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

If the HM-19 is set to 3.6V it should be sufficient to set the DK in normal operating mode, powering it from J2 and having the power select switch set to VDD. Please check if you have any luck here, or else I'm not quite sure on what to look at next. I still suggest trying with a logic analyzer to see what's going on on the TX/RX lines themselves. Are there any differences in how the FTDI and HM-19 transmit and receive?

Best regards,

Simon

[ephimee]

I don't have a logic analyzer.

On the DSD TECH HM-19 it's written 3.6 .. 6V which means it should work with 3.6V but also 5V.

I also just tried to connect the DSD TECH HM-19 to a Arduino Uno, and that is also working fine.
The Arduino Uno is 5V logic.

I also have a Wemos D1 Mini with a ESP8266, which is running on 3.3v.
I tried connecting this as well and it's working fine with the DSD TECH HM-19.

Then I also tried connecting the FTDI to the DSD TECH HM-19, but this time I set the jumper to 3.3v. And also that is working fine.

So I think maybe the problem is in the software settings on the NRF?
I'm pretty new to Nordic, so I could've easily overlooked things?