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?

[Simonr]

Hi Philip

Would you mind sharing the schematics of your nRF PCB so I could take a look at your setup? I can set the case to private mode if you don't want to share the schematics with the community. In private mode, your case will be treated confidentially, and only yourself and Nordic engineers will be able to see it.

You can read up on normal (VDD) and high (VDDH) voltage mode in the product specification. Specifically section 5.3.

Best regards,

Simon

[ephimee]

I'm using the nRF52840-DK with the PCA10056, so I was referring to this PCB.

There's nothing else to share, I already provided all the details above.

There's a switch on the board to swap between Li-Po, VDD and USB. But only VDD is working.

[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