Steve's Things

For the last few days I’ve been working on the electrical portion of an astrophotography mount for my camera. The mechanical portions were built by my father and I’m handling the electronic portion of the device. Basically, for those who don’t know, this device is designed to allow one to take long exposures of the stars without them blurring due to them moving across the sky. This device moves the camera in such a way that allows for said movement.

Originally, my father and I spent a day working on both the frame and the electronic portions of the unit. I quickly whipped one up with a protoboard I had laying around and a PIC16F690. I used an SN754410NE H-Bridge driver for this design as well. Unfortunately we didn’t finish the project that day, and I wasn’t keen on programming the PIC having to pull it out of the IC socket every time I wanted to test it.

The original defunct board. This board was omitted due to the fact that it had no ICSP provisions.

Anyways, many months have passed since then so I decided to finish ‘er up. This time though I wanted the underlying design to be flexible enough to handle any configuration of “barn door” and to allow for nice methods for both calibrating and homing the device, whereas most DIY methods are rudimentary at best. The reason I want to make it more robust than needed is due to the fact that I believe that a nicely finished electronics board kit may sell quite well, or perhaps even the entire unit if done in a low-cost, high quality way.
Here are some of the planned features:
1. Multiple configurations built-in for both screw pitch, motor step angle and “barn door” configuration
2. Homing and End Range Switch provisions to allow for homing of the device and mechanical damage prevention.
3. Support for 12 and 16 button keypads.
4. Support for 8×1 or 16×1 HD44780 LCD displays. I choose these because they’re cheap and formatting for this style guarantees compatibility.
5. Multiple drive options, Full-step, Half-Step, Strong movement, weak movement.
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Anyways, Here are some images and descriptions of how I put it together, up till now. As of this writing, it’s not finished yet. It will take some time methinks.

First, I took some Stripboard and planned out the pinouts and connections. Stripboard (or veroboard) is my favorite since it’s so damned easy to plan. Despite there being a great many other protoboards out there, veroboard has been the most useful, for me anyways.

Planning it out

Starting the board

Halfway done

Board pretty much complete

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There were a few kinks to work out but not many, despite how messy this board is. 🙂
It took me a while but I got the keypad, LCD and Stepper running. It didn’t take very long for the LCD and keypad since I’d already developed my own libraries for those functions. I then played with the stepper motor and got it working.

Astrophotography electrics working with keypad, LCD and stepper motor

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Now, to mount it in the enclosure. I just happened to have an ideal enclosure and a sealed lead acid battery from princess auto. The battery charged fine and I think it will serve quite well to run the stepper (This motor draws about 200-400ma depending on drive configuration). Here’s what it looks like as of today. 🙂

Electrics in Enclosure

I’ll have to give the enclosure some rubber feet since the mounting screws jut from the bottom but that’s cosmetic at this point.

Anyways, I’ll report further progress, as usual, on my blog here.

Here are some interesting links
http://www.keteu.org/~haunma/proj/barndoor/
http://www.cs.uiowa.edu/~jones/step/types.html

Comment if you wish.