Drive a 1.8 degree stepper at 1 RPM

[ceefna]

Hi, the celestron brain has the coordinates of over 4000 astronomy objects in its memory. You align the telescope to 2 stars and input their positions. From this the software knows where the telescope is pointing.

You choose from the list of objects in the controller e.g The star Vega and the scope will move to where Vega is in the sky. Now without the brain and feedback from the encoders that would not work.

When you are wanting to take pictures of deep sky objects that you cannot see through the telescope only with long exposure then you have to be sure you are pointing in the right place.
I have found out that some of the larger Celestron scopes also have the L293DD, they use Pittman 8000 series motors so maybe this could be an option.

James, see what u did with the YouTube link. Duh, I feel stupid now.

Ceefna

[ceefna]

Hi Roman,
I appreciate all the help you gave me with the camera tracking mount. It works like a dream. I have a problem that I could do with some help on. I know you said it wouldn't be right to help me modify the motor drive board but would it be ok for you to help me fix it?
I am such an idiot, I was testing the logic supply voltage on the L293 between pin 20 and ground pin 16 on the schematic)and I had my multimeter plugged into amps and shorted something, duh.

The board still works, but the is a 10 second ish delay before it starts to track. Once tracking if I slew the motor to the right at full speed it takes about 10 seconds to start tracking again but if I choose a slower speed(you get 1 to 9) say 8 or below then it will track immediately. Its like it is having to re-charge/re-buffer before it starts to track again.
Now if I slew the motor to the left then it will start tracking again almost immediately. so its a problem moving right.
I have found a schematic for the board but I am not 100% sure that it is correct as it is not a professional one, here is a link.The PIC's on the board are 16F876A and the L293 is 20 pin so the schematic is wrong
http://www.dd1us.de/Downloads/Schema...oard%200v2.pdf

I have checked the input to the L293 on pin 7 (which is the motor turn right pin) with a led and it flashes away ok when slewing the motor as soon as the button is released the motor stops and should start to track straight away but nothing happens. You can see the led is dimly lit for about 10 seconds then it jumps into life and starts to flash as it tracks.
I hope you can understand this and have 5 mins to have a quick look at the schematic.
I think the L293 is ok as from my test it is not getting the signal to drive the motor from the 74HC240D for 10 seconds but what feeds the 240D. Could this be at fault? is it a lost cause trying to fix it? I am not sure I will be able to find a replacement.
Thank you for all your help

Ceefna

[hspalm]

I did a circuit on this subject for a customer
microHobby.net - Clock driver for Sparkfun EasyDriver breakout

[James Newton]

I did a circuit on this subject for a customer
microHobby.net - Clock driver for Sparkfun EasyDriver breakout

Nice, but the source code on that page seems a bit garbled... I don't see how the microstepping can possibly work as written and there are #includes that don't have files associated, and #defines that are run together on one line.

[RomanLini]

Yeah I checked the project out too. The microstepping is done by the onboard stepper driver chip James. However it only supports 8th stepping.

Also the coarse timer resolution means there is a limit to how many speeds it can run at, where the Linistepper code I posted for Ceefnas project will do 12th stepping, and uses a very high resolution Bresenham system for timing so it can do practically any speed with great precision.

And I probably should mention the linear driving of the motor current by the Linistepper means the stepper can move very smoothly (ie "stepless") at a tuned speed. An 8th step chip based driver is going to be a bit gritty for telescope use.

[hspalm]

Nice, but the source code on that page seems a bit garbled... I don't see how the microstepping can possibly work as written and there are #includes that don't have files associated, and #defines that are run together on one line.

Indeed, it's garbled! Haven't noticed, thanks for pointing out! I'm not sitting at the right computer right now, but it will be fixed soon. I'll update. (how strange is that post just above mine here, by nikki66?)