I need to communicate with some Dynamixel servos from a Raspberry Pi. There’s a commonly published circuit to achieve this using a 74LS241 buffer to

Is it valid to connect a 5V 74LS241 output to a 3.3V Raspberry Pi input?

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2021-05-12 02:21:04

I need to communicate with some Dynamixel servos from a Raspberry Pi. There’s a commonly published circuit to achieve this using a 74LS241 buffer to manage the half duplex connection. (This page lists several versions, all essentially the same: https://pypi.org/project/pyax12/).

However, it connects a 5V part directly to the Pi inputs, which as I understand it aren’t 5V tolerant. Is this circuit valid? It seems to be widespread, so why isn’t it breaking things?microcontrollerdigital-logicShareCiteEditFollowFlagasked 19 hours agoAncient James3333 bronze badges New contributor

This circuit was most likely designed by a non-EE. LS TTL parts have weak high-side drivers so it may marginally work, but NOT recommended. A 74AC241 has strong high-side drivers and would probably damage the RPi.

simulate this circuit – Schematic created using CircuitLabShareCiteEditFollowFlaganswered 17 hours agoMattman9448,45311 gold badge1111 silver badges3131 bronze badges