Feb 022014

I’ve decided to use an Eggbot control board, the EiBotBoard, to drive my polar plotter.
Not for any particularly wonderful reason. The board costs right at $50, which is the cost of an Arduino uno R3 ($30) plus an Adafruit Motor Shield ($20).

It seems the software to drive a polar plotter already exists for the Arduino / motor shield combo. Eggbot board, not so much.

So I’m looking at the same cost and more work to use the Eggbot board. But hey, if it was too easy it wouldn’t be fun :). I like the form factor of the EiBotBoard and if I can get it working as a polar plotter I can add a little back to the community.

I ended up buying the EiBotBoard from Sparkfun, the stepper motors from Pololu (on black friday sale for $14 each), the power wart from Adafruit.

The motor mounts, filament spools, and gondola I’ll download from Thingiverse and print them myself.

I’ve decided on the following parts:

Motor Mounts






I’ll probably download and print a few different styles of gondolas and see if I like any of them better than the others.

Progress is being made ….

Dec 312013

The Arduino Pro comes with a bootloader installed, meaning it is plug and play ready to work with the Arduino environment. All you need is a way to hook it up to upload new firmware.

The Pro is a stripped down version of the Arduino UNO. One of the stripped parts is the USB to serial programming interface. Programming the Pro requires either an ISP programmer or a USB to serial translator.

The Pro brings out the standard green to black FTDI cable programming header and Sparkfun recommends their FTDI programming cable (5V) for a plug and play experience. That is all well and good but a FTDI cable is pushing a cost of $20 USD (Sparkfun’s 5V and Adafruits 3.3V). You can buy FTDI breakout boards with the same pinout for a little less, around $15 USD (Sparkfun, Adafruit). That’s better than $20 but still more than twice the cost of other options.

If you are willing to wait for the shipping from China (or you order ahead) you can get a FTDI breakout for less than half the price of the Sparkfun or Adafruit breakouts. The iTeadStudio FOCA breakout has a couple of nice features over the Sparkfun and Adafruit breakouts, and one glaring hassle. First the good, the FOCA interfaces with either 5V or 3.3V systems with the flick of a switch. The FOCA also has an XBEE footprint allowing it to be used as a USB to XBEE interface (compare to Sparkfun’s USB to XBEE board at $25). All in all a pretty nice package for $6.50 USD (as of Dec 2013).

iTeadStudio FOCA

iTeadStudio FOCA

Now for the hassle part. The pinout of the FOCA is NOT a direct crossover to the “standard” green to black programming pinout on Sparfun’s and Adafruit’s FTDI cables, and of course the pinout on the Arduino Pro.

The pinout on the Pro is green to black being reset/dtr, TX, RX, power, cts, gnd.

Sparkfun Arduino Pro

Sparkfun Arduino Pro

The pinout on the FOCA is power, TX, RX, gnd, dtr/reset. Not a straight across plug and play.

FOCA Pinout

FOCA Pinout

Fortunately for half the price it is pretty easy to make an adapter cable. I happened to have a 6 pin to 6 pin inline cable with crimped on connectors which made it easy to move the pins around.

The pins are held in place by little plastic fingers that can be easily lifted back with the tip of an Xacto knife or dental pick, allowing each pin to be slid out of the connector and moved to a different position.


A quick shuffling of both ends of the connector, to move green to one end and black to the other end on the Pro side, and to line up power, gnd, TX, RX, and reset on the FOCA side and wa-la, a FTDI programmer for under $7.50.