Advanced Astromaster Setting Circles

RS-232 Interface

The Advanced Astromaster has the ability to connect to a computer and several of the commercially available software packages will talk to the AAM. Celestron does not provide much information about connecting the AAM to a computer, but here is an article found in the Celestronuser listserv that describes the process very well.

From: gary@pacsemi.oz.au (gary kopff)

Subject: AAM RS232 and External Power

Date: Fri, 11 Oct 1996 15:23:41 +1000

To: celestronuser@lists.best.com

Hi Folks !

 

Recently I posted an article regarding connecting the Advanced Astro Master (AAM) to a computer via an RS-232 serial interface. I have now added some extra information which describes how to power the AAM using an external DC power supply. I hope someone finds this information useful.

Gary Kopff

Mount Kuring-Gai. NSW. AUSTRALIA.

gary@pacsemi.oz.au

 

------------------------

 

CELESTRON ADVANCED ASTRO MASTER

COMPUTER CONNECTION

DESCRIPTION

 

Thanks to those who replied to my request regarding the RS-232 interface pinouts for the Advanced Astro Master (AAM). In particular Scott Kroeger's <Scott.Kroeger@mei.com> suggested procedure enabled me to deduce the pinouts very quickly. Thanks Scott for a great description. I also received some information about the B+ pin from a gentleman in California. Apologies for not acknowledging you here as I have misplaced your email and with it your name but thanks all the same !

 

Here is a description of the pin assignments. With this description one can go to your local electronics store, buy a standard telephone cable and a DB connector and make your own cable and possibly save some dollars. You can also use this information to power your AAM from an external DC power source to save on batteries.

 

DESCRIPTION

-------------

There are two RJ-style receptacles on the back of the AAM. When looking at the AAM from the rear with its keypad facing up, the left hand receptacle is for the encoder cable and the right hand receptacle is for the RS-232 interface. Note that the RS-232 receptacle has 6 pins. In Figure 1 below I have labeled the 6 pins from left to right according to my own

convention.

_________________

| --- |

| | | |

| - - |

| | | |

| -- -- |

| | | |

| | | |

| | | |

| | 1 2 3 4 5 6 | |

| |_____________| |

|_________________|

 

Fig 1.

View of 6 pin receptacle

for RS-232 interface looking

at the AAM from the rear.

 

 

The receptacle pin assignments are shown below

in Table 1.

 

 

Pin 1 - NC (No Connect)

Pin 2 - B+ (9V to 15V - NOT VERIFIED - See below)

Pin 3 - Ground

Pin 4 - RXD

Pin 5 - TXD

Pin 6 - NC

 

Table 1.

6 pin receptacle pin

assignments.

 

You can buy a telephone extension cable with 6 pin plugs or you can buy a more common telephone extension cable with 4 pin RJ-45 plugs instead. Mechanically the 4 pin plug will still fit into the 6 pin receptacle, but pins 1 and 6 of the receptacle will be inaccessible. This isn't a problem, as you can see from Table 1, since receptacle pins 1 and 6 are No Connect anyway. Figure 2 shows a view of an RJ-45 plug with the arbitrary pin assignments that I have chosen for the purpose of this description.

 

------- <---- retaining clip

-- --

| |

| |

| |

| 4 3 2 1 |

|_____________|

 

Fig 2.

Pin assignments of 4 pin plug.

View of 4 pin plug is when looking

at plug from front with retaining

clip at the top.

 

 

Table 2 below shows the mapping for the pin assignments from receptacle to RJ-45 plug.

Receptacle

Signal

Plug

Pin 1

NC

No Pin

Pin 2

+B

Pin 1

Pin 3

Ground

Pin 2

Pin 4

RXD

Pin 3

Pin 5

TXD

Pin 4

Pin 6

NC

No Pin

Table 2.

Mapping of pins.

 

HOW I MADE MY CABLE

-------------------

I bought a 15m telephone cable with 4 pin RJ-45 plugs at both ends. I cut one of the RJ-45 plugs off, stripped the wires and soldered on a DB connector suitable for my computer. The conductors in the cable are color coded. Most PC's will have a 9 pin DB connector, other types of machines will possibly use 25 pin connectors. I will leave the details of the computer end of the cable up to you as this will change with different types of computers. You should note that the AAM's RXD line should connect to the computer's TXD line and the AAM's TXD line should connect to the computer's RXD line (i.e., the signals should cross-over). Signal GROUND should be connected to the AAM's Ground line. Your computer's serial port should be set to 8 data bits, 1 stop bit, 9600 baud, no parity. When you turn on the AAM, it reports its software version number immediately, e.g. V3.5 The AAM is then ready to receive the 'P' and 'Q' commands (upper case only) as noted in the manual.

 

POWERING THE AAM WITH AN EXTERNAL DC SUPPLY

-------------------------------------------

The AAM's B+ pin can be used in conjunction with it's Ground pin to provide external power to the unit. This can be useful if you want to save on batteries. Connect B+ to the + side of your DC power supply and Ground to the - side. It may be convenient to make these connections within the plastic backshell of your DB connector. I ran an extra pair of wires from within the backshell to a DC power supply. Make sure that the connections are well insulated with heatshrink or PVC tape to prevent a short occurring within the backshell. Information I received from one individual suggested the DC power supply can be between 9V and 15V. THIS INFORMATION IS NOT VERIFIED. I have powered my AAM with a 14.8V supply with no adverse affect. There is no need to remove the internal battery when powering the unit with an external supply. Be sure to check all connections before turning on your power supply and the AAM. If possible, check with a multimeter first.

Alternatively, if you are not interested in having an RS-232 computer cable for your AAM but are interested in being able to power it externally, then you can simply make a cable that does not include the RXD and TXD connections. In this case you can substitute a more convenient connector for the DB connector. I made a second cable with an RJ-45 on one end and a car cigar lighter plug on the other. I also have a Celestron cigar lighter cable for powering by Celestar. This cable has a phono plug on the other end. From an electronics store, I purchased a twin cigar lighter plug - like a power double adaptor for cars - for about US$5. I can now power the telescope and the AAM from the car or other portable power source while in the field.

 

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