Teensy input/output voltage compatibility w/ encoder and driver
I'm an ME student working on developing a 6 axis arm as my senior design project, and the AR4 has been an amazing source of inspiration. My team wants to use similar steppers and drivers as well as the teensy 4.1, however we noticed what seems to be an issue when looking at specs.
The encoder that comes with the steppers used in the AR4 says it outputs 5V high on the stepperonline product page, which to my understanding could damage the teensy since it's designed for 3.3V input. Also, the stepper driver user manual says it accepts 4-5V high input, whereas the teensy again uses 3.3V. The AR4 instructions and wiring schematic seem to show that these inputs and outputs are directly connected.
To the best of my knowledge this system shouldn't work, but clearly the AR4 does work using these parts. I was wondering if I'm missing something in the AR4 wiring/the hardware specs/my general electrical understanding, or if the parts can just handle a greater voltage range than what they're rated for, or if there's something else entirely going on?
Many thanks
Jacob
Hi Jacob,
The Teensy 4.1 is a 3.3V device and is not officially rated as 5V tolerant, so I understand the concern.
On the encoder side, although the encoder is powered from 5V, the A/B outputs are driven through the encoder's internal output circuitry, which has finite impedance and limited drive current. The signal is also a pulse train with a changing duty cycle rather than a solid 5V supply continuously connected to the Teensy input. The Teensy inputs also contain ESD/protection structures that help limit small transient currents.
On the driver side, the STEP/DIR inputs have reliably recognized the Teensy's 3.3V output despite the driver's published 4–5V specification.
This configuration has now been used on hundreds of AR robots over several years, and I have not seen any Teensy failures attributable to the encoder signals or reliability issues with the drivers recognizing the 3.3V STEP/DIR signals.
Thank you,
Chris
Chris Annin That makes sense, thank you so much for the response!