Notes on nrf52840 breakout
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rbaron
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3 changed files with 65 additions and 12 deletions
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@ -12,7 +12,7 @@ A low power soil moisture sensor based on the nRF52840.
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* Implement ADC for battery monitoring
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* Figure out a way for people to configure the device with a custom name. Idea: BLE service (this is what my [hacked xiaomi temp sensor](https://github.com/atc1441/ATC_MiThermometer) does)
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* Figure out how OTA works (if at all) over BLE
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* Design new board using the nrf52 instead of esp32
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* Design new board using the nrf52840 (E73-C) instead of esp32
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# Done
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* Implement battery level monitoring
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@ -9,14 +9,24 @@
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; https://docs.platformio.org/page/projectconf.html
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[env:e73-tbb]
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platform = nordicnrf52
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board = adafruit_feather_nrf52832
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framework = arduino
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upload_port = /dev/cu.usbserial-14330
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monitor_port = /dev/cu.usbserial-14330
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; build_flags = -DNRF52 -DS132 -DNRF51_S132 -DNRF5
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; [env:e73-tbb]
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; platform = nordicnrf52
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; board = adafruit_feather_nrf52832
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; framework = arduino
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; upload_port = /dev/cu.usbserial-14330
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; monitor_port = /dev/cu.usbserial-14330
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; ; build_flags = -DNRF52 -DS132 -DNRF51_S132 -DNRF5
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; Let's keep it simple for now and just use adafruit_feather_nrf52832.
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; board = e73-tbb
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; board_build.ldscript = ./ldscripts/nrf52832_s132_v6.ld
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; ; Let's keep it simple for now and just use adafruit_feather_nrf52832.
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; ; board = e73-tbb
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; ; board_build.ldscript = ./ldscripts/nrf52832_s132_v6.ld
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[env:nrf52840]
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platform = nordicnrf52
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board = adafruit_feather_nrf52840
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framework = arduino
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upload_port = /dev/cu.usbmodem14101
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monitor_port = /dev/cu.usbmodem14101
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; build_flags = -DUSE_LFSYNT
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debug_tool = jlink
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; build_flags = -DUSE_TINYUSB -DNRF52 -DS140 -DNRF5
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45
resources.md
45
resources.md
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@ -284,4 +284,47 @@ This is a FreeRTOS scheduled task. It seems to work, but by default it wasn't. I
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# Nordic specifics
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* HAL vs. Drivers
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* [Great answer on nordic forum](https://devzone.nordicsemi.com/f/nordic-q-a/5964/nrf_dvr_xxx-vs-nrf_xxx)
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* HAL are lower-level. They provide some functions for accessing registers. Drivers are higher level, and usually use the HAL functions. Drivers can be used with or without SoftDevices.
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* HAL are lower-level. They provide some functions for accessing registers. Drivers are higher level, and usually use the HAL functions. Drivers can be used with or without SoftDevices.
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# nRF52840
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I've started using a standalone nrf52840 module (e73-2g4m08s1c), since I want a barebones module to test power consumption. This chip is very similar to the nrf52832, except it has built-in usb support!
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## Adafruit bootloader
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The bootloader is different. It has one extra feature: double resetting puts the chip into DFU/CDC mode. I actually verified that it shows up as a mass storage device on my mac!
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## Questions
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* Booting in DFU/CDC creates a new serial device in /dev/cu.usbmodem*. What about when the application is running? How does Serial.print() work? How can I read those?
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* framework-arduinoadafruitnrf52/cores/nRF5/TinyUSB/Adafruit_TinyUSB_ArduinoCore/Adafruit_USBD_CDC.h likely has the answer and it uses TinyUSB.
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* Reset button seems to be "configurable" to use pin 0.18. Do I need to pre-configure it or will resetting work with Adafruit's bootloader for putting it into flash mode by quickly resetting it twice?
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* In the [ItsyBitsy schematic](https://cdn-learn.adafruit.com/assets/assets/000/087/158/original/adafruit_products_schem.png?1579387035), it seems like the reset switch simply pulls P0.18 to gnd.
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*
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## Power input
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* When connected to USB, VBUS is 5V
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* The datasheet mentions 1.7V - 5.5V supply voltage
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* But there are two supply pins (page 79):
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* VDD handles 1.7 - 3.6V
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* VDDH handles 2.5 - 5.5V
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* So, when connecting to USB, do I need to bridge VBUS and VDDH high?
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* (page 65): "As a consequence, VBUS and either VDDH or VDD supplies are required for USB peripheral operation"
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## Bluetooth
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I got basic sketches working on the barebones e73c breakout, except the ones running bluetooth.
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I was able to deviry that the program hands exactly when it reaches the Bluefruit.begin() function.
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Googling suggests that it's missing a low frequency oscillating crystal.
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Details on oscillator on page 84.
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### How to enable the internal synthetic one?
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In [arduino-nRF5](https://github.com/sandeepmistry/arduino-nRF5/blob/master/boards.txt#L49) there is a menu in which we can select:
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- Crystal (-DUSE_LFXO)
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- RC (-DUSE_LFRC)
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- Synthetic (-DUSE_LFSYNT)
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Changing the following on framework-arduinoadafruitnrf52/variants/feather_nrf52840_express/variant.h made it work:
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```C
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// #define USE_LFXO // Board uses 32khz crystal for LF
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#define USE_LFRC // Board uses RC for LF
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```
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