I want two RPi Picos to talk to each | adafruit | Page 1

karmic creek Sep 1, 2024, 11:02 PM

#

I have some RS-485 breakouts from SparkFun that use the SP3485 transceiver, not sure if that would be an avenue, or if I should do direct UART connections between the two Picos? I have not been able to locate any tutorials or code examples for CircuitPython for this.

#

Can it be done with busio.UART or is that just a software way of having two picos communicate?

#

I currently do not have a lot of money to spend on this project, so I am hoping I don't have to buy more feathers or wings or whatever to make this happen...

#

Goal is essentially: Pico 1 has 6 analog buttons. Whenever these buttons are on/off, it will send a signal to the secondary Pico that sits on a Waveshare Pico-Relay-B board, and it will in turn pull the specified relay low/high.

#

Any help appreciated!

#

Maybe I can use something like this? https://www.adafruit.com/product/5728

Adafruit PiCowbell CAN Bus for Pico - MCP2515 CAN Controller

Ding dong! Hear that? It's the PiCowbell ringing, letting you know that the new Adafruit PiCowbell CAN Bus is in stock and ready to assist your Raspberry Pi Pico and Pico ...

#

Oh, snap, this might be the way to go... but, expensive... https://www.adafruit.com/product/5724

Adafruit RP2040 CAN Bus Feather with MCP2515 CAN Controller

If you'd like quickly get started with CAN bus interfacing, with no soldering required, our Adafruit RP2040 CAN Bus Feather comes ready-to-rock with a microcontroller, CAN ...

#

Or, maybe use some of the QT Py boards I have?! https://www.adafruit.com/product/5877

Adafruit CAN Bus BFF Add-On for QT Py

Our QT Py boards are a great way to make very small microcontroller projects that pack a ton of power - and now we have a way for you to turn many QT Py boards into powerful CAN bus ...

#

Except, then I would have very limited GPIO, right?

#

Anyway. Hoping someone can provide some advice here. Thank you for your time.

lethal hollow Sep 2, 2024, 12:38 AM

#

Can you say more about the data volumes and needed speeds, and the electrical environment (clean or noisy)?

#

CAN should work (#general-chat message) but it the messages are tiny, UART not sure... depends? There is differential for I2C (#help-with-projects message), but that's going to require some specialized programming probably.

#

UART is easy to test with different speeds and parameters, maybe different wiring.

karmic creek Sep 2, 2024, 12:55 AM

#

Data volumes will be relatively low, I am mainly trying to control either relays or MOSFETs to switch higher current loads that are part of a vehicle 12V system.

#

The electrical environment will be relatively noisy, I assume, as part of the network will be present in the engine bay.

lethal hollow Sep 2, 2024, 2:51 AM

#

There is some support for RS-485 in busio.UART https://docs.circuitpython.org/en/latest/shared-bindings/busio/index.html#busio.UART. I'd suggest running some tests with what you have first to see if you can get something reliable enough. There's not a lot of data, and you can probably get by with low speed, so distance and noise are really the critical things. Differential signaling would help.

lethal hollow Sep 2, 2024, 6:06 AM

#

Just tested board.UART() (default 9600 baud) over approximately 40-50 feet of Cat5 cable (just b/c it was handy). Not a noisy environment, but this seems to work fine (short packets with CRC sent and checked). These alternatives are close to the ballpark, but again differential signaling (or at the very least, shielded cable) would really help in your environment. CAN is designed for this kind of thing.

karmic creek Sep 2, 2024, 3:48 PM

#

Thank you, @lethal hollow! I think I'll get some CAN breakouts from Adafruit, then. Can I use regular cable/wire with CAN, or will it require shielded cable?

lethal hollow Sep 2, 2024, 4:06 PM

#

For your distance of 10m in a noisy environment, I'm not sure. There is specifically-designed CAN bus cabling, but if you have some, I'd try regular Cat5-Cat6 Ethernet unshielded twisted pair first. L and H should be on the same twisted pair, and ground need to run through the cable too.

karmic creek Sep 2, 2024, 4:08 PM

#

I think I have a length of industrial cat5 somewhere! I'll see if I can find it.

lethal hollow Sep 2, 2024, 4:12 PM

#

some ethernet cables are shielded, you may get lucky

#I want two RPi Picos to talk to each