Seeking Feedback: Arduino Compatible Shields to Include in Upcoming MicroZed Roadtest

Given that most shields (all ?) from Adafruit and Sparkfun make use of the 5V power output for LDOs . Ex: TFT shield, ESP32 coo-processor  it may be easier to provide a protoshield kit and have the user assemble a humidity / IMU sensor on it directly in order to wire power directly to 3.3V

https://www.sparkfun.com/products/13820

A PMOD can be more useful here.

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Also , the carrier card audio outputs looks like there are not populated.

I'm surprised to see a MicroZed road test as we had one only about 18 months ago. However, back then I found that the lack of connectivity was an issue and limited what I could do to some degree. It's good to see a carrier board will be included. This to me is more important that what shield goes with it.

I suspect most road testers will have a suitable shield to use but Gough Lui raises a good point about patchy compatibility. (Who uses 5V these days though?) I'd suggest that Pmods might be a better fit than Arduino shields as many of these are designed to work with FPGA boards.

Thank You!  I was a bit concerned myself about these boards. I appreciate everyone's time in looking into this for me. You are a valuable resource.

Randall

A watch-out: the gas-humidity-temp shield will not operate ok with the MicroZed.

The PCB layout of the carrier card prevents the free air flow that this shield needs.

I would be particularly concerned about the compatibility of traditional shields with the MicroZed and carrier board. Many of the older shields were designed with the implied understanding that they were to be used with a 5V I/O Arduino - this is especially the case for those prior to the Uno V3 layout which introduced the IOREF pin, but even then, shields that include such a pin may not actually use it.

Specifically, the Sensirion shield you linked has a schematic which implies it is designed for 5V usage - it pulls the I2C lines up to 5V while ignoring IOREF pin entirely:

If the MicroZed and carrier board does not have a level shifting circuit onboard and do have a 5V supply to the shield, then damage to the I/O pins of the FPGA is likely to result (as far as I know, since the Zynq-7000 series seems to only support up to 3.3V I/O as far as I know). Advising the recipient to modify the shields to make them safe for use is one option, but blindly using any shield is not an advisable move.

The Arduino 9-axis Motion Shield you linked uses the IOREF pin, but note that all the accessory ports make the potentially dangerous mistake of just providing 5V to them - so if the user plugs in any additional accessories, they may well end up pulling up the bus to 5V on their own ... rather than IOREF which those accessory connectors don't have access to. Unfortunately, this is just one of those "quirks" of the de-facto shield "standard" which really isn't one at all.

Thus a closer look at the carrier card design is necessary. The carrier card sheet seems to suggest the Arduino connectors are connected directly to the MicroZed with no indication of level shifters -

Looking at a high-resolution image seems to confirm this:

The hardware user guide also confirms this to be the case - no support for 5V shields (!!!)

Luckily, it seems neither shield can cause damage as the carrier board just doesn't provide a 5V line at all. The Sensirion shield may partially work even without a 5V source as long as an external I2C pull-up is used, as the 1V8 rail for the sensors is derived from 3.3V. The RGB LEDs on the shield will not function as they require 5V Vdd line. This also means that the 9-axis board won't be able to power any downstream accessories on its headers either without the 5V line (but avoids potential damage and the onboard IMU should still function to the best of my knowledge based on the schematic).

Perhaps a careful check of the schematics is to be advised for any shield you might consider using with the carrier board to confirm its design is of 3.3V I/O and does not use the 5V line (or can function without it).

- Gough