Memos From the Cube

Developing LUFA has its perks, despite requiring a lot of effort – for one, I get to interact with a lot of people I wouldn’t otherwise, and for another, I get a bunch of free hardware from appreciative users. Fun fact: I’ve been working with AVRs for 4 or so years now, and I’ve only paid for a single board; a Butterfly with a free AVRFreaks tshirt several years ago! Other than small components, solely from hardware donations I’ve amassed a good chunk of the AVR product line, which gives me the freedom to develop lots of interesting things. Sadly, my hardware queue is starting to get a bit long; I’ve got an EVK1101 board, ARM7 board, RZRAVEN kit and a DB101 lying around just waiting for some spare time or a project.

In any case, late last week I got the latest shipment of boards from the newly renamed Micropendous line (from Opendous Inc.) to sample, and once again I’m quite impressed by Matt’s generosity and his design skills. That man pumps out board designs like I pump out lines of code. Unfortunately my boards were manufactured before the name change to the simplified board names, so the pictures here won’t be entirely accurate. Just use your imagination a little .

I’ve numbered them not in the order I’ve received (or Matt has made) them – the order is entirely arbitrary. I’ll go over each board below, giving specs and whatnot. Those familiar with the current line-up can skip to those entries marked as “new”.

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BOARD #1 - Micropendous-4 (NEW)

• AT90USB1287
• 16MHz
• 64KB External SRAM
• 5V-only Operation
• Dual USB connectors for Device/Host mode

This board is the newer version of the older AT90USB647 based Opendous board I received previously, now available as a variation. It improves on the previous design with the largest USB AVR Atmel manufacturers (the 1287) over the smaller 647 AVR microcontroller, doubling the available FLASH and RAM. I’ve heard this is because Atmel doesn’t see much demand for the 647, as customers who need the USB hosts generally need all the RAM they can get at the same time. That’s certainly not a problem on this board, since Matt’s added an external 64KB SRAM chip soldered to the AVR’s hardware external RAM bus:

Which opens up a wide range of interesting possibilities for applications needing lots of RAM like full duplex TCP/IP libraries. Matt’s currently hard at work making an unholy mishmash of LUFA, a modified Arduino core, some bridging code and a third party Bluetooth stack to be the first person to get USB Bluetooth dongles working with the USB AVRs. That’s an ambitious goal, and one that I hope he finishes, as I don’t plan on finishing my own from-scratch Bluetooth stack any time soon (the code currently enumerates the dongle, but I baulked when I saw the amount of work required to just open up a communication channel between devices).

One interesting feature of the larger Micropendous-4 boards is the dual USB sockets – one USB mini socket and one regular USB A socket. This is switched via an on-board hardware jumper, which allows you to plug the mini port into a PC to power the board, while the AVR’s USB pins are rerouted to the USB A socket so that regular USB peripherals can be inserted. This makes host development that much easier for me, as I don’t have to keep digging out a power supply for my USBKEY when I want to develop host applications.

My only concern here is how the SRAM chip affects the number of I/O pins available for general use; if it hogs two full AVR ports and can’t be disabled, it might prove annoying in designs where it is not needed.

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BOARD #2 - Micropendous-2 SD (NEW)

• ATMEGA32U4
• 8MHz
• 3V or 5V Operation
• Onboard micro-SD Card Slot

This is not an entirely new board, rather its a niche version of the existing Micropendous-2 board. It’s essentially identical in every way except for a small micro-card reader mounted on the bottom of the board:

Which is pretty damn cool, if I do say so myself. I’ve already tried out the Card Reader demo in the latest Micropendous SVN revision, but I was left a little disappointed. Currently, the card size is fixed at compile time, rather than dynamically calculated, and the value in the SVN is incorrect for a 1GB card. Still, these are minor issues and ones Matt will be fixing up before his next full package release. Once I corrected these issues I found the reader to be functional, if EXCRUCIATINGLY slow, due to a bug with the SD card library Matt uses, which was fixing the SPI rate to FCPU/64 rather than FCPU/2 after the card is enumerated. Fixing that little bug make the read/write speeds jump up from “impossibly slow” to just “annoyingly slow”, but it’s perfect for on-board data logging or configuration applications.

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BOARD #3 - Micropendous-2 and Micropendous-2 JTAG

• ATMEGA32U4
• 8MHz
• 3V or 5V Operation

Shown here is the original Micropendous-2 board on the far right, with another identical unit on the left save for the mounted JTAG socket. This I thought was interesting – Matt’s gone for the same “micro header + adapter” route that Atmel did for their Raven boards, except he’s reversed the sex of the connectors. On the Atmel Raven, each board has the male header with the adapter sporting a female connector, while on the Micropendous this is reversed. I’ll have to have a play around and see if I like this better; my instinct is that Matt’s system is a slightly better one as the cheap adapter is the more fragile part of the equation than is the board with the actual electronics on it. My only concern is the availability of those tiny headers, but that’s a problem with either method.

Other than that, this is pretty much just a better version of the Micropendous-1 board, with a beefier AVR, and is well worth a look.

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BOARD #4 - Micropendous-Pico (NEW)

• AT90USB162
• 8MHz
• Requires external adapter boards

This new board is a real oddity, and sadly won’t be in general production – so what you see here might well be one of only a couple to ever leave Matt’s evil lair lab. Matt describes it as an attempt to make a super-minimal set of Micropendous boards, which could then be placed into a common set of adapters to ensure a uniform pin-out despite the chosen AVR, using the common subset of AVR pins. It’s a nice idea in theory, with the pico board Matt gave me fitting snugly upside-down (RESET and HWB buttons are mounted on the bottom of the board) into the provided DIL and DIP adapters.

Where this all falls down is the cost of the headers (Matt says this is what killed the design in the end) and the fact that the board’s full potential would not be utilized, as you’d be stuck with potentially only a small subset of the AVR’s I/O pins.

Still, this is a great little curio piece, and I think Matt’s succeeded in making the smallest USB AVR board to date.

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BOARD #5 - Micropendous-4 Variant

• AT90USB647
• 8MHz
• Dual USB connectors for Device/Host mode
• 3V or 5V operation
  

This is simply the Micropendous-4 board listed above, without the external SRAM of the new version and with a 8MHz crystal and AT90USB647 AVR rather than the 16MHz and AT90USB1287 mounted on the newer version. This was, until the latest version, my favourite of all the USB AVRs solely because it made making USB Host applications easier than the USBKEY board, although it lacks the hardware peripherals of the latter like the LEDs and joystick.

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BOARD #6 - Micropendous-Mini

• AT90USB162
• 8MHz
• 3V or 5V operation

This design was Matt’s first revision to the original SIL-layout board, described below, and was basically a design to compete against the DIP form of the Teensy board from PJRC. Sporting micro-sized headers, Matt had it in his head that users would jumper the board to their breadboards or applications. In practice I found the included Mini-to-V1 adapter (converting the Micropendous-Mini to the old SIL layout) more useful, as it allowed me to jam it into my breadboard and not have to worry about a billion fragile wires linking the two. In fact, this is exactly what I used to develop the new AVRISP-MKII clone firmware for the USB AVRs a few weeks ago, and so has proved quite useful.

One thing I’d say about this board is that I’m very glad Matt’s moved away from the tiny, tiny, TINY board RESET and HWB buttons. These are the same buttons that PJRC used on their Teensy board, which I found difficult to press and prone to failure; my friend has managed to trash one of my two Teensy boards through normal use simply because the onboard RESET/HWB button failed after a few weeks use. All of Matt’s other designs (even the Pico) use the same larger, more robust buttons which is a definite plus in their favour.

This board is no longer in production.

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BOARD #7 - Micropendous-1 SIL

• AT90USB162
• 8MHz
• 3V or 5V operation

This is Matt’s original cheap USB AVR board – the catalyst that gave birth to all the subsequent Micropendous boards and the current popularity of the USB AVRs. It’s cheap price ($20) gave hobbyists a great way to experiment with the new USB AVRs for only a little amount of money, rather than sticking with the other AVR models and a USB-Serial converter cable. I found this design quite unusual when I first saw it, due to it’s SIL layout – on the commercial units it mounts vertically into the target breadboard. Pictured here is one I poorly built myself (my first SMT board!) as I’ve sent my other two off to the wilds of the world to give others a chance to test the USB AVRs out.

The SIL layout made this a very compact board for prototyping, except it was quite difficult to remove without bending some of the pins due to all the friction between pins and board. That aside, this was an awesome way to get people started with LUFA and the world of USB AVRs.

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BOARD #8 - Micropendous-1

• AT90USB162
• 8MHz
• 3V or 5V operation

This board is missing from the picture above, as it’s currently sitting in a design I don’t want to remove it from. Basically, it’s the original Micropendous in a DIP layout similar to the other Micropendous boards listed above, only a little smaller. Not as powerful as the other boards – the lack of an on-chip ADC is rather conspicuous – but cheap and great for small hobbyist projects which only need minimal USB capabilities.

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All in all, some very impressive hardware. Congratulations once again to Matt for his great designs!