LED Cube 8x8x8

Step 37 Build the controller: Address selector

The 74HC138 is responsible for toggling the clock pin on the 74HC574 latch ICs. We call this an address selector because it selects which one of the 8 bytes in the latch array we want to write data to. The three blue wires running from the connector to the 74HC138 is the 3 bit binary input used to select which of the 8 outputs is pulled low. From each of the outputs on the 74HC138, there is a wire (white) running to the clock pin on the corresponding 74HC574 latch IC.

Start by soldering the GND and VCC connections. If you use the solder trace method to run GND/VCC lines you want to do this before you solder any other wires in place. A 100nF ceramic filtering capacitor is placed close to the VCC and GND pins of the 74HC138.

Then connect the address lines and the 8 clock lines.

If you look carefully at the connector, you can see two pins that are not used. These will be used for a button and debug LED later.

Comments

[paler31]

Hi, just wondered what connections the control pins of the 138 chip should be. I am not quite sure from the pics what the contol pins e1,e2 and e3 are connected to or does it not matter as i dont see it mentiond in the instructions. I think it looks like pin e1 and e2 are connected to ground and e3 to Vcc. is this correct.

[Stevooo1985]

you can find the datasheets online of the chip, there you can see where the pins should go.