Logic" on page 36 for additional information.
As a final introductory note, remember that the CP4/5 is the “brains” of the system. The mount won’t quit if your control
device is disconnected for a while, or if you change connections mid-session. For example, at a large star party, there
may be a ton of competing WiFi networks flooding the air waves. If 10 minutes into a 20 minute exposure, you realize that
the WiFi is flakey, you can disconnect and then reconnect with USB, serial or an Ethernet cable. You can plug in and then
unplug the GTO Keypad at will without issue. The CP4/5 will simply continue on regardless
Choosing Your Communication Interfaces
Distance of Mount from Control Device
One of the primary factors in choosing your connection method(s) will be the distance separating the control device from
the mount.
●
Computer closer to mount: People who have their mounts close to the controlling computer, and do not have network
capabilities at hand, may find direct USB connection to be their most convenient choice. For mobile setups like
observing in your backyard or going to star parties, Wi-Fi is a flexible solution.
●
Computer further from mount. Somewhat longer distances may be better served with peer-to-peer Ethernet, a cabled
network connection to a router, an installed serial card or a USB-to-serial adapter and a longer serial cable. For
control of a mount that is within 100 yards or so of the controlling computer, we have found the Icron Technologies
Ranger 2304 USB extender to be an excellent solution.
Remote Observatories
Remote observatories will generally require a computer or an IP addressable server in the remote observatory itself, along
with a high-speed internet connection for communication with your home computer. The Ethernet and Wi-Fi discussed
below will prove helpful. However, such complete long-range solutions are beyond the scope of Astro-Physics to supply or
support.
If you are outfitting your observatory with a new computer, you might want to consider a small industrial computer or
media-player computer like the Global Shuttle DS series (i.e. the DS57U or newer), the Cincoze line, or the Moxa V
series among others. These computers are used to run the huge video billboards that are now everywhere, and they are
environmentally robust, even at low temperatures. They also come with multiple true serial ports, and many operate on 12
volts - perfect for the solar-powered observatory! As with any computer electronics, change is the only real constant.
USB Port 2.0
The USB port uses an on-board FTDI RS-232 serial UART to seamlessly connect as if it were a true
serial port. This device is powered both from the USB itself and also from the power of the CP4/5,
providing an extra layer of redundancy over external USB-Serial devices. Because the internal FTDI
