UART logic level

[theseankelly]

Hey -- I'm curious whether the UART1 & UART2 pins on the headers are 5v tolerant for interfacing with 5v UART peripherals.

I read that the UART on the bigquad deck is 5v tolerant -- does it drive 5v signals?

I'm hoping to interface with both a 5v GPS and a 5v OSD for my bigquad build, and am trying to determine if I need to plan on some level shifting.

Thanks
Sean

[tobias]

Hi Sean,

Yes the UARTs are 5V tolerant however they output 3V. It shouldn't be a problem communicating with a 5V device but it might be wise to check how they interpret high and low signals to be sure.

[theseankelly]

Gotcha. What about on the BigQuad deck (the GPS pins)? The presence of the 5v supply pin implies the Uart is stepped up to 5v there.

Also, what's the range for Voh on the Crazyflie's 3v output?

Sean

[tobias]

The BigQuad deck is intended to be powered through a 5V supply, this will also power the CF2. All 5V supply is connected together so either a ESC with a 5V BEC output can power it or a dedicated 5V DC/DC or similar. Please see schematics for details.

That means that the UART voltage levels might not match but if they don't differ to much it shouldn't be a problem. I'm not sure what the "standard" GPS modules output voltage is but they might be 3.3v or 5v and both should work.

[theseankelly]

Right -- I just mean that since there's a 5v supply pin on the "GPS" bank, that implies the GPS uart is being stepped up to 5v on Tx, but it sounds like it's actually still driving at 3.3v?

[theseankelly]

Uh oh, and a second look at that schematic reveals UART2 is being repurposed for the PPM signal to the ESCs? I guess I'll have to repurpose some other pins if I want to run two UART devices.

[tobias]

Uh oh, and a second look at that schematic reveals UART2 is being repurposed for the PPM signal to the ESCs? I guess I'll have to repurpose some other pins if I want to run two UART devices.

Yes the puzzle begins . Which the STM32 devices had a connection matrix that e.g. the nRF51 has where you can more or less assign a peripheral to any pin (not analog though).