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PC Interface --> Focus Motor

Pour la version Francaise, Cliquez ici :o)
Here is my "cheap but good" focus interface to make "autofocus" with Astrosnap !!! :o)

This interface can drive any DC motor, home made or not, replacing the old pad of your electric focuser ;o)
The power of the focus motor is only translating by the relays, so there are no risk for the PC if you do this interface correctly

The only thing to do, is to REPLACE the old pad, because using the old pad AND this interface simultaneously can do a short circuit on the powering of the focus motor.....
There is also two optional switchs to make electric focusing with this interface if you want, without using the PC :o)
If you have a home made speed controling systeme of the focus motor, you can still use it with this interface :o)

This interface is actually handled by the soft :
"Astrosnap, from Axel Canicio"
You can use it under the "Telescope" menu of the Astrosnap1.3 version :o)

It is obviously compatible, on the same parallel port, with the VP-SC or Tuc-SC webcam :
"Long Exposure Mod of Steve Chambers"

And with my parallel port guiding interface :
"Bond guiding interface" :o)

WARNING !!! i'm not responsible for any damage to your Computer if you are not sure of doing this interface correctly !!!

"THE" Prototype....
Better "look" than my guiding interface prototype !!! ;o>

Let's first see the electronic concept of this interface :

Now the upper side and components part list :

Components part list to use :

2 Bipolar Little 12 volts Relays
2 BC337 Transistors or equ (NPN)
2 3mm Red LED's
2 Diodes 1N4148
2 1Ko resistors (R1,R2)
2 10Ko resistors (R3,R4)
2 3.3Ko resistors (R5,R6)

Optionally: 2 mini push switches (S1 et S2)

Cable (2 wires + ground) to go to the Parallel port
1 parallel connector
(but you can solder the cable in an existing interface or modded webcam connector of course ;o) )
Other two wire cable for the power of the interface, the power of the focus motor, and to the motor :o)
WARNING !!! pay attention to correctly install the Transistor, LED's and Diodes witch are polarized....
Flate side of the transistor as indicated on the drawing, black line on the good side of the diodes, and short leg of the LED's on the flat side of the drawing LEDs :o)
For connecting this interface on the parallel port, you must use pin 21 for the ground, and pin 1 and 14 for the focus in and out commands by Astrosnap1.3 :o)

Printed board lower side :

Fot those who would'like to make a world market with this interface.... ;o)
Or more simply for thoses who would'like to see how to join the different components under the prototype board :o))))

Testing the interface :

You can test this interface by using a 9 volt battery, connected to the power input of the interface AND to the power input of the focus motor, while placing a voltmeter on the output focus motor points to see what happened...

When powering the computer, the two relays can close and the two LED's can light, but due to the "Bond cabling" of the relays, the motor output is to 0 volt, no risk for shorting the motor powering:o)
(Starting Astrosnap just switches off the relays and the LED's)

When in the "Telescope" menu of Astrosnap1.3, you can do the same test you can see on the image above:
On the Left : clic on "in",
On the Right : clic on "out",
You can see we have well an inverted output voltage on the motor, from the input motor of the interface


Good soldering, and HURRAY FOR AUTOFOCUSING !!!

Etienne Bonduelle :o)

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