lo noise stuff

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BJB

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Am doing some lo-noise stuff (per CISPR22/32 class B limits). For various reasons, not all related to noise, cannot exceed a 24MHz clock.

Have tested various ATtiny and other AVRs, and some M0 and M4 STMs, and some TI 430s, and Teensy models 3.2, 3.5, and LC. So far, the two most 'quiet' processor modules have been an ardy pro mini (a China clone) and the Teensy LC. For obvious reasons, will not put the former in a fielded product, so am planning to use the latter T-LC, but with an external ADC.

Without resorting to shielded enclosures, etc, any low-noise microcontroller recommendations? Is there something special about the PCB layout for the T-LC that was done to reduce emissions?
 
You've set Tools > CPU Speed to 24 MHz, right?

Have done things much more stupid than this, so verified the ardy IDE config for 24MHz on the tech's windoze box and is correct. Mine typically uses SCons on Linux, so very little mouse clicking or thinking is required on my part, so is difficult for me to screw this stuff up (famous last words). Would have gone to lower clock, but needed USB.

The T-LC is over-kill for this, but no care, as will only make of few of these widgets and want it to be reliable. So for now, am just curious why the T-LC is a quiet and respectful neighbor, while the other boards are making noise.
 
So for now, am just curious why the T-LC is a quiet and respectful neighbor, while the other boards are making noise.

Difficult to say. Teensy LC doesn't have anything particularly special for RF low noise, only good quality components, but a pretty generic 2 layer PCB design. Freescale did a good job in the design of the chip and Teensyduino uses the slew rate limiting feature of the pin by default, so if your code is toggling the pins frequently, that slew rate feature might be helping quite a bit.
 
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