Memos From the Cube

Next time I’ll be talking about my University robot and a neat curio piece I received yesterday, but for today it’s time to finally keep my promise to myself and review a board I’ve had for a while.

A few months back I received a nice present; an Xbit Electronics Stingray XMEGA development board, fresh from production. I tend to accrue new hardware like a Magpie collects shiny objects, so embarrassingly it has sat on my desk for far longer than I would have liked. Now thanks to my much less hectic schedule I’ve been able to sit down and have a play. Full disclosure applies here: the board was sent to me free, but I have no financial interest in the company making it.

So, first up, a picture. Since despite my last name I am severely lacking in my photographic skills, I’ll instead yank the photo from the official product page here:

Which yields an impressive array of hardware on a medium sized board. I’m actually quite impressed with the production quality of the board I received; the whole thing really does look nice and professional, right down to the clear, sharp silkscreen and oh-so-sexy blue soldermask. When I first saw the board I was immediately stuck by its similar appearance to the Altera DE2 FPGA development kit, which is also a great piece of hardware in my opinion. The Stingray contains all the bits of bobs needed to get up and running, including:

• Buzzer
• Alphanumeric LCD Display
• Eight Switches
• Six 7-Segment LED displays
• Four pushbuttons
• Serial Port (with RS232 level conversion)
• On-Board Programmer
• DC Jack and 9V Battery Supply
• Temperature Sensor
• CAN Bus Translator
• SPI and TWI Temperature Sensors
• Potentiometer
• 8 LEDs
• External EEPROM

And a whole lot more I’m sure I’m forgetting. This makes the board a completely self-contained learners kit for the XMEGA chips, with plenty of functionality built onto the board to make it useful even without any external hardware. And that’s one reason to really like it – I can definitely see schools and Universities picking these up for the classroom use, since they’re just “plug in and go”.

I was rather baffled by the inclusion of the 9V battery header; most 9V batteries aren’t known for their high current output, and there’s a decent amount of hardware on the board. It’s a nice touch, but something I’d find hard to recommend over the USB or DC jacks for board power simply because of the cost of having to keep replacing the battery. The power converter is a switchmode design with presumably high efficiency, so at least the majority of the battery power would go into feeding the board and not wasted as heat, as would be the case with a linear supply.

Most development boards take one of two approaches to programming the processor; either they include an on-board programmer of some type, or they just use a bootloader. Here XBit electronics has done away with the bootloader and taken the former approach, using a USB AVR emulating an AVRISP-MKII to act as an external programmer. And there’s the reason why this nice system is in my possession – if you guessed that the programmer is using my AVRISP-MKII firmware, you’d be absolutely right. I like external programmers since they don’t have the same limitations as bootloaders, don’t carry the same risks of accidental removal, and have a greater software compatibility on the host. Plenty of boards come with weird and wonderful bootloaders that are only supported under one Russian language program downloaded off a BBS that only runs under Windows ME, but this programmer is compatible under AVRStudio 5, avrdude and all other programming software that can talk to Atmel’s AVRISP-MKII programmer.

As for the XMEGA itself, the chip is located prominently in the middle of the board. I’m pleased that the designed picked the ATXMEGA128A1 – the biggest XMEGA currently on the market – for the board, as it means that there isn’t much of a risk of running out of FLASH space in the meantime. The XMEGA128A1 also contains the largest set of on-die peripherals and capabilities, making it really the only choice for an open-ended kit like this. Like the Sparkfun XMEGA breakout board, the XMEGA’s entire pin compliment is routed out to a set of four female headers, so that additional hardware can be attached on an external breadboard if desired. External JTAG and PDI programming and debug headers are routed out on one edge of the board, to make external debugging with an appropriate tool easy.

One criticism; the XMEGA’s main clock crystal is located comparatively far away from the processor itself, due to the female breakout headers. In practice this seems to make no difference to the board, but I’d be interested to know what the implications of this is are as the Arduino Uno’s single crystal design was scrapped due to the trace length between the two processors on the board.

I have a close friend who is interested in Microcontrollers but never tried them, so I’m going to be lending him my Stingray board – the single integrated unit is extremely convenient, and should give him a good starting platform to experiement with. I’m going to be interested to see how he progresses with it.