Category Archives: Arduino

RepRap is Alive!

I’ve been wrenching for a few weeks to machine enough pieces to create a CNC plastic extruder (RepRap / Makerbot). I’ve got the CNC part done, now I have to get the extruder and heated bed up and running so I can start RPing parts.

Sector67 Forum Thread

I’ve gotten a few questions as to what you’re looking at, if you’re completely unfamiliar a visit to Wikipedia should clear things up.

It’s made out of 2″ x 2″ extruded aluminum channel, the railed looking stuff that makes up the top of the arm and the drop for the spindle (dremel) is called 80/20, it’s fairly expensive but is very precise and saves a lot of time for some projects.

The Z axis is the classic over constrained parallel rods, I pulled the rods out of a pair of identical printers and then drilled and reamed to size the end blocks and the slider block, which is just a chunk of delrin plastic. The bad part about using a plastic block for a sliding surface is that you have a drill/ream it over significantly to get it the right size, which in my case just means it’s sloppy and will be replaced by linear bearing when it becomes the weakest link in the machine for precision or stiffness.

The bottom end X-Y axes are THK precision linear bearing. I picked this out of discarded equipment at the university, which I understand it not available to “normal people”. I found out a few years after I picked it up that it’s $0.43/millimeter (yep, that’s a half of a dollar per the thickness of your fingernail, it’s expensive). The bearing carriages are ~$130/each. I was fortunate enough to find a pair of 18″ linear track and a pair of bearings still in their well oiled bags! They do have lash in them and should certainly be run in parallel or with a precision guide track for stiffness/rigidity but for my application (milling light plastics and depositing plastic in an additive process) it’s not a major concern this early in the project.

The other common question is how much does this thing cost. So far I have $199 for the full generation 3 Makerbot electronics (thanks Zach et al., they work great!) and $4.11 for 3 x 1″ long 1/4-20 nuts that are used on each of the axes (True Value). The rest has been collected or given to me by others.

How to Program Sparkfun Arduino Pro Mini

I just picked up a Sparkfun Arduino Pro Mini board for a project.  It’s a really nice really compact board with almost all of the pins broken out on it.  If you already own a Duemilanove you can easily program it using the Arduino software, just pull the Atmega chip off the Duemilanove and then using the shortest side of the board’s contacts, wire:

reset – grn
blank – blk

The words grn and blk are silkscreened on the board to denote which pins are which.  You could of course use a RS232->TLL converter to program this as well, but using the Duemilanove is really convenient as it pulls the reset pin low for you.

On the topic of this Pro Mini board, I had a few e-mails back and forth with Sparkfun trying to figure out what the actual maximum input voltage for the board is, Sparkfun’s Website lists it at 12VDC max, the EagleCAD schematics list it as 16VDC, and the datasheet for the voltage regulator list it as operational maximum 16VDC, with an absolute maximum of +/-20VDC before damage occurs.

Also noted is that the oscillator on this board is absolute crap, I have a timing critical application that I intended to use this board on, using a stopwatch and a Duemilanove and this board, both running identical software and hardware configurations:

15hours 37 minutes elapses, the Duemilanove is exactly in sync with the stopwatch still, the Pro Mini has gained 1 minute and 1 second. I ran this test several more times with identical results, the stop watch and the Duemilanove are in sync, with the Pro Mini gaining time each time, always about 20 second per 5 hours elapsed time, which is not acceptable in my application.

I swapped the Sparkfun crystal/resonator for one of my own resonators and ended up with the same crappy timing. I finally switched out the resonator for a crystal and a pair of capacitors tied to ground and was able to clean up the timing mostly, it’s still gaining a second for every 40 minutes it runs for, it was previously 15 so it’s improved, but not ideal. I’m going to ditch using the Sparkfun board for my own layout on the next iteration.

MAX6675 Thermocouple Amplifier EagleCAD

I created a little SMT board for the MAX6675 thermocouple amplifier in EagleCAD if anyone out there is in need of a board.  It’s very simple layout but it is a bit noisy, definitely expect to average samples coming from this chip (/board?).  Other improvements would be adding a thermistor as the CJC (cold junction compensation) on the board so you can accurately offset the junctions at the board where you break the thermocouple wire and transition over to copper (which creates another TC junction unintentionally so you must compensate for it).

MAX6675 TC Amplifier Board and Schematic

MAX6675 TC Board Schematic and Board (and Panelized)

Windows 7 Hyperterminal Replacement

Well, firstly  a moment of silence for our lost old friend hyperterminal.  But you just want to get serial data flying around again right?  I spent about 30 minutes downloading and finding no free serial port solutions for Windows 7 until I remembered PuTTY!

You can download PuTTY here, and either install it or run the exe.  PuTTY will launch, select

Connection type: Serial

Set your configuration and hit open and you should be in good shape.  You can set up local echo and all of your other preferences through the myriad of menus at the left.  Most importantly you’ll again have a lightweight serial console for Windows 7.

EagleCAD Layout – Arduino Base

If you’re looking for an Arduino basic layout in EagleCAD (all clock/power/ICSP lines run but nothing else) here it is:

Arduino Base Layout

The board layout is troublesome on a single layer board, most of the I/O are currently blocked with power or ground, I’ll leave that up to you to figure out what you want to do.

If you’re looking at this, you’ll probably be really interested in this single sided Arduino layout.