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How do I connect to a Arduino Nano for serial communication using the GPIO pins? I understand that USB is easier, and already use that for development, but I don't have room in my enclosure for a big USB cable. I have an 74AHCT125N Level Shifter but I don't understand how to wire anything. Everything else I can find online just says "just use USB" or "you need a level shifter".

Chase Cromwell
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    Is you level shifter the base chip or on a carrier board? –  Apr 01 '20 at 00:24
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    @Andyroo it's in a "breadboard compatible" style chip. https://www.adafruit.com/product/1787 – Chase Cromwell Apr 01 '20 at 00:37
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    It looks like I might need a bi-directional logic level converter? And the 74AHCT125N I have isn't bidirectional? Can the same thing be achieved using resistors for serial communication? – Chase Cromwell Apr 01 '20 at 00:53
  • You can use HCT125 one direction, HC125 or CD4050 etc other direction, or bidirection converters: https://raspberrypi.stackexchange.com/questions/27928/power-a-5v-relay-from-gpio-pins. – tlfong01 Apr 01 '20 at 01:27
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    @tlfong01, Am I correct in understanding that because the Arduino is 5v and the Pi is 3.3v logic, the Pi TX to Ard RX connection can just be a straight connection? And the Ard TX to Pi RX connection is what I need to adjust? – Chase Cromwell Apr 01 '20 at 01:50
  • Ah, let me see. Your question asks "GPIO" but not specifically "TxD and Rxd" for UART /serial so my answer is generic, for all GPIOs including relay GPIO. Actually if you are only interested to convert TxD, RxD between 3V3 and 5V0 logic level, then I can give a more detailed answer. Please clarify or confirm that my guess is correct. Comments and counter suggestions welcome. Cheers. – tlfong01 Apr 01 '20 at 03:14

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