My astronomy project:
Stepper motor focus driver

Content:

1. Collecting information
2. Hardware tools for development
3. Arduino Nano and DRV 8825
4. Prototype setup
5. Setup Arduino system
6. Schematic / setup
7. Start assembling circuit board
8. Setup INDI for MyFocuserPro2
9. Enclosure
10. 5 kg load test
11. High impedance stepper motor
12. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

3, Arduino Nano and DRV 8825:

Always a lot of other projects to do, travel and the car. But now I'm back to this exiting project. My smaller telescope, or lens, a 300 mm f/4 medium format works so good and now I must have my bigger APO refractor working again.

I was just to order the needed components when I remembered that I got a present from my friend, an Arduino Nano. The instructions says I should use the Arduino model NANO CH340G. Not exactly the same, I must check if I can use this one.

The original design use an ULN2003 driver for the stepper motor. That is a Darlington design and it can only sink the current. That design only works on unipolar stepper motors, they have divided the coils in two sections. I have the more common design with bipolar stepper motor and need a symmetric driver, in this case the DRV8825, data sheet pdf: DRV8825. The trim potentiometer set the current to the stepper motor's coils.

Circuit board layout:

There are not many component because there is no need for a display or DC/DC converter. I can use a simple prototype board, I hope at least. To left is the 12 Volt power cable and its connector. Right above is the cables for the LEDs, only two of them needed and cut in half.

I need to add two 4k7 ohm resistors and a 330uF capacitor. A fuse for the incoming 12 volt power. The 5 volt is taken from the USB. Two buttons are needed too, move focus IN/OUT.

The driver and processor sits in sockets and are easy to replace.

On the driver a heat sink must be installed. Later I design box for it that I 3D-print.

I try to built it as simple as possible. In the original drawing there is a 12 to 5 volt converter, I don't need that. I always have it connected to the USB Hub and then it get the 5 volt from the USB.