Add A Remote Two Speed Focus

[Dennis G]

The attached circuit diagram has been proven and is simple to build on a square of vero board. The copper lands do not show in this scanned attachment, they run vertical and the used portion is shown lined in. The small geared head 12v DC motor, 30 RPM No YG2734 from JCar.
TWO SPEED REMOTE FOCUS CONTROL CIRCUIT
Reading the Iceman’s article PLANETARY IMAGING WITH A MONO CAMERA and noting his comments, re the importance of a slow focal adjustment, I submit here the circuit and picture of the two speed focus drive fitted to my telescope, which has a 10:1 reduction focuser control. The motor drive and rotation speed could be modified to suit other types of focusers. The One Shot hand held controller consists of a small plastic box with a 3 mm thick aluminium lid, which acts as the heat sink for the BD681 PNP transistor. The on/off 12v dc power switch has a telltale led. The direction is changed with a slide switch, which is easily identified in the dark and the speed switch is a toggle switch toggled crossways.. Each pulse is switched by the push button switch. The circuit layout uses a small square of quality Vero Board with hole spacing to suit the 14 pin IC plastic base connector.
Note the layout shows the component side and the x marks are where the copper lands are cut. I use a 5 mm drill to cut through the copper lands where needed. Note. Just cutting the copper, not right through the board. I’m happy to answer any questions, on Forum please.

[Karls48]

Hi, I don’t want to be pain in the neck but BD681 is a Darlington NPN transistor, not PNP. I have used those transistors at work for about 10 years.

[AlexN]

I like it.. looks like a good plan to me... One question, have you tested it in the field yet? does the rubber O ring get any slippage in damp conditions?

[Dennis G]

karls 48. Sorry to give the transitor the wrong polarity but the number is correct BD681. Thanks for pointing this out to me.
Alex N. Yes, it has been working on my original 8 inch dob and on my new 10 inch Light Baucket for a few months and only an hour ago I used it to focus the scope with the new DMK imager test from my living room window. Have a look in the equipment section of IIS. The control shown doesn't have the two speed switch this was added later when I found it was required to get that little bit closer focus. By changing the C you can adjust the amount of rotation required. larger value will provide greater turn and smaller less turn . No, the O ring which is 2 mm thick doesn't slip. . Be sure to have two or three on hand because they will eventually break. Don't chose one too small with a lot of stretch, it isn't needed. One important point to remember if your focuser is as shown, the adjustment knobs must be correctly set or you can make the focus movement too tight. Thanks for your comments If you have never worked with Vero Board be sure to check every copper strip for solder bridge and use a base for the IC . I inspect my work under a strong magnifying glass befor powering up.