Repetier Firmware Now Runs on Printrboard

I spent this past weekend porting Repetier-Firmware to Printrboard and Teensyduino. It took me a while to get it working properly, because the code intermixes calls to fastio and Arduino, and the pin definitions in fastio.h were different from the Teensyduino Arduino library. It is now working pretty well, so Printrboard and Teensylu users now have yet another option for RepRap firmware. I’ve already submitted my changes to Repetier, and he’s merged them into his code. Download it here: https://github.com/repetier/Repetier-Firmware.

In case you haven’t tried it, Repetier also has an interesting host program, Repetier-Host, which works with other firmwares as well as Repetier-Firmware.

Ktone Travel Electric Guitar Review

I’ve been looking for a compact guitar to take with me on road trips, camping, and to play when I’m killing time waiting for my kids at their various lessons in my car. After much research on the Internet, I narrowed it down to either the Washburn Rover or the Hofner Shorty. The Rover looks like a great buy at $125. It gets great reviews, and comes with a very nice soft shell case. For $119, the Shorty, on the other hand, only comes with a cheap gig bag. I was really itching to get the Rover, but after pondering it for a long time, decided that an electric guitar was more appropriate because: 1) it will hold up better in heat/cold/humidity sitting in my car on road trips and 2) it can be played silently in hotel rooms without bothering the rest of the family.

While searching for a good price on the Hofner Shorty, I came across a much cheaper knockoff on eBay – the Ktone Travel Electric Guitar. It looks so identical to the Shorty that many people have hypothesized that they’re made in the same factory. At $69.99 including shipping, it’s $50 cheaper than the Shorty – so much cheaper that my interest was piqued. The Ktone got good reviews at Ultimate-Guitar and some other discussion sites. It turns out that there are several clones of the Shorty in the wild, if you search long enough.

Planet-Z posted a scathing review of the Ktone, complete with photos and a video. The guitar that .. reviewed was a disaster, with loose/unusable tone pot, mismatched wood on the neck, and terrible fretwork.That put me off so much that I was ready to buy a real Hofner Shorty, until I read a comment on the Planet-Z review from someone who bought a real Hofner Shorty, and found it to also be of bad quality. Unfortunately, none of the stores near me have Shortys for me to try out, so I decided to just take the plunge and try the Ktone first, since it has a 30 day money back guarantee (minus shipping charges).

I bought the Ktone Travel Electric Guitar from eBay seller kukufashion. Interestingly, my Paypal receipt showed the recipient as none other than Ktone Corp.!

The guitar comes with a crappy gig bag that looks identical to the Shorty’s and a crappy guitar cable that’s basically a thowaway.

When first opened up the package, I had mixed feelings. The color was metallic blue like the Shorty, unlike the baby blue pictured in the eBay listing. The neck on mine didn’t have an awful looking join @ the headstock like the one that Planet-Z got. Instead, it had some strange colored grain at the other end, and what looks like melted polyurethane. The strange grain is actually growing on me.. kind of like curly maple.

The body’s finish looked decent, and the controls were all installed properly and had smooth action. Thankfully, mine didn’t have the poorly seated frets with sharp ends like Planet-Z’s copy, but although it’s playable, the frets are in dire need of leveling and polishing. The guitar looks like a Hofner Shorty factory reject. Except for the body, the finish work is horrible. The back of the neck has sanding marks, there are various dents and scrapes all over the place, and even the bridge has cosmetic defects. However, I was thinking most of the defects were cosmetic, and what do you expect for $70?

I tuned it up and plugged it in to my amp. The first thing I noticed was that the guitar cable wasn’t clicking in properly to the output jack. It worked fine, but the cable could get tugged out too easily.

The output jack felt like it wasn’t engaging my guitar cable properly, so I took it out to have a look. Amazing… they used such a low grade connector that it didn’t even engage properly with the groove in the 1/4″ TRS plug.
(Notice the extremely thin wiring). OK, not a big deal, and I can always replace the jack easily and cheaply.

The setup of the guitar was terrible, but I’m used to that, even with fancy guitars, so I thought it wasn’t a big deal. The first thing I did was check the neck relief. It wasn’t too bad, so I didn’t adjust the truss rod. Next, I lowered the action. The bridge has so much wiggle in it, and the screws were already screwed in so far that I almost ran out of adjustment lowering the action. Luckily, I was able to get it to a comfortable playing height when I lowered it down to its limit. Not a good sign. I can lower it a bit more by shimming the tailpiece. The slots in the bolts are too big, so the whole bridge/tailpiece tilts up a bit. The frets on the low E and A string need to be leveled a bit past the 14th fret.. there is a lot of buzz there, so I had to raise the action slightly to compensate.

It wasn’t until I started trying to adjust the intonation that I found out what a disaster the guitar really is. The intonation on the low E string was a full 12 cents sharp! No wonder the guitar was impossible to tune! I’ve never gotten a guitar with intonation that far off. First, I tried to adjust the low E string’s saddle, but even when I adjusted it as long as it would go, it was still 12 cents sharp! I was thinking that it was time to pack it up to return to Ktone but then I realized that there are also screws that move the whole bridge backwards. After fiddling with the screws and test the intonation over and over, I finally got it into decent adjustment .. just barely.. to get the low E intonation correct, I had to set the strings to the maximum length.. both the saddle adjustment screw and the tailpiece adjustment screw maxed out. My adjustments lengthened the string by …” Whoever designed the guitar didn’t measure the length of the strings properly. Unfortunately, with the tailpiece adjusted to maximum string length, the G string’s intonation goes flat by 6 cents even when its saddle is adjusted to minimum length. I can’t adjust the tailpiece, because then the low E will go sharp. If I could flip the saddle around, like they way the top 3 strings are, I could shorten the string some more, but the saddle pieces aren’t removable. I am just going to have to live with the G string 6 cents off. Or I could split the difference by making the A & E strings a bit sharp.

One thing that also signals that something is wrong is that the harmonic @ the 12th fret occurs not exactly on top of the 12th fret, but a few mm past it. Something is definitely wrong w/ the positions of the frets on the neck. Despite these issues, after my 2hrs of adjusting the intonation, it sounds a lot better. While the intonation isn’t perfect, it’s acceptable to my ears, especially for a cheap guitar that I’m going to be tossing in the car and taking to the beach. It’s inexpensive enough that I’m not going to cry if it gets stolen or damaged.

After playing with the tuning for a while, I found that the guitar always sounded out of tune, even when I used my Peterson Strobotuner. Something must be wrong with the intonation, I thought.

The single bridge humbucking pickup is pedestrian. It’s not very hot, and the tone is a bit thin, but I was surprised how much effect the tone knob has … makes sound passable. I’ll probably replace it with something better in the future, if I can tolerate the guitar.

The gig bag is cheap, but it doesn’t look any worse than the one that comes with the Shorty. What I hate about gig bags, is that they don’t protect the tuners, so the tuning is always way off when you take the guitar out to play.

So at $69.99 is the Ktone Travel Electric Guitar a good buy? Just barely. If I didn’t have to pay 2-way shipping to return it, I probably would have just returned it. Even if the Shorty has issues, there’s no way that it could possibly be as shoddily built as the Ktone.

Anyway, it serves the purpose I bought it for… a small, light, portable guitar that I can take everwhere and not have to worry about getting ruined or stolen. But I think you should avoid this piece of shit like the plague!

Running Marlin Firmware on a Printrboard

As of this writing, the official version of Marlin firmware from github does not yet work with Printrboard.  Printrboard is a fork of Teensylu, designed by the folks at Printrbot. Printrboard isn’t yet available for purchase, but since the design is open source, anyone can download it and get the PCB’s manufactured themselves. Sprinter is currently the only RepRap firmware works with Teensylu and Printrboard out of the box.  I am now successfuly running Marlin on my Printrboard.  Below is a video of Printrboard virtually printing a Printrbot with Marlin:

Last month, I submitted an issue with ErikZalm to get the compile errors fixed when compiling Marlin for Teensylu.  The main branch of Marlin now compiles for Teensylu by setting MOTHERBOARD = 8.  Unfortunately, this build setting won’t work with Printrboard, because some of the pins are different.  Also, there is a kill function that Marlin calls if it detects certain things like a shorted thermistor, etc… but it’s not able to send the error messages back to the host, so it looks like your board is just dead.
I think Erik is too busy right now getting V1 out the door to deal with making fixes for a couple of not so popular boards, so I’ve forked Marlin on github with my fixes for making it behave nicely with Teensylu and Printrboard.  You can download it here:  lincomatic/Marlin.
——————————–
For Firmware Hackers Only
For those who want to know what’s special about my branch of Marlin, it has to do with the mappings of the I/O pins.  The code in Marlin has two different ways to access digital I/O pins: 1) the Arduino digitalRead/Write() functions 2) fastio – there are macros and pin assignments in fastio.h.  In ErikZalm’s Marlin branch, the pin numbers are different between Arduino and fastio functions, which leads to confusion and bugs.  What I have done is use the digital pin definitions in Teensyduino’s core_pins.h and updated the pins in fastio.h to match them.  This way, a call to digitalRead(28) is equivalent to _READ(28).
EXECEPTIONS:
  1. in pins.h, analog pins use ADC numbering instead of digital pin numbering.  Therefore, even though B_THERM -> F0/ADC0 and E_THERM -> F1/ADC1, we are using them as ADC pins, so B_THERM=0 (ADC0) and E_THERM=1 (ADC1).
  2. Printrboard uses some pins that aren’t supported by Teensyduino, since they aren’t exposed in the Teensy hardware.  Therefore, those pins aren’t listed in core_pins.h.  I have added them to fastio.h, so they are accessible only with fastio macros.  They are digital pins 46 and 47 see the “//– Begin not supported by Teensyduino
    ” section of fastio.h

EXAMPLES:

XSTEP = physical pin 51. Looking at the AT90USB1286 spec sheet, pin 51 = PA0 (AD0)
in core_pins.h, #define PIN_A0 28
in fastio.h,

#define DIO28_PIN PINA0
#define DIO28_RPORT PINA
#define DIO28_WPORT PORTA
#define DIO28_PWM NULL
#define DIO28_DDR DDRA

so in pins.h, X_STEP = 28

X_MIN = AT90USB1286 pin 9 = PE3
core_pins.h doesn’t have a definition for PIN_E3, because the pin isn’t accessible in Teensy++, so we can’t talk to that pin at all with the Arduino functions.  However, it’s in fastio.h:

//– Begin not supported by Teensyduino
//– don’t use Arduino functions on these pins pinMode/digitalWrite/etc
#define DIO47_PIN PINE3
#define DIO47_RPORT PINE
#define DIO47_WPORT PORTE
#define DIO47_PWM NULL
#define DIO47_DDR DDRE

so X_MIN = 47

How to Program an AT90USB1286/Teensylu/Printrboard with Arduino and USBtinyISP

My first step in loading Marlin RepRap firmware into the Printrboard is to get Arduino to play nicely with it.  The method I am going to describe in this article for programming a Printrboard with Arduino will work with the Teensylu or any other device that uses the AT90USB1286 and has an ICSP connector.   The programmer we are going to use is a USBtinyISP or compatible. Since the AT90USB1286 isn’t officially supported by Arduino, it takes a bit of setting up to get things working properly.

I first looked at the instructions on Teensylu’s page in the RepRap wiki, but found them very confusing, and I didn’t like the idea of having to send the HEX file to the MCU using an external utility instead of doing everything within the Arduino IDE. So, I set out to streamline the process and document it as I went.  If you follow my method below, you’ll be able to compile and download your firmware all within the Arduino IDE.

Step 1: Download and install Teensyduino

Teensyduino was created by PJRC for their Teensy line of boards.  Teensy is a great alternative to Arduino if you want an ultra compact board with built in USB.  The Teensy++ happens to also use the AT90USB1286, so it’s compatible w/ Printrboard/Teensylu.  Follow PJRC’s instructions for installation from the download link.

If you only plan to program for RepRap, you don’t need to install any of the libraries.  On Windows, you will be prompted to install the serial driver. Select yes.  You don’t have to worry when Windows complains that the driver is unsigned… it’s just an INF file to tell Windows to use one of its own built-in drivers.

Step 2: Modify Teensyduino Configuration for use with USBtinyISP

Download at90usb1286txt.zip.

Navigate to where your Arduino files are located.  On my computer, I have them in d:\arduino-0022.  We will call this <arduinofolder>.  Now, find the subfolder where the Teensyduino library was installed:

<arduinofolder>\hardware\teensy

If you are in the correct folder, you should already see a boards.txt and a subfolder called core in there.  Drop the files from at90usb1286txt.zip into that folder, overwriting the existing boards.txt.  You should see something like this:

If you don’t plan to develop with any of PJRC’s Teensy or Teensy++ boards, you can keep them from showing up in your Arduino menu by copying boards.txt.nopjrc over boards.txt.

Now, when you start Arduino, you should see some new configurations in the Tools->Board menu.  The important ones are:

[usbtinyisp]AT90USB1286
[usbtinyisp]Teensylu/Printrboard
[BootloaderCDC]AT90USB1286
[BootloaderCDC]Teensylu/Printrboard

To use a USBtinyISP programmer, select either [usbtinyisp]AT90USB1286 or [usbtinyisp]Teensylu/Printrboard. The only difference between the two configurations is that I took the extra useless options out to make things simpler when programming Teensylu/Printrboard.  The Teensylu/Printrboard option is the same as the AT90USB1286 option with USB Type = Serial and CPU Speed = 16MHz.

At this point, you can plug in your USBtinyISP and into your AT90USB1286/Teensylu/Printrboard and start programming!

So what are the [BootloaderCDC] configurations for?  They allow you to download sketches into your target board directly through a USB connection to your host, without the USBtinyISP programmer.  See my next article for details on how to do that.

Update 20140909: I have uploaded a copy of Arduino 1.0.5-r2 for Windows to github, which is already modified to work with the AT90usb1286, so you don’t have to modify it as above. Simply go to https://github.com/lincomatic/arduino-1.0.5-r2-at90usb1286 and click the Download Zip button, and then extract the contents to your PC. My distribution also supports the USBasp in addition to the USBtinyISP.

RepRap – 3D Printing Project Kickoff – Printrboard First Look

I have been somewhat intrigued by the RepRap project, an open source 3D printer movement, for several years.  However, wasn’t motivated enough to jump into the fray until late last year, when I saw Brook Drumm’s Printrbot on Kickstarter.

With only about 1 hour left before funding closed, I pledged $500 to get a Printrbot kit. While I could have started from scratch, and built a Prusa Mendel, after reading about how much tweaking is involved in building and setting up a RepRap, I decided to start with a Printrbot – a cute, compact, and simple design, and the most inexpensive RepRap at the time.  Printrbot’s Kickstarter was a smashing success.  They raised an astonishing $830K. Unfortunately, the gigantic amount of orders they received means that mine will take a little longer to get to me than I originally anticipated. So, I’ve been immersing myself in the intricacies of the electronics, firmware, host software, and mechanical aspects of RepRap for the past couple of months.

There are a variety of popular controller electronics for RepRap, the most popular being RAMPS.  The electronics are one of the largest costs of building a RepRap.  Although RAMPS is convenient, because it’s based on an Arduino Mega, I like the idea of having a single dedicated board.  The Printrbot folks have designed their own controller board, which they call Printrboard.  Although Printrbot is not yet selling Printrboards, the design is open source, and thus, I was able to obtain one before their release.

Kang, a fellow RepRapper from Seoul, Korea, built a few Printrboards and sent me one to play with.

Printrboard is a fork of Teensylu, an AT90USB1286/AT90USB1287 based RepRap controller.  I like the fact that these boards are based on the AT90USB128x MCU’s because they have built-in full USB support, eliminating the need for an external serial->USB bridge IC; additionally, the native USB support means that communication with the host computer is blazingly fast – 12Mbps rather than 115200kbps.

There are a few notable differences between Printrboard and Teensylu.  Printrboard is a single board solution.  First, Printrboard adds an integrated SD card reader.  This is handy for printing while untethered to a computer.  Teensylu has I/O pins which can be used to easily add an SD card reader.

Second, the stepper motor drivers are integrated onto Printrboard’s PCB, while Teensylu uses plug-in Pololu/Stepstick carriers.  The advantages of integrating the stepper drivers onto the main PCB are reduced cost and compactness.  The downside is that it is not uncommon to blow up a stepper driver IC, so having them soldered in means if one goes bad, the whole board is unusable.

Third, Printrboard uses Allegro A4982’s in a 24-TSSOP package, while Pololu/Stepstick use the Allegro A4988 in a 28QFN package.  The TSSOP package is considerably larger, and has a wider pin pitch, which makes reworking the board easier if one of them blows out; the 28QFN is very tiny and not for the faint of heart.  The other difference between the A4982 and A4988 is that the A4982 only supports full/half/quarter/sixteenth stepping, while the A4988 also supports one eighth stepping.

Some other minor differences between Printrboard and Teensylu are that while Printrboard only supports a 12V2 ATX power input, Teensylu gives more power options.  Also, Teensylu has a large USB-A socket, while Printrboard uses a micro USB-B socket.

I am diving into figuring out how to load Marlin RepRap firmware into Printrboard/Teensylu, to keep my end of the bargain with Kang.  A series of articles will follow with my findings.

OpenEVSE – Open Source J1772 EVSE (“Charging Station”) for Electric Vehicles

Last year, I purchased a Nissan Leaf, which is an all electric vehicle (EV). Although the Leaf comes with an included L1 EVSE (“trickle charger”), which connects to a regular 120V wall outlet, it takes way too long to charge the car. The more practical solution is to purchase and install a J1772 L2 EVSE which is equivalent to the commercial charging stations you see in public parking lots. The problem is the cost. J1772 L2 EVSE’s cost a couple of thousand dollars; the quote I got from Aerovironment, Nissan’s chosen installer was about $4000 including installation. Considering that modern EV’s using the J1772 standard have the charger built-in to the car, and that a J1772 EVSE is no more than a smart safety interlock plug for connecting the car to the wall, I thought the cost was pretty outrageous.

I obtained a copy of the SAE J1772-2010 standard, and after a few hours of perusing it, realized that a J1772 EVSE could be implemented with an Arduino, a few parts, and a relay at the fraction of the cost of the commercial products.  Furthermore, that the circuitry is so simple and compact that it could be built into a small case that fits into your hand, and can easily be thrown into your trunk, rather than the giant monstrosities like GE’s WattStation.

I started to design my own EVSE around an AVR MCU, but soon discovered that Chris Howell had had exactly the same idea, and posted about his Weekend EVSE project on the MyNissanLeaf forums.  Chris had already made major progress on the project, so I thought, why reinvent the wheel?  I contacted Chris, and we decided to team up to develop an inexpensive, portable L1/L2 J1772 EVSE. Chris is a wizard with PCB layout, and has shrunken the board down to smaller than an Arduino over several revisions. It’s truly a sight to behold how tiny and simple it is after seeing the giant messy hackorama that’s being funded by the DOE, the $5000 Blink EVSE, which is just an amalgam of OFF THE SHELF DEVICES IN THEIR ORIGINAL CASES: http://www.mynissanleaf.com/viewtopic.php?f=26&t=5664 . One thing that I find annoying about commercial EVSE’s is that they often waste too much power in standby mode. Nissan’s included EVSE draws about 3W in standby, which doesn’t sound like much, but the question is WHY? Vampire power wastes about 10% of the energy used by a typical residential household. I’ve heard that the Blink wastes more than 50W when it’s doing nothing. Not only that, many of the commercial offerings (including Nissan’s included L1 EVSE) aren’t even 100% J1772 compliant!

After many hours of tweaking and testing, we designed a 100% J1772 compliant dual mode L1/L2 EVSE.
This DIY EVSE has worked flawlessly charging my Leaf ever since last summer:

The actual EVSE logic board is the tiny PCB at the top with the 3 LED’s attached to it.  The switching power supply is on the bottom right, and a 30A relay is on the bottom left.  A CT in the upper right is used to detect ground faults.

For a portable unit to throw in my trunk, I need adjustable current, so I’ve implemented a 1-button menu interface using a common HD44780-compatible 16×2 LCD, connected to an Adafruit LCD backpack, which greatly reduces the pin count required for interfacing to it. I’m currently using it in i2c mode.

Note how small the controller PCB is now … Chris is a PCB layout ninja … yes, that’s a complete implementation of a J1772 EVSE on that tiny board.  Now, go back to the Blink EVSE link I listed above, and see how huge and complex the circuits are in the commercial offerings THAT AREN’T EVEN 100% compliant to the standard!

This time, instead of going into the expensive box I bought for the first EVSE, it’s going to live in a $5 NEMA wiring box from my local hardware store. I think this box will be a lot more durable against getting dropped and thrown around than my fancy $18 NEMA box.

Hardware hackers, what are you waiting for?  Join in on the fun.  We’ve open sourced the design as OpenEVSE:  http://code.google.com/p/open-evse/. Now, you can build your own fully hackable, customizable EVSE!

DISCLAIMER:  Don’t jump into this project unless you have a thorough understanding of the precautions which must be taken when dealing with high voltages and currents.  It’s quite easy to electrocute yourself and DIE if you don’t know what you’re doing.

AVR CAN Bus Project: Step 4 – LeafCAN: Nissan Leaf SOC Meter

I have implemented a SOC (State of Charge) meter for the Nissan Leaf. Many thanks to garygid and others from the MyNissanLeaf forums, for their help in decoding the Leaf CAN bus messages, and figuring out the pinouts.

The top line shows the SOC%, raw SOC value, and number of charge bars displayed in the dash.
The second line shows battery pack voltage and current in amps.

You can download the Eagle CAD schematic and AVR (Arduino) code from github:  lincomatic / LeafCAN
The Eagle schematic uses the Sparkfun library.

The schematic shows how to implement the entire circuit, without using the Olimex AT90CAN128 breakout board.

My original intent was to make a small PCB that directly attached to the LCD, and put it into a small case, but I never got it past the breadboard stage.  Unfortunately, I have gotten busy with other projects, so I am probably not going to do further development on this device nor finish the PCB layout, unless there is a large amount of interest. However, feel free to adapt it as you wish for your own CAN bus projects. Do bear in mind, however, that the design is licensed via the GPL, so if you use it for a commercial project, you must openly share your design.

Previous: AVR CAN Bus Project – Step 3: CANspy CAN Bus Monitor
Next: LeafCAN v1.1 Released

AVR CAN Bus Project – Step 3: CANspy CAN Bus Monitor

Sorry for the delay in posting the circuit and schematics from my AVR CAN Bus Project – Status Update 1.  The circuit for interfacing the Olimex AT90CAN128 Header Board is incredibly simple, and only requires 3 components.

Parts List
(1) .1uF ceramic capacitor
(1) 10K resistor
(1) Microchip MCP2551 CAN transceiver

Schematic

If you’re going to connect it to a Nissan Leaf, the car has 3 different CAN buses accessible via the OBD-II connector. The pinouts can be found on MyNissanLeaf.com in this thread: Leaf CANbus Decoding (Open Discussion)

To communicate with the AT90CAN128 header board from my PC, I connected a USB to serial converter to USART0: TXD0 (pin 3) and RXD0 (pin 2).

Arduino Sketch

Below is my CANSpy sketch for monitoring the CAN bus via the serial port, as depicted in my Status Update 1.

Download: CANspy.zip

To compile the sketch, follow the instructions in AVR CAN Bus Project – Step 1: Programming AT90CAN128 with Arduino.

In my next update, I’ll show how to implement a SOC (State of Charge) meter for the Leaf using a LCD display.
Previous: AVR CAN Bus Project – Status Update 1
Next: AVR CAN Bus Project: Step 4 – Nissan Leaf SOC Meter

AVR CAN Bus Project – Status Update 1

I got the circuit wired up yesterday:

The 6-pin jumper on the left lets me select one of the 3 CAN buses on the Nissan Leaf accessible via the OBD-II connector.

I hacked up some code quickly, and was pleasantly surprised that it actually worked! Woohoo! The part I thought was going to be most difficult – getting the CAN interface firmware working – turned out to be the easiest. Here’s my first capture of live data from the EV CAN bus:

Schematic and source code will follow.

Previous: AVR CAN Bus Project – Step 2: Programming Low Fuse
Next: AVR CAN Bus Project – Step 3: CANSpy CAN Bus Monitor

AVR CAN Bus Project – Step 2: Programming Low Fuse

One of the basic functions that the CAN Bus project needs is to be able to communicate with a PC via a serial port.  For modern PC’s the most straightforward way is to connect the AT90CAN128 header board to the host via a Serial->USB converter.  The most common type is the ubiquitous FTDI Cable, which is a USB cable with an embedded FT232R chip inside. Since I have a couple of spare Arduinos, I like to just use the embedded FT232R in the Arduino, rather than investing in a FTDI cable.  To use an Arduino as a serial cable, simply remove the ATmega328P MCU, and then connect the the TxD, RxD, and GND pins between the Arduino and the external device.

The AT90CAN128 has two USART’s.  The first one, on pins RXD0(2) and TXD0(3), is accessed via the Serial object in Arduino.  The second one, on pins RXD1(27) and TXD1(28), is accessed via the Serial1 object in Arduino.

To test serial communications with the host PC, I connected the first USART to the Arduino board with MCU removed as follows:

AT90CAN128 RXD0 pin 2 -> Arduino Digital 0 (RX)
AT90CAN128 TXD0 pin 3 -> Arduino Digital 1 (TX)
AT90CAN128 GND pin 53 -> Arduino GND

Then I wrote a quick sketch to simply read characters from USART0 and echo them back to the PC:

void setup()
{
Serial.begin(38400);
}

void loop()
{
while (Serial.available()) {
int c = Serial.read();
Serial.write(c);
}

To instead test the 2nd USART, substitute RXD1 for RXD0, TXD1 for TXD0, and Serial1 for Serial.

After burning the sketch, I simply opened the Arduino Serial Monitor, and typed characters to test the connection.  Much to my chagrin, the AT90CAN128 was echoing garbage back to the host.  I spent hours trying various things, checking and rechecking my wiring, to no avail.  I started to suspect that maybe the at90can files I got from SuperCow were inproperly configured.  One thing that raised this suspicion is that I found that the delay() function was running much slower than it should.  User evnow of the MyNissanLeaf forum pointed me to a HEX file of a similar serial echo program that Olimex posted on their site for the AVR-CAN board.  I burned the file into the AT90CAN128 using avrdude:

avrdude -c usbtiny -p at90can128 -U flash:w:avr-can_UART.hex

Once again, the board was corrupting the serial data.  This test showed that the culprit probably wasn’t SuperCow’s at90can files, since this hex file has been tested and working by other users.

Finally, it dawned on me that perhaps the fuses weren’t properly programmed.  I got a crash course on fuses from Adafruit’s avrdude tutorial.  Adfruit’s tutorial also linked to a great AVR fuse calculator.  First, I read out the fuses to 3 files:

avrdude -c usbtiny -p at90can128 -U lfuse:r:lfuse:h
avrdude -c usbtiny -p at90can128 -U hfuse:r:hfuse:h
avrdude -c usbtiny -p at90can128 -U efuse:r:efuse:h

The 3 commands above read the low, high, and extended fuses respectively, and output them as text files lfuse, hfuse, and efuse.  I found that the values were lfuse=0x4f, hfuse=0x19, efuse=0xff.  Using the Embedded Atmel AVR Fuse Calculator, I noticed that when lfuse=0x4f, that CKDIV8 (Clock divide by 8)  is enabled.  This didn’t seem right, and might account for the fact that the delay() function seemed to be running about 8x too slow.  Not knowing much about fuses, I decided to just use the value that Arduino uses for the ATmega328P, lfuse=0xFF, which turns off CKDIV8.

avrdude -c usbtiny -p at90can128 -U lfuse:w:0xFF:m

Bingo!  No more corrupted serial data, and the delay() function now runs at normal speed.  I have a feeling I’ll have to play with the other fuse bits at a later date, but since the board is working OK I’ll leave them be for now.  If you want to copy all of my current fuse settings, use this command:

avrdude -c usbtiny -p at90can128 -U lfuse:w:0xFF:m -Uhfuse:w:0x1F:m -U efuse:w:0xFF:m

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