My previous post has a description and laundry list of parts I used.  I wanted to learn how to use the 74HCT595 shift register chips.  These chips are really cool because you can daisy chain them together and then simply shift bits of data into the DS serial input.  The data will write out across all the chips in the chain and you only need three digital IO ports for any number of 595’s in the chain.  You just write out 8 bits of data for each chip.  So if there are 4 595’s chained together you write out 32 bits of data. 

The 595’s operate 8 active low output ports which means they are LOW when there is a (0) bit shifted in to the corresponding pin’s register and HIGH (Vcc) when there is a (1).  So 2 chips let me turn on the positive columns of the cube.

The MC74HC138A I used let me turn on and off the connectivity to the negative voltage.  I only needed 4 of the 8 pins because I only have 4 horizontal rows of cathodes to switch.

The code attached to this only runs a test pattern that appears to turn on all the LED’s in a layer and cycles to the next layer.  I did this to catch some solder points that came undone.  Next I am going to work on building some animations for the cube like rain, sinking letters, bouncing ball…etc.

Here is my parts list with prices:

2 X 74HC595 Shift Registers @ $0.20 each
64 X Blue 5mm LED’s @ $0.038 each
16 X 470 Ohm resisters @ $0.01 each
1 X MC74HC138A @ $0.29

So that was $0.88 in parts if you don’t count the $29 Arduino.

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