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

I wasn't able to find any official voltage parameters for the HM-19 module, but these product specifications indicate that the maximum input voltage to the HM-19 modules is 3.7V. Could the issue be that you're supplying the module with too high of a voltage, and that is what's causing issues? Also, is the nRF52840 set to VDDH mode, so that it supports 5V as well?

You can use a logic analyzer to check what happens on the TX and RX lines to see if there is any activity at all.

Best regards,

Simon

[ephimee]

I'm using the DSD TECH HM-19, which is rated 3.6 .. 6v.

I think it has a built in LLC.

I'm not familiar with VDDH? 5V is written on the P13 header on the NRF PCB so I assumed that the I/O is also 5V?