Christmas (arrrrrh!) Project - part II (the focuser comes!)

[Stargazer33]

Here is my first attempt at a schematic for my electronic focuser - well as you may have noticed from the file name, it is actually my third, but the first one posted! Most of it has been stolen...er...borrowed from KCOTARs build.

As giving me an electronics project is like giving a three year old a shotgun and a pot of paint and asking them to paint a Fabergé egg, I expect there is a lot that is wrong with my schematic!

And as for the code to run it ... well, imagine the same 3 year old with the keys to a nuclear missile facility!   It isn't going to end well!

I'm not too sure how much voltage I will need to run to the switches; hopefully I can make use of the 5v feed from the UNO. They have 12v LEDs in them which I was hoping to light (at reduced brightness) so that I could easily see the buttons in the dark.

My intention is to use the buttons on the handset when I am doing visual observing and then plug the laptop into the USB socket and control the focus from either Sharpcap if I am using the web cam or APT if I am using the DSLR.

Any help, guidance or suggestions would be most gratefully received from myself and probably my wife as she is the one that will have to suffer all the swearing and flying bits of electronics and tools come Christmas. 

[Gina]

The 5v output from the Arduino will not be capable of driving the stepper motor - you will need a separate supply.  Apart from that the diagram seems fine   You want to run the switches from 5v as that's the maximum input voltage on the Arduino inputs.  I take it these are momentary contact switches (like push buttons).

[Stargazer33]

Thanks Gina! The stepper motors I have got coming are the 5 Volt ones with their own driver board. Will the 5 Volt output from the UNO not be enough? Is it because it won't deliver enough amps?

The switches are indeed momentary ones, I thought that would be best. I was going to have one pair as slow forward and reverse and then the other pair as fast forward and fast reverse. Can I take the 5v output from the UNO to run these or will I need a separate supply for these too?

[Gina]

Thanks Gina! The stepper motors I have got coming are the 5 Volt ones with their own driver board. Will the 5 Volt output from the UNO not be enough? Is it because it won't deliver enough amps?

The switches are indeed momentary ones, I thought that would be best. I was going to have one pair as slow forward and reverse and then the other pair as fast forward and fast reverse. Can I take the 5v output from the UNO to run these or will I need a separate supply for these too?

I can't remember off-hand how much current these stepper motors take but I know it's more than the Arduino can supply without overheating.  The switches only draw a mA or so depending on the resistor in series with the LED so could run from the Arduino 5v.  Also, remember that any current you draw from the USB must add up to less than 500mA - again not enough to power stepper motors.

[themos]

You can't feed 12V to the Arduino! Also, as Gina says, you need to feed the stepper coils from a separate power source. The low-voltage steppers will draw a lot of amps, and even the 12V ones will draw close to half an amp. So, you red wire must not be connected to the Arduino but to the +ve of the power source (and the -ve of the power source connects to Arduino's GND).

For the manual control, I would make a separate box with a 12-way rotary switch that just connects the motor voltage to each of the windings. I connect positions 1-4  of the switch to the four coils  and also connect 5-8 to 1-4 ( so that 1 and 5 are connected, 2 and 6 are connected and so on) and also  connect 9-12 to 1-4. Then, instead of stepping the motor by pressing buttons in sequence, you just turn the rotary switch (and it works clockwise for forward, anticlockwise for reverse).

[Stargazer33]

Thanks for the replies! The push buttons arrived today and they look a bit big! Possibly too big to fit into my enclosure even with the contact pins bent out at 90 degs.

I like the rotary switch idea - sounds simple (but then so did my original idea!), but I would like a fast forward/reverse option too if possible.

On the Arduino site it says that the UNO DC socket has an recommended input voltage of 7v-12v with a limit of 6v-20v. Is this not the case?

[themos]

It looks like the UNO will take 12V but a power tank can put out 13.5 or more and I am not sure the voltage regulator on the UNO will cope. I know that I experiment with a "big" Arduino when I am developing (I have the Duemilanove) but switch to a "small" production Arduino for deploying the project ( I use the Mini Pro). The small ones don't have voltage regulators so I am in the mindset that says "only feed 5V to the Arduino". Luckily, it gets that from the USB connection. I would not be tempted to share motor power and arduino power, it's a recipe for hard to diagnose problems. 

It should be possible to use a rotary switch as an input to the arduino for single steps while also providing fast-forward and fast-rewind buttons. I haven't seen a "sketch" that does that but there could well be one out there.

[Gina]

Yes, agreed   Let the Arduino run off the USB and provide a separate supply for the stepper motor and driver.

[Stargazer33]

Thanks again!

Looks like I will have to add a USB hub to my last years Christmas project! I don't really want to have to use the laptop when I am just doing visual. I was intending to use the push buttons for adjustment when doing visual and the USB connection for controlling the focuser when doing imaging via the laptop.

I think this is getting far too complicated! I may have to rethink this and try to cut it right down and just go manual - maybe a pot to control speed and then a simple forward button and reverse button, or possibly even one button with the pot controlling speed and direction of rotation. This could possibly be controlled with just the motor control board and forget about the arduino.

[themos]

You don't need to add a USB hub if you want an arduino controller to be useable without a computer. Just provide a battery pack (4 NiMH AAA should do it) for the arduino. Or use a DC-DC converter to step down the motor voltage to the 5V the Arduino likes.

[Stargazer33]

Ahh! That sounds like a plan. I have seen a little dc/dc converter on e-bay that should fit nicely into my power distribution box. In fact I believe you suggested it a few posts back! Thanks again themos!

[themos]

It's all clicking into place! I was tempted by the lower-voltage steppers but then I realized that the current requirements were harder, they take a lot more that the half-an-amp that you can use a Darlington array ULN2003 for.  So, better to use a higher-voltage stepper (12V say) with lower current demand and use a step-down 12v-to-5v converter to power the arduino. 

[Stargazer33]

I'm beginning to think that I should have gone for the 12v stepper myself! More shopping on e-bay I feel.

[Stargazer33]

I am trying to stick with the 5v steppers at the moment. I have changed things around a bit and have come up with this layout!

Am I there yet? Or should I take up knitting or something instead?

[themos]

We still need to see a spec sheet for these 5V stepper motors. If they need more than half an Ampere, you can't use the ULN2003.

[Gina]

The driver board supplied with these steppers uses a ULN2003A driver chip.  I'll check the specs and get back to you.

[Gina]

All the info is given here including specs for the stepper motor and how to use it with the Arduino.  I currently have 3 of these running from an Arduino MEGA to control focussing on my scopes or the lenses on my widefield rig.   In the past I've used other Arduino versions including Uno and Nano.  For driving single focusers.

Current drawn by each stepper motor winding is therefore 100mA - 5v into 50 ohms.

[Stargazer33]

Yes the motor comes with a driver board that uses the ULN2003 chip (as per Gina's link) so I guess it should be enough to run the motor.

I was intending to hook it up to an UNO so that I could make use of the USB port to run it from the laptop when doing imaging (this is now a secondary wish as it seems to be getting far too complicated for my simple brain to comprehend!  ).

If it will handle it I may hook it up to the NANO which I bought at the same time. I could then use the UNO for something later on - once I have learnt what I am doing!

I was also hoping to use KCOTARs code as here  I guess I will have to change some parts of it as he has 6 buttons on his control box and I would only have 4. Not that I can tell what his 6 buttons are intended for!?!

[Gina]

Anyone is welcome to use my design of focussing system.  It uses 5 buttons with an analogue connection from warm room to pier.  Any version of Arduino will work with it (the single focuser version) and it uses the mini stepper motor and ULN2003 as mentioned above.  No technical knowledge is required other than connecting 4 outrputs from Arduino to ULN2003 and the ability to solder etc.  The 5 buttons are FastForward, StepForward, StepBackward, 10StepsBackward and FastBackwards.  I guess I should make a new thread with concise details rather than expect others to plough my ramblings in the original thread

[Stargazer33]

Oooh Gina, I could kiss you!   That would be a great help and could possibly save my marriage during my attempt to build a focuser motor drive over the Christmas holiday. 

I will put a decal on the side of the handset stating: "Designed & Supported by Gina from SGL" 

[Gina]

That's lovely - thank you

[Stargazer33]

You're very welcome and thank you! 

[themos]

Gina, have you looked at AccelStepper ? I am thinking of upgrading my design to use this under the hood, it's perfectly useable with the Arduino+ULN2003 combination.

[yesyes]

I've had a look on the web and have found a couple of schematics that I like the look of: KCOTARs one and YESYESs one in his very nice power distribution box.

I'm glad you like my focuser.

Any questions, just ask..

[Gina]

Gina, have you looked at AccelStepper ? I am thinking of upgrading my design to use this under the hood, it's perfectly useable with the Arduino+ULN2003 combination.

Thank you for the link - could bre useful