Measure voltage of data output?

Question

I'm trying to control a few NeoPixels using a 3.3V Particle Photon.

I've got a 5V power source that I'm using to power the NeoPixels (as they require that voltage. That works fine.

Them I'm using a 74AHCT125 level shifter to increase the data signal from the Photon from 3.3 to 5.

But I'm seeing sporadic response from the NeoPixels and my hunch is there's something wrong with the power output from the 74AHCT125.

Is there a way I can measure the voltage from the data output of the 74AHCT125? I tried connecting the wire from the 74AHCT125 to my multimeter but I'm not getting any measurement from it.

Answer 1

The reason your mulitmeter is not telling you much is probably because it reads some sort of averaged voltage, and your signal is flipping between low and high very rapidly.

If you had an oscilloscope you could easily have a look and see what the peak-to-peak voltage is, but since you don't you'll have to find another way.

If you have some basic electronic components at your disposal, you could knock up a simple peak voltage front-end for your multimeter - this looks like roughly the right thing. You'll need to calibrate it with a known 5v level (i.e. see what reading your meter tells you for a fixed 5v supply) because you'll drop some voltage across the diode.

Otherwise perhaps you could use an analogue input of a 5v Arduino: write a simple sketch to measure (very rapidly!) and tell you the maximum reading every second, say. I don't know off hand how fast the Uno will sample, or the clock rate of your Neopixels - you'll need the Arduino to sample at least as fast as your clock rate.

For the purpose of a quick hassle-free check, I'd probably plump for the first option.