Compass PCB prototype 02

Building on the Compass PCB prototype 01 I’ve updated the PCB so that I can install the 16 boards easier, along with doing some little things to reduce the amount of wires which will need to run this array.

LED PCB v0.4I created a Ground Bus which I can solder to Board 01 from the Arduino GND and then daisy chain the next 15 together, so I get rid of 15 unnecessary wires. I then moved the +5v feed (which will come from the shift registers) to the top, so I can solder wire, straight, or angled headers depending on what I decide. Lastly, I moved the support holes to the center so that I will be able to flip the board one way or another to install it. This will allow me to manage the 16 wires which go back to the shift registers in a logical way. How I will do that is for another day, at least I know I have options, and I’m giving myself some flexibility here.



Prototype 3 – Shift Registers

Now that both the GPS subsystem is at a good place and there is some material exploration going on, it is time to look at how to turn on a large amount of LED’s.

Photo by SparkFun

Shift Registers are fun little digital circuits where all they do is continually cascade bits, shifting in the data present at input and shifting out the last bit. The nice result is that you can drive multiple items – such as large array of LED’s – with only three pins: a clock pin, a latch pin which stores the data, and a data wire. I don’t know the upper limit, but at some point there becomes too many IC’s to sync at the right speed and you have too many LED’s to run off of the given power.

So now I can drive a n = (∞ − 1) amount of LED’s for the lamp itself, with power being the limiting factor, and have room for other items.  The upshot is that I can now easily drive the Compass subsystem –  an array of 16  LED’s which correspond to the 16 cardinal directions. Combining the GPS output from Prototype 1 with two shift registers was easy – with the help of Serial to Parallel Shifting-Out with a 74HC595 from Arduino. Mostly it is a lot of wiring and making sure that you have the clock, latch, and data wires connected properly. The hardest part was finding enough resisters to connect all the LED’s so they wouldn’t short out.

Here’s a photo of the prototype board, on the roof once again since the GPS module is having a hard time acquiring a signal from the satellites.

Prototype 3