Does Navigator board use SPI?

[coanderson]

Hi there, I’m guessing that the navigator board is using all of the RPI pins, but I wasn’t sure about SPI pins because the navigator only has UART/I2C connectors exposed.

I would like to know because I want to use this hat (not as a hat, but I’d use it as a breakout) with the PI that the navigator sits on top of to allow us to record hydrophone data. The github page for the DAQ Hat library explicitly says this about the board:

The MCC DAQ HATs are compatible with all Raspberry Pi models with the 40-pin GPIO header (not the original Pi 1 A or B with the 26-pin header.) They are generally not compatible with any other brand of Raspberry Pi HAT or add-on board that attaches to the GPIO header, or devices that use the Raspberry Pi SPI interface.

In particular, LCD displays that use the GPIO header (not HDMI) usually use the SPI interface and will prevent the DAQ HATs from working. Even if the display is removed, the driver is probably still loaded by /boot/config.txt and will cause issues with the DAQ HATs. If you have a problem with your device and have used a GPIO header display with your Raspberry Pi then consult your display hardware documentation for how to remove the driver.

I’m sure this means that I cannot use the same PI for this hat and the navigator, but I wanted to check just in case I am wrong–I would love for them to be compatible.

Thanks!

[tony-white]

Hi @coanderson -

You’re correct, the Navigator uses SPI to communicate with the magnetometer, as detailed in the schematic on the product page, also linked here. Beyond that, stacking a hat like that with a Navigator would be challenging from a hardware perspective - both fitting in an ROV 4" housing and generally modifying the GPIO headers to accommodate a stack…

What are you trying to measure? The Navigator already has 2x analog to digital converters, although they may not be as performant as the hardware you’ linked… are you trying to output an analog voltage for some purpose? I’m curious about your application’s goals!

[coanderson]

We need more bits and a higher sample rate than the ADCs on the navigator unfortunately. The diagram below is a rough idea of what I’m trying to make. This will not be in a BlueROV, it will be in a standalone pressure case that we will be towed with some other instruments. The navigator is overkill, but we already have one and y’all make it easy to integrate the sensors we want!

[tony-white]

Hi @coanderson -

Gotcha!

I’ve tested an ethernet based hydrophone, and also used other hydrophones with USB sound-cards in the past - maybe this would eliminate the need for a second Pi?