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Using Arduino as a rapid prototyping system

Posted: 08 Sep 2015     Print Version  Bookmark and Share

Keywords:Arduino  prototyping system  LiPoly  NeoPixel  ChipKIT 

I have become a bit obsessed with the Arduino as a rapid prototyping system. Prototyping is a natural subject for me, as I spend my days in the rapid prototyping assembly house, Screaming Circuits, but my obsession with the Arduino for prototyping goes way beyond the manufacturing angle.

At ESC Silicon Valley, I talked about, and wore, an Arduino-compatible electronic show badge (figure 1) that I had thrown together, largely using sections of a couple of older designs. It used the core of an Arduino Leonardo, a LiPoly charging circuit from one of my robot boards, an accelerometer from my electronic business card holder, a real-time clock from my NeoPixel clock, and a TFT display that I'd never used before.

Figure 1: An Arduino-compatible electronic show badge.

It was a last minute idea, and I spent about an hour putting the schematic sections together, and another hour and a half on the layout. It's not my best work—a total hack job, in fact—but ended up working, with just one mod wire and one other small issue.

One of the challenges with the Arduino is that the base units are built around 8bit microcontrollers. They are pretty handy and a lot more useful than a lot of people give them credit for, but it is easy to run out of memory or processing capability. Thus, for my next Arduino-compatible project, I looked to the ChipKIT Arduino from Digilent and Microchip. The ChipKIT uc32 Arduino-compatible is based on an 80MHz, 32bit MIPs architecture MCU from Microchip, with 512K FLASH and 32K SRAM. That's a big step up from the 8bit, 16MHz, 32K FLASH, 2.5K SRAM microcontroller in the Arduino Leonardo.

The PIC32MX340F512H in the ChipKIT has ample capability over and above the standard Arduino. It also runs at 3.3V, which would have helped with the "other small issue" I had with the badge: The accelerometer I used was a 3.3V part, and the battery charger/management chip can output up to 4.5V. Pop went the accelerometer.

The new board took a little longer than the 2.5 hours that I spent on the first badge. I don't have a lot of 32bit design experience, so I spent more time reading datasheets and self-educating myself on the ChipKIT design. In total, it was about two weekends worth of design, layout, and parts finding time, with one of those days being used mostly for design review.

For the most part, the problems I found in my design review matched pretty closely to the manufacturability issues that pop up most often back at the shop with customer boards. I had a number of parts with the wrong footprint, and a few with the right footprint on the board but the wrong part package variant in the bill-of-materials (BOM). I also found an unconnected pull-up resistor on one of the switches. Ironically, that's the same problem that led to the mod wire on my original electronic badge.

One of the downsides of basing a design on open source is that you don't have the tribal knowledge that went into the design decisions. There are a few places where the design deviates from the chip datasheet recommendations. That's not uncommon, but without the water-cooler discussions and o-scope time that went into the original board, I don't know why those changes were made. I'd rather understand what I'm building than just run on blind faith.

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