Build the Circuit

In order to run the 5V NeoPixels from the 3V Arduino M0 Pro, we'll use level shifters. You can find out more about this topic in this guide.

For this application, we'll use two of the excellent 74AHCT125 quad channel level shifters.

Each level shifter has a reference voltage pin soldered to the 5V power rail, and a common ground pin. Then, there are four sets of three pins, each constituting a channel for taking in the 3V data signal from Arduino, and outputing it at 5V to the NeoPixel digit, as well as an output enable (OE) pin tied to ground.

You'll bring all of your Arduino pins onto the circuit with a 5-conductor JST SM cable, and go out to the digits, via 1K resistors to five individual 3-conductor JST SM cables. 

A large capacitor (anywhere from 1,000 to 4,700 uF) will sit across the ground and 5V rails to smooth out any voltage spikes.

Run a 9" length of black wire from the ground rail on the proto board -- this will go to ground on the Arduino later.

For any unused channels on the quad level shifter you should tie the output enable pins to voltage (HIGH) with a roughly 1K resistor. Be sure to run voltage from top to bottom rails on the PermaProto board for this to work.

Solder each of the five 3-conductor JST SM cables to the output side of the level shifters paying attention to use the same ground wire, data wire, and power wire configuration as you have on your NeoPixel digits.

Solder a short length of red 26AWG stranded wire to the power rail and a black one to the ground rail, and then screw these into the female DC power jack. This is where you'll plug in the 5V 10A power supply to give juice to the NeoPixels.

Assemble the Proto ScrewShield as per these instructions. Then, wire the end of the 5-conductor JST SM cable to the corresponding pins D4-D8 on the ScrewShield.

Double check that this is aligned with the proper input pins on your level shifter circuit at the other end of the JST connector cable.

Use a single wire to run the PermaProto board's ground rail to a GND on the ScrewShield.

Connect the 5-conductor JST SM connectors to join the Arduino/ScrewShield combo to the level shifter board.

Next, we'll upload a sketch to the Arduino to test out the display!

This guide was first published on Mar 15, 2017. It was last updated on Mar 15, 2017. This page (Build the Circuit) was last updated on Nov 20, 2019.