Hackaday Prize Entry: A Cheap STM32 Dev Board

Dev boards sporting a powerful ARM microcontroller are the future, despite what a gaggle of Arduino clones from China will tell you. Being the future doesn’t mean there’s not plenty of these boards around, though. The LeafLabs Maple has been around since 2009, and is a fine board if you want all that Processing/Wiring/Arduino goodies in a in an ARM dev board. The Maple has been EOL’d, and that means it’s time for a few new boards that build on what LeafLabs left behind.

This Hackaday Prize entry is for an almost-clone of the Leaflabs Maple Mini. It sports a newer microcontroller, but still has the same bootloader and pinout. The best part? It costs less than four dollars.

The microcontroller inside this Maple Mini clone is the STM32F103, a 32-bit ARM Cortex-M3 running at 72 MHz with 128K of Flash and 20K of SRAM. That’s enough for just about everything you would want to throw at it. It also follows the pinout of the original Maple Mini, and the team also has a version that’s a slight improvement of the original Maple.

The big deal is, of course, the price of the board. It’s four bucks, or about the same price as an Arduino clone from the usual online retailers. Now, finally, there’s a reason for you to wash your hands of the Arduino too.

Nissan Leaf Batteries Upgrade Old Truck Conversion

[Jay]’s Chevy S-10 electric conversion needed new batteries. The conversion was originally done with a bank of lead acids underneath the truck bed. With lithium battery factories so large they can boost an entire state’s economy being built, [Jay] safely assumed that it just wasn’t worth it to spend the money to replace it with a new set of the same.

Just like unwrapping a present, from around a tree.
One brand new battery pack!

You should remember the beginnings of this story from our coverage nearly a year ago. Being the kind of clever you’d expect from someone who did their own EV conversion, he purchased a totaled (yet nearly new) Nissan Leaf with its batteries intact. It took a little extra work, but after parting out the car and salvaging the battery packs for himself he came out ahead of both a new set of replacement lead acids and an equivalent set of lithium cells.

He has just completed the first test drives with the conversion, having built 48 Leaf cells into blocks resembling the volumes the old batteries occupied. He had to add some additional battery management, but right-off-the-bat, the conversion netted him more amps and 650lbs (295kg) less weight for the same power.  Nice!

We linked to all the posts tagged leaf on [Jay]’s blog. There’s a lot going on, and the articles aren’t all linked to each other. It’s a really cool build and there are definitely tricks to learn throughout the whole process. If you have an hour to kill, [Jay] recorded the entire 26-hour process in a 66-minute video that is embedded below. It’s fun to watch him build up and mount the different modules and gives you a deep appreciation for his devotion to the project.

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[Jay] turns over a new Leaf, scores batteries

[Jay] got a pretty good deal on a low milage Nissan Leaf battery. Unfortunately, it came wrapped in a wrecked Nissan Leaf. There are more and more electric cars on the road each year, and that means there are more cars coming off the road as well due to accidents. Electric cars are specifically designed to protect their batteries, so as we’ve seen before with Tesla vehicles,  a salvage car often will still contain a serviceable battery pack. [Jay] used this knowledge to his advantage, and walks us through his experience buying, testing, and dismantling Hoja, his very own salvage Leaf.

[Jay] set up an account on Copart, an auto salvage auction website here in the USA. “Live” online Auto auctions tend to work a bit differently than E-bay, so [Jay] walks us through the process of buying the car, and gives some tips for getting through the process. [Jay’s] particular car was delivered to him on a trailer. It had been rear ended so hard that the rear tires were not usable. The car was also electrically dead. Thankfully, the electrical problems turned out to be a discharged 12 volt accessory battery. A quick charge of the accessory battery caused the Leaf to spring to life – and display a ton of trouble codes. [Jay] cleared the codes with his trusty OBD II scanner, and the car was ready to drive, at least as much as a wrecked car can drive. It did move under its own power though – with the rear end riding on dollies.

Now that the battery was known to be good, [Jay] set about liberating it from its crushed Leaf cocoon. Nissan’s service manual assumes one would be doing this with a lift. [Jay] had no such luxuries in his driveway, so he used 3 floor jacks to lower the 600 lb battery and dollies to pull it out from under the car.

Click past the break for the rest of the story.

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Benchmarking USB transfer speeds

boards

[Paul Stoffregen], creator of the Teensy series of microcontroller dev boards, noticed a lot of project driving huge LED arrays recently and decided to look into how fast microcontroller dev boards can receive data from a computer. More bits per second means more glowey LEDs, of course, so his benchmarking efforts are sure to be a hit with anyone planning some large-scale microcontroller projects.

The microcontrollers [Paul] tested included the Teensy 2.0, Teensy 3.0, the Leonardo and Due Arduinos, and the Fubarino Mini and Leaflabs Maple. These were tested in Linux ( Ubuntu 12.04 live CD ), OSX Lion, and Windows 7, all running on a 2012 MacBook Pro. When not considering the Teensy 2.0 and 3.0, the results of the tests were what you would expect: faster devices were able to receive more bytes per second.  When the Teensys were thrown into the mix, though, the results changed drastically. The Teensy 2.0, with the same microcontroller as the Arduino Leonardo, was able to outperform every board except for the Teensy 3.0.

[Paul] also took the effort to benchmark the different operating systems he used. Bottom line, if you’re transferring a lot of bytes at once, it really doesn’t matter which OS you’re using. For transferring small amounts of data, you may want to go with OS X. Windows is terrible for transferring single bytes; at one byte per transfer, Windows only manages 4kBps. With the same task, Linux and OS X manage about 53 and 860 (!) kBps, respectively.

So there you go. If you’re building a huge LED array, use a Teensy 3.0 with a MacBook. Of course [Paul] made all the code for his benchmarks open source, so feel free to replicate this experiment.

Python on a microcontroller

The team at LeafLabs was looking for something cool to do with their new ARM development board. [AJ] asked if anyone had ever played around with Python, so [Dave] cooked up an implementation of PyMite and put it on a Maple board. While the writeup is only about blinking a LED with a microcontroller, they’re doing it with Python, interactively, and at runtime.

The build uses the Maple Native board the team is developing. The board has a 32-bit ARM chip with 1 Meg of RAM – more than enough horsepower to run PyMite. The tutorial for putting PyMite on a Maple is up on the LeafLabs wiki.

PyMite is theoretically able to control every pin on the Maple Native and do just about everything a regular Python distro can do. The LeafLabs team is still working on the necessary libraries for their board (although we don’t see anything on the Google code page), so right now only blinking the LED is supported. Still, it’s pretty cool to have Python in your pocket.

What Development Board to Use? (Part Two)

We asked for responses to our last Development Board post, and you all followed through. We got comments, forum posts, and emails filled with your opinions. Like last time, there is no way we could cover every board, so here are a few more that seemed to be popular crowd choices. Feel free to keep sending us your favorite boards, we may end up featuring them at a later date!

Continue reading “What Development Board to Use? (Part Two)”