search

EnviroDIY / EnviroDIY_Mayfly_Logger

hardware design files, example code sketches, and documentation for Arduino-framework EnviroDIY Mayfly data logger
https://envirodiy.org/mayfly/
Other
31 stars 26 forks source link

UART RXD0 Pullup Qu #28

Open neilh10 opened 3 years ago

neilh10 commented 3 years ago

On the Mayfly 0.5b the UART RXD0, Processor Pin9, is a CMOS input. Under normal operation mode when it is deployed it would be in UART mode and it would appear to float. I'm curious, its normally good practice to pull up/down high impedance CMOS inputs, so that they can't oscillate. Was this considered for this input. When a user is using the FTDI and is powered VUSB/5V_FT, it would be driven, but this is typically only when its in development mode with USB cable plugged in. I seem to have seen an occasional stream of unexpected UART RX ~ however its difficult to characterize, I have had unexpectedly variable power measurements which could explain variability I've seen in #21

neilh10 commented 3 years ago

With a special test build that counted polled "debug" UART input I verified that there is autonomous characters received. Running for ~ 48hours, with the UART RX not connected to anything, it counted "6528 characters" received.

neilh10 commented 3 years ago

I've created a dongle that can be plugged into J2 "FTDI Programmer" that pulls pin3 down with a 1M R. It pulls it down as that is the null condition, and if U4 FT232RL is not powered, don't want to pull up its corresponding port.