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Tuesday, 20 May 2014

The lobstar - An OSH, low-cost, breadboard-friendly Arduino-compatible clone

There's a revolution underway in Computer Science education. The Raspberry Pi has generated a huge amount of energy and enthusiasm, but there's also a lot of interesting activity around the Arduino.

One great Arduino resource is the Shrimp, a low-cost compatible design aimed at educators and hobbyists with limited budgets.

Landing the Shrimp

You can find out more on the Shrimping It blog. It describes
'the Shrimp – a substitute for the Arduino Uno, which can be constructed for about a tenth of the price of the official board, shown here in stripboard and breadboard versions.'
Note the absence of a PCB version! That's deliberate: the idea is that you will lean more, and feel more of a sense of ownership, if you have constructed the shrimp from scratch.

That makes sense but I can see two situations where shrimp-catchers might prefer a PCB to work with.

  1. Some beginners starting out on their own might feel more confident building a PCB; an early win is important for building confidence.
  2. Old hands often want to put something Arduino-compatible at the heart of a prototype, and want a small and inexpensive system-on-a-board, ideally in a DIP format.

Enter the lobstar

The lobstar borrows unashamedly from the Shrimp's minimalist design; it has everything I want for prototyping, but no more. It has a header for In-system programming and a resonator to make the clock accurate enough for Serial comms, I2C and SPI. It plugs into a breadboard, and it has a reset button. And thanks to AVRISP, it has a bootloader.

No LEDs, no power regulator, no USB interface. I don't need them for what I want to do.

Fritzing it

The shrimp has a breadboard version so it was easy to capture and modify the design in Fritzing. I decided to use it as a pilot project while learning how to use Fritzing to generate a PCB design.

Of course, as always happens, I made a couple of mistakes.

Version 0.1 swapped ground and the 5v power on the FTDI header. Amazingly, nothing was damaged, and I was able to program it using a kludgy but effective stripboard.
lobstar v 0.2
Version 0.2 (the one I got made by ragworm) was a significant redesign and I managed to introduce an extra trace which I had to cut through with a craft knife.

Version 0.2.1 is currently on its way back from oshpark. (I used the lobstar as a way of trying out several different PCB fab shops, and will post about my experiences when the next lot of boards arrive.) There's a picture of version 0.2 in yesterday's post.

Even though v 0.2.1 is still untested I have open-sourced the design. You can follow its evolution on Github. oshpark generated a preview to show what the board will look like, shown below.
oshpark preview
The earlier versions are working well (after suitable surgery) and do just what I hoped.

Conclusion


If you want to learn or teach about Arduino on a budget, a shrimping workshop sounds like a great idea. If  you want a source of easy-to-make, easy-to-use, inexpensive Arduino-compatible clones, you can use Fritzing to create your own custom PCB. You could even make use of the lobstar design!