Nrf52840 UART device compatibility

[ephimee]

I have 3 devices that can communicate via UART:
1) nRF52840-DK (PCA10056)
2) FTDI (set to 5v logic)
3) BLE HM-19

I'm using the example in ./nRF5_SDK_16/nRF5SDK160098a08e2/examples/peripheral/serial_uartes

If I connect the FTDI to the NRF, I'm able to send and receive data.
ftdi.5v to nrf.5v
ftdi.gnd to nrf.gnd
ftdi.rx to P0.27
ftdi.tx to P0.26

If I connect the FTDI to the HM-19, I'm able to send and receive data.
ftdi.5v to hm.5v
ftdi.gnd to hm.gnd
ftdi.rx to hm.tx
ftdi.tx to hm.rx

But if I connect the NRF to the HM-19, it doesn't work.
hm.5v to nrf.5v
hm.gnd to nrf.gnd
hm.rx to P0.27
hm.tx to P0.26

I have set the baudrate to 9600 on every device.

I tried swapping RX, TX.
I also tried first connecting RX,TX followed by power. Also the other way around power first and then connect RX, TX.

This is how I configure the uart:

NRF_SERIAL_DRV_UART_CONFIG_DEF(m_uarte0_drv_config,
                      ARDUINO_SDA_PIN, ARDUINO_SCL_PIN,
                      RTS_PIN_NUMBER, CTS_PIN_NUMBER,
                      NRF_UART_HWFC_DISABLED, NRF_UART_PARITY_EXCLUDED,
                      NRF_UART_BAUDRATE_9600,
                      UART_DEFAULT_CONFIG_IRQ_PRIORITY);

[Simonr]

Hi Philip

Sorry, I didn't realize you were using the DK. You're powering the board using the 5V pin and not the USB connector, right? Now, this pin does allow an input of 5V, but it will not power the nRF with 5V, but rather 3.3V (VDD mode). This might cause some conflicts when communicating with boards that run on higher voltages, so I suggest you power the board in VDDH mode instead to see if that solves the issue. You can power the DK in VDDH mode by either using the USB connector (J3) and setting the power source switch to USB source, or by through the Li-Po battery connectors (J6 or P27) and setting the power source switch to Li-Po.

Alternatively, you can try powering the HM-19 board with 3.6V instead to avoid voltage level conflicts between it and the nRF52840 in VDD mode. Did you have any luck using a logic analyzer to see exactly what happens on the TX/RX lines?

Best regards,

Simon

[ephimee]

No, I was using J2 USB originally.

I just tried using the J3 and set the switch to USB power source. So basically I'm now using both J2 and J3 USB ports.
The result is the same. FTDI works fine with the DK, but the DK is unable to communicate with the DSD TECH HM-19.

I haven't tried LLC yet. Which pin on the DK is 3.6V I can use?