An enhanced clone 909 for the Meade AS 497


This page devoted to providing DIY build info and tech details of the Meade 909 functionality.


In addition, the base circuit board applies itself to standalone focusers and output to ST4 compatible scopes for guiding.


All the info required to build this is on this web page and the source is available at a link for all hobbyists and non-commercial entities. There is no permission granted to use this info or source downloaded by a commercial venture without express permission by myself.

All information on these pages Copyright © GC 2008


Please hit refresh on your browser to see the latest on this page


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Solution Graphics

See the companion project, USB to ST4 output dongle, for scopes with ST4 input already, or use with the 909

Another of my projects, control your scope wirelessly with a bluetooth connection

Update Update Nov 14, 2010 These units are in continuous stock, available to ship in 2 days or 5 days

depending on whether I have units assembled, I usually always have units assembled and tested.

If more than available stock is ordered I will refund money

immediately when oversold condition is recognized

( 24 hours max) and provide an expected availability date.

I am not currently stocking the USB interface cable. If interested in a full unit where you

purchase the cable and install (just plug in),please contact me.

The USB interface does not require a third party ST4 dongle for cameras that do not have native ST4 output.

The USB works only on PC via an ASCOM 4.1 driver available below

Please see YouTube videos for this unit HERE

Cost of this interface is approx $20USD plus shipping

Search for TTL-232R-5V (examples vendors, not associated)

Mouser (895-TTL-232R-5V)
and (TTL232R)

If interested, email me at: astrogene1000_stuff AT yahoo DOT com

I will only ship to North and South America, Europe, Japan,

Australia and New Zealand.

If you are from Italy -contact me- first for shipping quote

Orders from a country I will not ship to will be promptly refunded and not fulfilled

Note: If you have one of the 497 classics with any firmware version 3XXX/4XXX or a new Autostar 497EP with version 5XXX firmware or an Audiostar with version AXXX and an lx90 built 2008 onwards
This unit WILL PROBABLY NOT WORK out of the box but may require you to patch your
firmware for the 909 to be talked to!!! Contact me if interested for full details

Full featured: Guide/Focus/Reticule $69.00 USD

Plus shipping

Requires ST4 camera or ST4 interface from PC/MAC

See above for USB based version discussion that does not require external dongle

Full featured w/USB interface for guide $87.00 USD

(no extra PC to ST4 output interface required, PC ONLY) Plus Shipping

NO stock

Cost reduced Guide Only V4, NO focus/reticule/USB $39.99 USD

Based on version 4 design. Plus Shipping

Must be driven by ST4 camera or ST4 interface from PC/MAC

Can not be fitted with native USB interface

On the Paypal page, click on

"calculate total order amount" at the top of the page to see shipping charges

Assembled units: 30 day return (except for buyers remorse), buyer pays return shipping

One year warranty

No return on opened 'bag of parts' where assembly started

Picture of the new Guide Only unit May 20, 2009

-Based on original design now on a PCB, same code base
-Board dimensions 1"x2.7" (25.4mm X 69mm), case is 2"x3" (51mm X 76mm)

Full featured unit
If you are interested in different variations of full featured unit (see project page below),

email me. If there are any questions, email me.

astrogene1000_stuff AT yahoo DOT com

Picture of the full featured PCB Jan 18

-New connector style for reticule and temperature (could not find ready made cables for old style)
-Reticule drive circuit brought into PCB instead of in cable
-SIP resistor added for 1k Auxbus and pullups
-Ability to strap for USB powered when used as ST4 output device(-not- a 909!)
-Option for heavier passive pullups on ST4 lines (not used but available)
-Support for rs232 db9 removed
-Support for 8 pin 12F629 PIC removed (cost as much as the 16F628A!)





Older Availability

Full featured: Guide/Focus/Reticule Click here (more coming soon!)

Full featured w/USB interface for guide  Click here (more coming soon!)

Guider Only Click here (more coming soon!)

Any questions, email me:

astrogene1000_stuff AT yahoo DOT com

Video Tutorials

Enhanced 909 on the bench

Focuser temperature compensation in action

YouTube tutorial on using PHD and the USB guider

Coming Soon!

Build your own temp compensated focuser. Provides

stepper control and temperature sensor, either

with Aux Bus support or standalone, driven by

ASCOM driver via USB to clone

Guide output to ST4 compatible mount,

controlled via USB link from PC and ASCOM

driver. Sample pictures done with unit

Advanced 909 tech info

PHD Guiding andASCOM/ USB to  interactions

Interfaces supported

Schematic for PCB (basic)

Parts list for full featured 909

Powering capabilities

Serial commands supported

Full featured and expanded 909 on custom pcb

ASCOM drivers

ASCOM Driver for guiding only (updated 9/17/2008)

For full featured Guide w/Temp and stepper focus

Aux Bus Tech info

For the guider portion of the 909

For the focuser portion of the 909

Reticule Info

Source code

Code download for advanced – coming soon!

Code download for 'guider only'

History of this project

Started with a 506 clone





Full featured clone AND USB interface for guiding that goes with ASCOM driver below, assembled: Click here

Full featured clone: Guide, Focus, Reticule, assembled: Click here (back in stock!)

Guider only assembled:  Click here

Kit version:  Click here (kit version not currently in auction, link is old auction)


ASCOM 4.1 driver for guiding only via clone USB port, click me to download executable and source (Added 8/31/2008)

PIC of PHD Guiding to ASCOM driver and snoops of AuxBus and USB interface to clone and Aux bus comms(Added 8/30/2008)

ASCOM Driver for guiding only (Added 8/30/2008)

ASCOM 4.1 Driver added for enhanced 909 (Added 08/23/2008)

Serial commands supported  (Added 8/23/2008)

Powering capabilities (Added 8/23/2008)

Schematic for PCB (basic) (Added 8/22/2008)

Parts list for full featured 909 (Added 8/22/2008)


Full featured and expanded 909 on custom pcb (added 8/8/2008)

Ascom 4.1.1 driver to support the enhanced clone OOB serial guiding (added 8/8/2008)


Updated assembly guide for the kit (added 6/25/2008)

Theory of operation, assembly and testing the guider only unit (Added 6/18/2008)

View of kit components and assembled 909 functional guider only unit (Added 6/14/2008)

Better picture of the 909 guider only clone added (Updated 6/8/2008)

Updated source code to match new HW, included hex files for 12F629 guider only and 16F628 guider+focuser  (Old schematic version)(Updated 6/7/2008)

Updated schematic that has common base with 909 and 506 clone (Added 6/5/2008)

Added parts list for the full featured 909 clone (added 6/5/2008)

Added focuser support in code and schematic (added 5/31/200)

909 Guider only circuit layout using PIC 12F629 (added 5/27/2008)

Lowest parts count for the guider –only- capabilities of the 909 clone (updated 5/27/2008)

Part source: (updated 5/31/2008)

Tech info on the 909 and Aux Bus comms

For the guider portion of the 909

For the focuser portion of the 909

Reticule Info

Code download for guider only  (Updated 5/31/2008)


Updated 9/4/2008 – Sample pictures using the clone PCB as a guider –output-

I turned the ST4 port around on the 909 clone and drove the pins as
output to my lx200 CCD port.

300sec exposure
Imager: modified webcam on etx90 run at F8.8 (piggyback on lx200)
Guider: DSI on lx200 10inch @f3.1
PHD guiding used to ASCOM driver here.

The bright star is Altair
I could never do a 300 sec shot with the 10inch, my light pollution
swamps over 90 seconds

Original image:

(Note, I have a little flex between the etx90 and the carrying lx200, slight shift caused by this flex as Altair was near meridian)

4X blowup (250k JPG):

Small cropped section from 4X:



Updated 8/30/2008 – PHD and ASCOM driver for enhanced 909

Click the image for full size picture

Shows PHD in manual mode and snoops as PHD opens the ASCOM driver and of the driver to the enhanced 909 showing commands sent via USB and also the Aux bus communications from the 909 to the 497 in response to the PHD mouse clicks.



Updated 9/12/2008 – ASCOM driver for guiding only for enhanced 909  w/USB

I modified the ‘Telescope Simulator’ ASCOM 4.1 driver to provide a dummy telescope where the PulseGuide commands go out the USB to the enhanced 909 clone.


Driver available here (click me) (Version 4.0.2 update 9/17/2008)

Driver available here (click me) (Version 4.0.1 update 9/12/2008)

Driver available here (click me) (First release)


Only the Enable Pulse Guide, selection of Com Port and guide rate multiplier are exposed to the user on the setup screen (see below).


This all means that the 497’s serial port can be connected to any program and not just limited to your guider program.


The HBX view. Pressing a button when another program has the ‘Telescope’ connected sends 100ms guide commands to the enhanced 909 4 times a second as long as the button is pressed:



Setup screen:




Updated 08/23/2008 – ASCOM driver for enhanced 909 with serial interface

Setup screen:

A second serial port is added to the setup screen.

The driver will look for the enhanced 909 on the second serial port and use it for pulseguide commands. Status of the search is provided via a notify popup.


If the enhanced 909 is not found, it will use pulseguide to the 497 via the Scope serial port.



Download ASCOM 4.1 driver for Meade Autostar 497, click me


Updated 08/23/2008 – serial commands

Serial commands supported by the 909 clone

If the clone is attached to the USB to TTL serial cable or the rs232 section is populated, the following commands are available:


Guiding commands (supported by Meade Autostar ASCOM 4.1.1 driver)

:MgDxxxx#    Move(guide)

            Where D = direction as defined by ASCOM

            xxxx is milliseconds to move


:Rx#    Guide rate multipler

            Multiply xxxx of the MgD command by this value, default = 2, range 1-8, no checking done on input

            By default, ST4 input to the 909 returns a count of ~200 for every 100ms of pin assertion


Temperature (to be supported by Meade Autostar ASCOM 4.1.1 driver for temp compensated focuser):

:GT#   Read temerature, value returned is SCC.C

            where S = sign (+/-) and temp is in degrees Centigrade


Motor control (to be supported by Meade Autostar ASCOM 4.1.1 driver for temp compensated focuser):

:FSx#  Write x to the PIC port A, see next for bit assignments

            To drive a unipolar stepper in ('x' of command):

            Low torque full steps forward:

            0x1e, 0x1d, 0x1b, 0x0f

            Half steps forward:

            0x1e, 0x1c, 0x1d, 0x19,0x1b,0x0b,0x0f,0x0e


            See the FA command below for bit assignments


Input commands:

:FA#    Read value of PIC port A

            Bit        Use

            0          Motor control output bit F4

            1          Motor control output bit F3

            2          Motor control output bit F2

            3          Motor Enable output

            4          Motor control output bit F1

            5          Input, 0 = use Analog motor, 1 = use stepper motor

            6          Output to reticule, J4-4

            7          Input/Output for temperature sensor


:FB#    Read value of PIC port B

            If you are using the serial port for guiding, bits 4-7

            of Port B can be used for misc input, such as a home

            position sensor for the focuser to turn it into a true

            absolute position stepper focuser

            Bit        Use

            0          Input - Aux Clk

            1          Serial Rx

            2          Serial Tx

            3          Input/Output - Aux Data

            4          Input - Up/'North'

            5          Input - Down/'South'

            6          Input - Left/'East'

7                    Input - Right/'West'


Updated 8/23/2008 – Powering capabilities


Powering capabilities: Aux bus or external

Aux Bus powered: <180ma

16ma for basic circuits

15ma for H-Bridge

30ma for reticule (can be changed with 2 resistors)

~100ma for analog focus motor

(anyone know the draw of a 1206?)


Exceeding this limit does not damage anything but symptoms are:

200ma: Analog focus speed does not always go to max

220ma: focuser may continue to run but will stop on up/down next key


>240ma: Autostar may freeze while trying to focus.

What happens is the ground bounces while doing the PWM to the focus

motor and corrupts the Aux data line ( PWM pulses as 497 ramps speed

from 1 to 4 even though you have speed 4 set).


External power:

Somewhere over 650ma total draw, H-bridge gets warm after a few minutes, is rated for 1A/pin

This was tested with stepper motor and all winding energized.

Stepping with the little stepper I have was:

Half-step: 340ma

Low torque Full step: 170ma


Stepper is under full control of the 497 keypad, acts just like the

analog motor, 4 different focus rates included.


Port A of the PIC is fully accessible for writes from the out of band serial. 5 of the bits control the H-Bridge, one the Reticule out and one the temp sensor 1-wire. The last bit is used as a strap option for analog motor or stepper motor control.

Updated 08/22/2008

All the pieces hanging off the board:



Basic schematic for PCB, click image for PDF

Parts list for new PCB, click image for PDF

Update 8/8/2008

The following unit is expected to be available in the next week or two.

Source code to support the enhanced functionality will be available soon.


The first spin of the custom circuit board was successful and provides for:

·        909 guider only based on new PCB

·        909 full capabilities (guide/focus/reticule)

·        909 rs232 out of band (OOB) serial guiding (Ascom 4.1.1 modified Meade driver available now)

·        909 USB-TTL serial (FTDI chip) based for the OOB guiding (no need for extra PC to ST4 dongle)


·        506 rs232

·        506 USB-TTL serial connection to PC

·        506 w/response to the 1244 commands for controlling analog focuser or small motor

·        506 w/ST4 pseudo guiding via ST4 input (sends :RG and :M and :Q commands in response to ST4 input direct to the 494 via the Aux bus)


The firmware is still being developed for (the board does support it):

·        909 w/small direct stepper control for focuser and external power for stepper

·        909 w/temp sensor for stepper based temp compensated focuser, supported by modified Ascom Meade driver.

Just change the FW in the chip and populate different components on the PCB.


Board dimensions are 2.1 x 2.5 inches





Aux bus to the top, ST4 input bottom, Reticule to the left and Analog focus motor to the right



ASCOM 4.1.1 driver info to support the enhanced clone:

The source as distributed with ASCOM 4.1.1 was modified to add


I have been trying to work with the ascom-talk egroup and contact the current code author to be allowed to distribute a derivative work of the Ascom 5 Meade Classic and Autostar 1 driver but have been un-successful so far.

Please note: the Ascom 5 driver for Meade Classic and Autostar 1 as currently available on the ascom-standards website



Code snippet:


    If m_eModel = modelGPS And Duration <= 2000# Then

        ' use undocumented command deemed to be more robust, but its

        ' only valid to 2000 ms


        ms = Format$(Duration, "0000")

        Me.CommandBlind "Mg" & d & ms

        m_Util.WaitForMilliseconds Duration


'GC Added for enhanced 909 clone

          If m_eModel = modelAutostar And Duration <= 2000# Then

              ms = Format$(Duration, "0000")

              If g_GuideSerial.Connected = True Then  ‘ Send to out of band serial port if enhanced clone found

                  Me.CommandBlind1 "Mg" & d & ms

                Else    ‘ Send

                  Me.CommandBlind "Mg" & d & ms

              End If

              m_Util.WaitForMilliseconds Duration

'/GC End of added code


              Me.CommandBlind "RG"                ' Assure we're in Guide rate


              Me.CommandBlind "M" & d

              m_Util.WaitForMilliseconds Duration

              Me.CommandBlind "Q" & d


              ' classic only !!!, this is needed since once in a while one is not enough

              m_Util.WaitForMilliseconds 200

              Me.CommandBlind "Q" & d

          End If

    End If


It is expected the Ascom driver  for Meade will be augmented to support stepper based focuser and also adding temperature compensation in the near future once the enhanced clone firmware for same is developed.


Update 6/18/2008



For a full version of the document, please see:

Theory of operation, assembly and testing the guider only unit




The ST-4 interface supported by Meade telescopes is a 4 wire interface and provides a way to command the telescope to move in small increments based upon bringing a signal line low by an external piece of equipment. The guide rates are approx 10 arcsec/second of time for the AS 497.


Cameras that provide a 4 wire guide output interface are SBIG, Fishcamp and others.


Many telescope models from different manufacturers support this 4-wire guide interface input albeit with different pins or signal polarities.


The 909 offers this capability to owners of lx90's with Autostar 497 and to all almost all other Meade bases by utilizing patches available to the 497 firmware.


This interface can be directly coupled to cameras that support it or controlled via parallel port, button box, etc. Many programs provide support for this interface to guide your telescope.


The guiding provided by the 909 should be deterministic in that every ~100ms the Autostar asks the 909 if any inputs have been asserted and if they have been the 909 tells the Autostar for how long the inputs were set. The 909 keeps a running count so even if the Autostar is busy doing something else and an input is asserted the actual amount of time the input was set since the Autostar last asked is returned.


Update 6/14/2008

External view of assembled 909 functional guider only, looking at Guider port input (cord will be black in units supplied)

External dimensions are 3x2x1 inches (75x50x25 mm)



Internal view of assembled 909 functional guider only assembly (cord will be black in units supplied)



Pic of parts contained in the kit version of the 909 functionality for guider only.




Update 6/8/2008

Replacing the really bad picture of the 909 guider only clone.

See 909 Guider only circuit layout using PIC 12F629 (added 5/27/2008)

For what the board looks like from the bottom with the traces


Update 6/7/2008

Source now posted that matches pin definitions in the schematic. Hex files ready for burning included

Source for non-commercial use


Power was measured for the full featured clone including the H-bridge chip.

Guiding only: ~31ma

Focusing: 42ma

This was measured as drawn from the AS 12V line and includes an LM317T regulator.

All around chip tolerances may take this to twice that, which is why the 78M05 regulator is recommended if adding the focuser chip.


Plus the power drawn directly by the H-bridge L293D chip to feed the focus motor (my little motor as 41ma start and 33ma running full speed)


For those that do not want to go and download compilers and IDE the hex files for burning are now included.

Note: If using ICPROG to program the PIC’s:

For the 12F629 keep the OSCCAL value when it asks you, if you don’t the program will loop forever if you wipe out the instruction at the factory installed instruction at 0x3ff. Applies to ALL programmers actually. Read the blank chip and write down the value at 0x3ff!!!

For the 16F628, force LVP off in the check boxes. The code base sets it off and ICPROG forces it on, at least on my JDM programmer. If you do not force  LVP off then Pin RB4, Guider North/Up will be un-useable and the chip may actually go into programming mode in the circuit under rare circumstances.

For the changes to Hi-Tech C Lite (picl), navigate to the installed directory:

C:\Program Files\HI-TECH Software\PICC\LITE\9.60\dat

and add the following












Just after the same section for 16F627.

Big NOTE: The code produced by PICL may or may not work for the 16F628 if –ANY- changes are made to the code. Always compile with all optimizations off.

Reference in the Hi-Tech C Forums:


Enjoy, and if anyone builds one of these, I’d like to know (The astro community is a small one J

astrogene1000_stuff (AT)


Update 6/5/2008

Common hardware base for full featured 909 clone and the 506 clone.

Mix and match features in SW and HW.


Schematic, click image for larger view: (note the pins used for guiding and focuser have changed from the 5/31/2008 posting)

Now the source code lags behind the schematic, to be posted in the next day or two supporting the new HW.




OLD Parts list for full featured clone


Common pieces:
















18 pin socket
























14 pin socket








































CAP,CERM  .01uf
















78L05 5V 100ma TO-92





See below if Guider is added

















Serial interface -  - 506 clone + debug of 909 if desired:













16 pin socket
















CAP,CERM 0.1uf
















Guider pieces - 909 and 506:























Switches for enable and rate - micro type, no current handling required












Focuser pieces - 909 and 506















16 pin socket








CAP 100uf
























10k resistors





  Not required if Guider is added

78M05 5v 500ma TO-2

20  192233




  Regulator if Focuser is added

















Plus wire, connecto

r, etc.










Update 5/31/2008

Added focuser support in code and schematic

Adding the focuser requires going to a higher pin count PIC. The design below uses up 4 more pins (semi wasteful but then it would take another chip to invert the direction line to the H-bridge) This could be decreased to 2 pins and the power selection circuitry removed if the code did full PWM, coding exercise for another time J

The 2 pins would be the two direction selects, RB6 and RB7 if you always tied the L293D Enable line high (pin 1)


The focuser in the OEM 909 is based on PWM.

The basic cycle time is 5ms

For Speed :

Fine = 1.1ms power

Slow = 1.6ms power

Medium = 2.1ms power

Fast = 2.6ms power

After the ‘power’ is applied for the above time, the 909 reverses the polarity for 0.2ms then sets both outputs to the middle of the output voltage and ramps both down to about 3V. The next cycle it repeats the same.

I did not emulate the OEM using PWM but rather have two voltages, 5.1v/6.1v or 11v+ (not 12v+ because of voltage drop through H-bridge)


Fine and Slow get you the low voltage, Medium and fast get you the high voltage.

PWM could be added in the code by manipulating the PIC pin RB5 to Enable/Disable the H-bridge  for ‘Fine’ and ‘Medium’ speeds at their respective voltages but this would –not- get you the nice ramp of the OEM.


The code honors the focuser commands from the AS, see “For the focuser portion of the 909of this page.

Schematic (clink image for larger view)

The transistors I used are just small signal type with Abs Max of 0.6amp and 625mw. The L293D is good for twice that. The L293D uses the ground pins as part of its thermal management, all 4 MUST be connected!


The OEM also has an 8ohm/1% current limiting resistor in one of the lines to the motor, I did not include that but is probably a GOOD IDEA! This would cap you at 1.5amps/12V but if you do that the Aux bus power line really starts to droop J


How much power can the following drive to a focus motor? I am not sure. I have an old small gearhead 12v that I used on my lx200 for a focuser and it requires about 40ma. This circuit did not have any problem with that. When I loaded it to 250ma (basically by shorting the motor pins, it drew 250ma and the diode and PNP transistor got hot and the PIC crashed. An alternate design for the power would be as above, do full PWM or play with the adjust voltage on an lm317T by imposing a second resistor between adjust and PIC pin RA6 and switching the resistor to ground or letting it float thereby providing two different voltages.


Old old schematic:


Deleted, old


Also a note on the OEM, I have found if you are really beating on the up or down key the AS seems to loose it place and it does –NOT- send the stop command to the focuser. This is not a function of how long you hold it down but of repetitive presses. Pressing either Up or Down will get the AS back in sync and the motor will stop.

The was with version 43gg.


Update 5/27/2008

Layout for guider only and 8 pin PIC

Yes, pin 1 is Vcc and pin 8 is ground!

Use a socket for the chip!

Layout shows the copper side of board, components go on the non-copper side and feed through the holes.

!!!Use care in connecting to the Aux Bus pins. Reversing power and ground can be detrimental to all parts, including your SCOPE! Reversing Clk and Data will just cause it to not work.

If you want to use Radioshack perf board 276-170 , use the layout shown in the picture of the prototype below

and cut the board down to size. Same pins for Up/Down/Left and Right apply for the PIC chip.


Connect the right side of 680ohm to the right leg of the 5.1v zener –underneath- the board, careful not to short anything!  (no more holes!)


Deleted, old



Update 5/21/2008

Lowest parts count for the guider –only- capabilities of the 909 clone

4 resistors

2 capacitors

1 zener

1 PIC 12F629

plus connectors, cables, etc.


The code is working for guider only. I have not cut in the parts to ignore the reticule and focuser commands from the AS yet.


The following is a picture of the prototype supporting the guider functionality of the Meade 909.

Current draw = 10ma as measured from AS 12V line. I replaced the 680ohm with a 4.7k ohm and it ran but would periodically restart every 10-20 seconds (4.7k showed 1.6ma draw).


Pin 1 is lower right. Pins 2,3,4 and 7 are used as guider inputs. Pins 2,3 and 7 have internal nominal 20k pull-ups enabled. Pin 4 does not have this capability so the 10k is added.


Picture updated 5/27/2008 to show 10k pullup from pin 4 to the zener power.


Deleted, old


Part source: (updated 5/31/2008)

From Jameco (no affiliation with them)

MICROCHIP CORPORATION PIC12F629-I/P          223790      1    $1.49     $1.49

DIODE,ZENER,1N4733A,5.1V,1W                                 36097    10   $0.08     $0.80

RES,CF,680 OHM,1/4 WATT,5%                                         690822  100    $0.01    $1.00

RESISTOR,1/4W 5%,220 OHM,                                      30471       1    $0.99    $0.99

RESISTOR,1/4W 5%,1k OHM                                         31237       1    $0.99     $0.99

CAP,TANT,10uF,25V,10%                                               94080        1    $0.31     $0.31

CAP,CERM,DISC,.01uF,50V,20%                                  15231    10    $0.067   $0.67

SOCKET,IC,08PIN,MACHINE TOOLED                     662573     1    $0.22      $0.22

MODULAR JACK,6P6C,W6"LEADS                             124039     1    $1.25      $1.25

RESISTOR,1/4W 5%,10k OHM                                        30058       1    $0.99     $0.99


Total: $7.72  Shipping = $5.95

For those of you that do not like zener’s, use the:

78L05, 5V 100mA VOLTAGE REGULATOR, TO-92      51182  1  $0.29 $0.29


Focuser parts:

1341966 QUADRUPLE HALF-H DRIVER                 1341966    1      2.69      2.69

TRANSISTOR,2N4401,NPN,GP                                     38421    10       .08        .80

TRANSISTOR,2N4403,PNP,GP                                      38447    10       .047      .47

 10k resistors                                                                    691104    100    .01      1.00

5.1v Zener                                                                           36097     10     .08        .80


6.2v Zener                                                                        178802      10     .049      .49

Plus wire, connector, etc.

Total:  $6.25 and you get a lot of spares!

Radioshack pieces:


Dual General-Purpose IC PC Board                  276-159  1   $2.49

Project Enclosure (3x2x1")                  270-1801 1   $2.29



Project Box and PC Board Combo                   270-283  1   $0.97



Matching Printed Circuit Board with 550 Connect Points  276-170  1  $3.49


You end up with: 98 spare 1k, 680 and 10kohm resistors, 9 spare 0.01uf, 9 spare 5.1zener's, 1 spare 20 pin IC board


AuxBus cable DIY

CONNECTOR,RJ11,4P4C,STRANDED            103491    10  $0.132         $1.32

MOD NET CBL,RJ11-6P4C,7'L,                        115554                  1  $1.75           $1.75 or the one laying in the drawer, 4 wire stranded

(cut off ends, use to make AuxBus cable with the above connector, also need a crimper to do this)


Technical info on 909 and Aux Bus

For the guider portion of the 909

First byte = byte count -from- the 497
Second byte = Aux bus address 497 wants to talk to
Third byte = command to the external device
4'th and subseqeunt bytes supplied by the external device
4'th byte = # bytes device wants to send
5'th, 6'th, etc bytes: data from device

All snoops taken with PIC based Aux bus sniffer, a by product of the
506 clone I did.

AS 497 Aux bus startup sequence

02 56 00 First thing sent
02 06 00 FF Poll for device address 6, no response (the FF)
02 07 00 FF Poll for device address 7, no response
00 00 00 00 Aux bus reset (??, see the patent)
02 27 00 01 02 Poll for 909 (address = 27),
909 responds (the trailing 01 02)

Once the 909 responds, the 497 starts polling it every ~100ms asking
for guider info.
The guider info returned is the the amount of time in the 100ms the
given direction was asserted. For every ~0.51ms the direction was
asserted the 909 increments or decrements the count. If a signal is
asserted for the full 100ms then the count would be approx +/- 192

The count is returned as two signed 16 bit integers
1'st integer = up/down with more down than up being a negative number
2'nd integer = left/right with more left than right being a negative

If both up and down are asserted for the full 100ms interval, a 0 is

The 497 uses command 05 to ask the 909 for its guider info.
909 responds with byte count of 4 and if none of the inputs asserted,
both values =0

AS: 02 27 05 909: cnt = 04 up.down = 00 00 right/left = 00 00

Up asserted for 100ms
02 27 05 04 00 C3 00 00

Down asserted for 100ms
02 27 05 04 FF 40 00 00

Right asserted for 100ms
02 27 05 04 00 00 00 C3

Left asserted for 100ms
02 27 05 04 00 00 FF 46

For the focuser portion of the 909

If you ask me the focuser comms are a little hokey. When you press up
or down the 497 sends 1 to 4 commands, based upon the speed setting,
on 100ms to 200ms intervals (can be back to back or interspersed with
guider polls). Basically if you just tap the up/down key it starts out
at fine and the longer the key is pressed the faster it will go, up to
the max of the speed you have set. This means that it can take up to
0.7 seconds to reach full speed (from 0.3 to 0.7 seconds).

497 to 909 for focuser start with:

WIth DIR = 1 = UP, DIR = 2 = DOWN

The 'speed is controlled by the number of these commands you receive
and how high the count is

A single 0x7,0x27,0x4,DIR,0x0,0x1,0x0,0x6 received = FINE

Receive for SLOW:

Receive for MEDIUM:

Receive for FAST:

The STOP command is a single xfer of

Note: there does not seem to be any type of ack from the 909 for the
focuser commands. The 497 sends 8 bytes and does not seem to keep
gating out clock after the last byte so the 909 can ack it.

Reticule Info

The reticule info is placed on a separate page, it is deserves its own page J

Click here for reticule info