nippe.teknopapu.net

As some who hang out at #arduino@ircnet may remember, I was trying to generate VGA signals with Duemilanove board a while back. Then I stumbled across AVGA library by  Jaromir Dvorak, and thought I could use it as a starting point. However, AVGA is designed to run on faster clock than Arduino and because of that some of the code needs to be modified, but not much. Ok, that doesn’t sound too bad, but another issue arises – AVGA has some assembly code put in to a .S file, and we all know that Arduino IDE doesn’t like them. There is a workaround for this – you could compile the assembler file by hand and add it as a object file to your build or you could do like I did, ditch the Arduino IDE along with the libraries and use avr-gcc to compile and avrdude to program. Of course you can use any AVR compatible toolchain here, the AVGA source has an example project for AVR Studio.

Hello world! AVGA on Arduino @ 16MHz

(continue reading…)

Today at work, during a coffee break of course, we were tossing around ideas about how to control guitar effects with accelerometer – like doing a whammy dive-bomb by doing a motion with guitar. Of course that would need the accelerometer to be built in to the instrument itself, but that’s not a problem. But where to find a suitable effects processor that a) has all necessary effects and b) has suitable input capabilities to accept external control of the effects? It turned out that I have a suitable device already!

Years ago I bought a Digitech RP50 effect processor for guitar. It’s not very good piece of gear but it has worked for me while practicing at home, and even during some home studio sessions. The nice thing about the RP50 is that it has a 6,3mm jack labeled Control In in the back. The user manual says that one can hook up a passive volume pedal to it and use it to control master volume, wah or whammy effects on the processor. Nice. Now, how can I emulate a passive volume pedal with Arduino?

(continue reading…)

While digging through my pile of hardware I found a LCD display made by Epson. I’ve salvaged it from somewhere ages ago and decided to see if it works. After a little bit of google fun I found enough info about it in order to get it running with my Arduino. The display is Epson EA-D20025AR and it is Hitachi HD44780 compatible, but there’s a catch. The connector is only 14 pins and it’s wired differently than you would first think. The small marker on that 14-pin connector that usually marks pin 1 is used to mark pin 2 in this case. I found out that there has been lots of questions about this particular display, so look no further – here’s the pinout for it:

Pinout for EA-D20025AR

(continue reading…)

Yeah! I just got the stepper and gearing for Y-axis to work. The current setup seems to achieve even better precision than the X-axis I tested previously – we’re talking something like 900dpi – which is an estimate at this time. I use Mitsumi M42SP-7 stepper from Canon BJ200EX printer running on 12V and the gearing is customized from the aforementioned printer and Canon D1250U2 flatbed scanner. No pictures this time though :P

Next on my list is to make the X-Y table so I can start testing and calibrating it. When I get that done, I’ll move on to the Z-axis. It is going to be the most tricky part, and I suspect it’s not going to be as precise as the other two. I’ll probably need to build the whole mechanics from scratch if I cannot find suitable drive belt for it.

On other stuff, I finally received some PWM ICs from Texas Instruments for my moodlight project. The chips include 24-channel 12bit PWM, which is ideal for the RGB setup. Too bad it’s in HTSSOP32 package so I need to make a small PCB in order to mount it on my prototyping board, lets hope I can find time to make that at work :)

Shit, I just found a bug in my GCode interpreter, the Y-axis drive is not working as intented through ReplicatorG. Oh well, it seems to be only a misconfiguration on my behalf. Off to fix that.

I was having a slow sunday with a hint of hangover while I remembered that I have an old flatbed scanner stashed in my closet. After some digging I found it and immediately took it apart. Pretty simple design, with a Mitsumi stepper motor. That gave me an idea to make a x-y plotter with it. I’m still hunting for some more parts but should get some old printers this week that will donate their internals to my next creation and then it’s just fabricating and coding.

The motor, Mitsumi M35SP-7N, has 48 steps in full 360 degrees rotation and runs nicely on 5V, though it can’t run very fast. But that doesn’t matter at this point :)

Testing...

After I extracted a driver chip (ULN2003A) from the scanner’s PCB I was ready to hook it up to my Arduino and run some tests. It appears that with the scanner mechanics in place, the scanner bar achieves about 600dpi precision, which should be good enough for my needs. There is a small issue though. Since the bar is driven only from one end, there is slack in the movements of the bar – especially on the end that doesn’t have the drive belt attached. This slack is visible to eye and it will cause problems in the future when there’s weight from another driving mechanism on top of it, so I’m trying to locate a similar scanner (Mustek 1200CP) and take another driving mechanism from it for the other end of the bar.

The testing software I’m using is just a simple implementation of stepper class found in Arduino examples, MotorKnob example to be precise. For the final software, I’m planning on using slightly modified GCode interpreter from RepRap project. The modifications are due to my motor driving circuitry that differs a lot from the RepRap, which has more advanced and better driving capabilities than the setup that I have here at this time.

Stay tuned for future updates on this :)