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First serious project. Is Metro the right board?
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Please be positive and constructive with your questions and comments.

First serious project. Is Metro the right board?

by SkyRyder on Fri Sep 10, 2021 3:30 am

Hi all,
I have Trinket M0 experience, and found it to be a fun and capable board, but now I need to launch a project where I will want the best Arduino hardware out there (matched to my needs)

I will be monitoring temperatures
I will be controlling motorized valves (under 500 mA)
I will be controlling water pumps (under 500 mA)
I will be displaying data and status (graphical) and intend to use a capacitive touch screen
I will need to store data
I will want to be able to send email or even text alerts
I will need to be able to sound an audible alarm

For temperature readings, I may be using a variety of thermocouples which need sensitivity in the millivolt range. Perhaps there are boards that do this specialized task?

Anyway, I'm not familiar with the Metro and Metro Express... cost is not important to me, but reliability (including a battery backup and booting into an operating state in case of a power disruption) are going to be important.

If there are different products I should be looking at, please do point me toward them.

Thanks for your kind help.

SkyRyder
 
Posts: 35
Joined: Fri Mar 06, 2020 6:05 pm

Re: First serious project. Is Metro the right board?

by adafruit_support_bill on Fri Sep 10, 2021 6:35 am

When selecting a board, you typically work backwards from the requirements. It sounds like your project will likely need more I/O pins than are available on the Trinket. So you first need to detail those requirements so you can determine the number of pins required and what compatible interface boards are needed.

We have several types of thermocouple amplifier boards with analog, SPI and i2c interfaces. https://www.adafruit.com/?q=thermocouple&sort=BestMatch

Motorized valves will likely require a driver with reversing capabilities (i.e.an H-Bridge) such as our motor shield. These can control 4 DC motors each - and are stackable for more channels. https://www.adafruit.com/product/1438

Water pumps are generally unidirectional and can be controlled with a simple transistor circuit, though the motor shield would work for them as well.

There are many displays to choose from. It would help to sketch out your intended screen layout to estimate the size and resolution required. https://www.adafruit.com/?q=display+tou ... =BestMatch

The Data Logging shield provides SD card read/write capability: https://www.adafruit.com/product/1141

There are many options for Wireless communication, but the M4 Express AirLift has it built right into the board:
https://www.adafruit.com/product/4000

If more pins are required for your application, we also have the Grand Central boards: https://www.adafruit.com/?q=grand+centr&sort=BestMatch
That could be combined with an Air Lift shield for WiFi capability: https://www.adafruit.com/product/4285

adafruit_support_bill
 
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Re: First serious project. Is Metro the right board?

by SkyRyder on Fri Sep 10, 2021 2:18 pm

Thanks for the comprehensive reply! Now, do I understand that Metro Express is designed specifically for Circuit Python?

Is there an advantage to using this board + CP for this kind of project? I'd like to understand this choice before I pull the trigger on the main board.

Let me see if I can improve my question: is it the case that the Express version allows for the easy *addition* of Circuit Python... but I still have the option of the standard arduino + libraries? Might it be the case that some hardware has no python libraries to support it?

Thank you!
Last edited by SkyRyder on Fri Sep 10, 2021 2:47 pm, edited 1 time in total.

SkyRyder
 
Posts: 35
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Re: First serious project. Is Metro the right board?

by SkyRyder on Fri Sep 10, 2021 2:33 pm

OH, I almost forgot.

There may be a good reason to locate some of the temp sensing hardware in a more remote location (with the pump)...

Is I2C such that I can read a couple of thermocouples as well as control the pump (about 15 feet from my main controller hardware.

Thank you.

SkyRyder
 
Posts: 35
Joined: Fri Mar 06, 2020 6:05 pm

Re: First serious project. Is Metro the right board?

by adafruit_support_bill on Fri Sep 10, 2021 2:34 pm

Any of the Metro boards can be programmed via the Arduino IDE. The "Express" boards have sufficient resources and firmware to support programming in CircuitPython also.

Python is an easy language to learn for novice programmers. However it is somewhat resource intensive. Since it is an interpreted language, it requires substantial memory for libraries. And execution speed is not on par with Arduino/C++ code.

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Re: First serious project. Is Metro the right board?

by adafruit_support_bill on Fri Sep 10, 2021 2:39 pm

i2c is a short-range protocol. Going much beyond a couple of feet generally requires some assistance. We have an active pullup module that can overcome the added line capacitance of a longer bus: https://www.adafruit.com/product/4756

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Re: First serious project. Is Metro the right board?

by SkyRyder on Fri Sep 10, 2021 2:50 pm

Wow... such great responses... thank you ever so much. My shopping list is coming together pretty quickly.

For I2C addressing, I plan on one K type module, and one that works with all thermocouples... this ought to make addressing on I2C easier... or is it the case that one module might support multiple sensors?

SkyRyder
 
Posts: 35
Joined: Fri Mar 06, 2020 6:05 pm

Re: First serious project. Is Metro the right board?

by adafruit_support_bill on Fri Sep 10, 2021 3:05 pm

All our thermocouple amplifier boards are single-channel boards.

The MCP9601 supports most common thermocouple types and you can have up to 8 of them on the same i2c bus. https://www.adafruit.com/product/4101
If you need more than that, you can use an i2c multiplexer to create additional i2c buses:
https://www.adafruit.com/product/2717

The MAX31850K '1-Wire' board is for K-type only. But you can have any number of them controlled by a single pin. The down-side is that the 1-wire protocol is pretty slow, so it not the best choice if you need high sample rates. https://www.adafruit.com/product/1727

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Re: First serious project. Is Metro the right board?

by SkyRyder on Fri Sep 10, 2021 3:25 pm

I think I'd like to keep it all I2C...

At the far end of my I2C will be the need to switch on a pump (150mA nominal... more at start)... is there an I2C compatible module that would switch this? I can't really use the shield because that would have to be with the interface hardware...

I see the 3190, but I don't think that's I2C

Thank you again.

SkyRyder
 
Posts: 35
Joined: Fri Mar 06, 2020 6:05 pm

Re: First serious project. Is Metro the right board?

by adafruit_support_bill on Mon Sep 13, 2021 5:40 am

You could use an i2c GPIO expander such as this: https://www.adafruit.com/product/4886
plus a transistor to switch the current.

Or you could use a motor wing: https://www.adafruit.com/product/2927
The Wing is designed to plug into a Feather processor. But you can wire it to your Metro's i2c bus. You just need connections for GND, 3.3v, SDA and SCL.

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Please be positive and constructive with your questions and comments.