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

 

Randy