Autoguider adapter: USB to ST4 guide output DIY or fully assembled and tested

Updated June 1, 2010: Stock counts updated

Updated March 13, 2010: Price rollback: New vendors for some parts allow price rollback to original pricing!

Updated Feb 4, 2010: New EXE ASCOM driver setup

Updated Jan 2, 2010: Intoductory pricing has ended. I was able to keep increase to ~6%. Sorry but my costs just keep going up :-(

Updated Dec 20, 2009: New EXE ASCOM driver setup and for current availability

Updated Dec 20, 2009: Verified functional for Windows 7 device driver and ASCOM driver up to ASCOM 5.5.1

Updated Dec 20, 2009: One windows and ASCOM driver for all versions of Windows

Updated Sept 30, 2009

Updated link for mainstream PHD on MAC download

Introduced May 15, 2009

All information required to build this is included on this page

Add an ST-4 output port to your computer for autoguiding your ST-4 capable telescope

Supported by ASCOM 'telescope' driver using 'PulseGuide'

PIC based (18F2550) for USB as CDC interface (USB-serial port)

Bootloader capable for upgrades in the field (SW2 controlled)

Mac OSX Leopard support in PHD Guiding (added 6/9/2009), supported in standard release code

Click here for PHD 1.11 OSX

Craig's comments on Cloudy Nights

See Meade 909APM clone page:

See ASCOM guider software in action:

YouTube Video of Guide software

The video: “Enhanced 909 autoguider interface”

Another of my offerings, bluetooth wireless telescope control

Prototype USB-ST4 project page, unit on a perf board


Click here for installation instructions on a PC: XP/Vista/W7
Click here for INF file for XP/Vista/W7
Updated Feb 4, 2012: Click here for EXE version of ASCOM driver install, full source included, verified with XP/Vista and W7
Click here for ASCOM driver manual install version, full source included

Completed unit:

Circuit board dimensions: ( 1” x 3.7” , 25.4mm x 94mm)

Opto-isolated from scope. Two methods of isolation available:

Open collector pull to ground (Meade, Celestron, EQ6, etc), good for 10ma @ 5V pull to 0.1V, Volts up to 15V

Open collector optoisolator specs

Optical Photo MOS FET Relays (almost any scope, any polarity using 6P6C connector), good for 100ma @ 5V pull in, Volts up to 30V

Optical relay specs

Shown with open collector chip PS2501-4 above center, optical relay right
Same socket accepts 2 TLP227A-2 photo mosfets for solid state relay at higher costs


USB B connector, units draws ~50ma via USB power


ST4 – ‘straight’ through 6P6C cable
Simple Windows INF file required for CDC class, uses windows USBSER driver, no other hardware drivers required

MAC supports CDC, no driver required to use with PHD Guiding

Click here for screen shot on MAC OSX showing device
Terminal screen is unit responding to ^F (0x6h) 'are you there' command with an 'A'


USB VID: 04D8 PID: FFE5 (VID = Microchip, PID under sub license from Microchip to me)


Bootloader VID: 04D8 PID: 003C (VID = Microchip, PID = Microchip HID bootloader)


ROHS compliant (check parts lists with vendors specified)

Components rated to –40C


HEX files for bootloader, application(v2) and Windows INF file

Click hereto download –only- if you agree to:

1)      not re-distribute or host these files at any other location

2)      For private, non-commercial use only


See below for bootloader

Availability if you do not want to build one yourself

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.
There is an up to 5 business day ship time for non-assembled units
These are custom built and tested for 4-8 hours each
If this is not acceptable to you, please do not buy

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 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

As of Mar 1, 2013 All ports in stock for assembly and shipping.

All units RoHS

30 day return (except for buyers remorse)
buyer pays return shipping
One year warranty

Assembled and tested - $59.99 USD + shipping

Includes 6 ft USB A-B 28/24 cable and 7ft ST4 straight through cable

For Meade/Celestron, EQ6/etc

Assembled and tested - $64.99 USD + shipping

Includes 6 ft USB A-B 28/24 cable and 7ft ST4 straight through cable

For any scope mount (optical FET relays)

Mostly assembled -

Includes pre-programmed PIC, you need to solder ST4 jack, insert coupler chip and cutout the case, no USB or ST4 cable

For Meade, Celestron, EQ6, etc

Currently not available

Mostly assembled -

Includes pre-programmed PIC, you need to solder ST4 jack, insert relay chips and cutout the case, no USB or ST4 cable

For any scope mount (optical FET relays)

Currently not available


Email me if interested: astrogene1000_stuff AT



Parts list:

RS = Radioshack, M = Mouser, J = Jameco, D = Digikey










16 pin socket






6P6C PCB style






28pin socket



crystal 20mhz (-20C)



crystal Digikey 20mhz (-40C)






2 x 22pf



USB B Female R/A



Leds (2X)

697565 - LTL-4211N


8 pin sip 1k
resistor, isolated



4 pin isolated 1k



4 pin isolated 10k



tlp227a-2 x 2



28/24awg power USB A-B




PIC Development

The Microchip MCC18 compiler

Microchip MCC18 compiler


The full suite for USB dev is here:

Microchip USB page


USB framework and examples: MCHPFSUSB Framework v2.4

Base of project code: USB Device - CDC - Serial Emulator


I modeled after the "PICDEM™ FS-USB" eval board in the software, making changes to the I/O ports as dictated by my design.


Be advised: To recompile the bootloader firmware you -must- install the MCC18 compiler as 60 day eval to get optimizations or else the code does -not- fit in the boot section! (hence the need because IO port changes versus the PICDEM board).


HID Bootloader for Microchip

I used the “HID Bootloader - Firmware for PIC18 Non-J Devices” source model modified to match pins chosen for SW2

And the hidbootloader.exe from here:


The unit does actually scream along, with the various PLL's inside you can run a 4Mhz crystal and get 48mhz internal clock speed. I use a 20mhz because I find they start more reliably than the slower crystals.

Base schematic (matches PCB)

Cick here for PDF of schematic (Courtesy gdk, thanks gdk!)


Copyright GC @2009