RepRap Funds and Multicopter

Well University has been pretty busy so I haven't been doing much on any projects at home since the last post. I did though, over Easter, have enough time to think up some more ideas. But a few small things before I start on these.

First week back at uni

So I'm back at uni now and this meant orientation week, so this week I have done next to nothing on the printer as I've been too hungover or catching up with people I haven't seen in a while. There are a few things I have had a look into though.

Temperature Sensor, Frame Design and News

Last post I said I would get my thermistor temperature sensor working by the next post (ie this one). I have it working but its not calibrated and thus gives the temperature a few degrees out.

Multiple chip communication and Code documentation

Well once again I've ended up on a forced hiatus. This time its because we're re-roofing part of our house and its taking far longer than thought plus I've ended up with lots of work clumped together so no time to relax in-between. This should finish next week sometime as I'm working constantly until Friday night and then I think I'll be back on the roof again, at least I've ended up with a good tan from it.

Anyway my next goal is to set up SPI communication between two microcontrollers (I just realised I should try three controllers very soon after). In my last post I said I was having trouble with the chip not functioning properly without the programmer attached. I've now fixed that with a 1uF capacitor. What took me so long was that I was unsure about the size as I had previously had a capacitor that was much too big and so didn't do any help. I had a look round and the Atmel documentation seemed to indicate some thing in the range of micro farads but the capacitor used on the Audrino Uno was a 100nF capacitor. As I didn't have any capacitors that size at home I tried a 1uF and it works fine (as in everything functions properly without the programmer attached) so I'll keep that for the time being.

So what I'm aiming for with my test SPI setup is to have a microcontroller with some buttons attached which then communicates to another microcontroller which then drives the stepper motor. In the setup with two microcontrollers, the microcontroller attached to the stepper will then reply with the success or failure as well as some properties of what it did such as how many steps from its original location etc.

I haven't thought about what I will do with the three microcontroller setup as I have only just thought of the idea while writing this post.

There is one problem with SPI other than those mentioned previously (I had a post ages ago when I talked about it) and that is that it is also used to program the device. So to overcome this I'm going to but some detect switches (that is at least what that are called on element14) and connect to some transistors to break the SPI connection when the programmer is plugged in. I won't have this on the final product just for use on the breadboard as the final product should be able to have the SPI disconnected more easily via a cable or similar.

So that is my next step for the electronics side of things. I'm very pleased with how things are going along at the moment other than having to spend so much time not working on the project!

With code, I keep saying I'm going to comment it and make it more readable. I've decided I'm going to use Doxygen for inline commenting and documentation. This is so I use a standard format for commenting but also so I can learn how doxygen works for other programming projects I work on. I've read some basic info online and I've now ordered a book. This is mainly as its easier to have a book to reference than going online all the time and all the information will be in one place. On a side note I've also bought a book on Autotools which means once I get most of the different electrical parts working, I can have the code of the main controller all auto configured and have options when compiling, such as methods of communications for getting the 3D data files to the controller (eg: SD card, USB and ethernet).

Just some quick other things, I'm going to see if I can setup SVN under AVR Studio as this would be a good way of keeping track of revisions of code plus I can use it to sync with code that I've written under OSX. The other thing I wanted to mention was that in the code in the last post, I should have also turned off the start up message on the LCD as when you first turn it on, it doesn't format the text passed too it correctly. The last thing is that I start uni again in just under four weeks so I'll be able to spend more time then thinking about the project.

Exams are over

Well exams are over so my impromptu hiatus has finished. I have actually been doing things since the last post but have not posted due to my exams. So I have given up trying to get programming done on Mac OS X and instead I'm using Windows for the time being while I try to install Arch Linux on my laptop. What is happening under OSX is that the MKII is now connecting and getting the correct driver (well its being supplied correctly and the green light is on for it being the correct driver) but avrdude is not downloading. I tried changing the driver but couldn't get any others to work and I tried changing what I was telling avrdude, as in STK500v2 rather than avrispmkII for example but that didn't fix the problem either. So now I'm using AVR Studio 6 with the hope I'll switch to Arch Linux on my laptop soon (it refuses to boot at the moment so hence why its "I'm trying").

The next thing I have been working on is getting I2C working for my LCD display. This I thought would be easy but is turning out not to be. I have a post on AVR Freaks which I'm using to enquire about how to fix the problem. Once that is sorted I'll write a proper post here about how its done. As I'm actually following that post at the moment, here is a link to the referenced library. I'll have a look after I written this.

In other news, I've got my breakout boards, motor driver chips, breadboard and wiring kit. I'm yet to get solder paste and a hot plate so to do the SMD soldering but I should get the hot plate within the next week and the paste I will probably order from JayCar online as they didn't have any in stock at my local store.

So now my exams are over, I should be able to start designing the structure and once I have the LCD display working I will start to play with the two chips for motor control. But for now, I'm going to the pub to celebrate end of exams!

More structual ideas and some basic electronics

So I've been too busy with uni (my damn uni exam are in three weeks), so have felt guilty about starting to design things in inventor so tonight decided to jot down a slightly more detailed designed compared to the previous sketch.

Yesterday I also asked one of the lab techs at uni about an issue I had previously stated about controlling the steppers with a slave controller or not. He said that he had done both previously and said that it really depends on the grunt of the master controller, as it should be doing error management on top of just the control. So with that in mind I think I'll use slave controllers to manage the steppers. Talking of which another conundrum I've come up with is how to operate the Z plane. I've decided telescoping is too complex and would also be more flimsy compared to moving the entire frame. This has made me think how many steppers to use for the Z direction. If I have two it means that at any point in time one of the other two plane could be on an angle which would be bad. I'm thinking I will probably just use two motors and make the frame more rigid by how its mounted onto the pylons in the corners, maybe having a second join on the Z slide round the back of the pylons, though this would make it slightly harder to mount a case. This is also a problem as the weight from the XY steppers will mean there is more force in certain places compared to others. The stepper motors are only around $20AUD so maybe its better having three Z steppers as it might be cheaper all up. Another issue I had raised previously was the weight of the ball screws. I've decided these aren't a problem as they won't weigh much relatively and other materials will most likely deteriorate quicker.

One last thing was that I had a quick look at development boards for the electronics today on element14 (Farnell) and I'm thinking either the Texas Instruments: TMDXDOCKH52C1 - H52C1 Concerto Experimenter Kit or FreeScale Semiconductor: FRDM-KL25Z - FreeScale Freedom Board. Most of the others they had on offer were much more like a computer on a board rather than basic development boards. I think I'll start off with one of these and get a feel for how they work and then if needs be design my own board. I haven't looked into the slave controllers but I'm thinking of using either TI MSP430s, Atmel ATmegas or a Microchip PIC. The TI MSP430s I have at the moment seem to not work as well as they are made out to, even when simply copying example code so I will most likely use one of the other two.