Step 35: Build the controller: Power rails and IC power
Large circuit boards like this one, with lots of wires, can become quite confusing. We always try to avoid lifting the GND and VCC lines off the board. We solder them as continuous solder lines. This makes it very easy to identify what is GND/VCC and what is signal lines.
If the VCC and GND lines needs to cross paths, simply route one of them over the other using a piece of wire on the top side of the PCB.
In the first picture you can see some solder traces in place.
The two horizontal traces is the "main power bus". The lowest one is VCC and the top one is GND. For every row of ICs a GND and VCC line is forked off the main power bus. The GND line runs under the ICs, and the VCC line runs under the resistors.
We went a little overboard when making straight wire for the cube, and had some pieces left over. We used that for the VCC line that runs under the resistors.
In the bottom right corner, you can see that we have started soldering the 8+1bit bus connecting all the latch ICs. Look how easy it is to see what is signal wires and what is power distribution!
In the second picture, you can see the board right-side-up, with some additional components soldered in, just ignore them for the moment.
For every latch IC (74HC574), there is a 100nF (0.1uF) ceramic capacitor. These are noise reduction capacitors. When the current on the output pins are switched on and off, this can cause the voltage to drop enough to mess with the internal workings of the ICs, for a split second. This is unlikely, but it's better to be safe than sorry. Debugging a circuit with noise issues can be very frustrating. Besides, capacitors make the circuit look that much cooler and professional! The 100nF capacitors make sure that there is some current available right next to the IC in case there is a sudden drop in voltage. We read somewhere that it is common engineering practice to place a 100nF capacitor next to every IC, "Use them like candy". We tend to follow that principle.
Below each row of resistors, you can see a tiny piece of wire. This is the VCC line making a little jump to the top side of the board to cross the main GND line.
We also added a capacitor on the far end of the main power bus, for good measure.