The List

Here is the list of newbie gotchas I ran into when developing the trap-watch project. I will be adding more gotchas as I find them so watch this space....

Including Libraries like espvfsfat.h in Components

To include library files like espvfatfat.h in components, you have to REQUIRE the correct component in your components CMakeLists.txt file. For example, for the Fat Filesystem, the component to require is fatfs. You can then #include "esp_vfs_fat.h" in your component file.

Installing the right version of ESP-IDF

By default, the esp-idf installation instructions tell you to install the latest version (read latest including unstable version). I think it is a good idea, especially when you are starting out to use the stable version. To install the stable version, find the current stable version (will be listed as stable in the version menu on the left of the ESP-IDF docs page) and change to that version before you install.

# Clone the repository without initialising the submodules
git clone https://github.com/espressif/esp-idf.git
# Go into the directory
cd esp-idf
# Checkout the stable version
git checkout vX.X.X
# Initialise the submodules
git submodule update --init
# Install for an ESP32
./install.sh esp32

The finicky ESP32-CAM SD card

The SD card seems to be the most finicky thing on the ESP32-CAM board. Not helped by the fact that the high speed SPI port that the SD card is connected to has the flash LED and in my case the PIR sensor attached to it. I configured the SDMMC library to use a bus width of 1, but found that whenever I removed the power on the board, it would always fail to initialise the SD card.

D (2901) sdmmc_periph: slot=1 host_div=10 card_div=20 freq=400kHz
D (2911) sdmmc_periph: slot=1 width=1
D (2911) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2941) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2941) sdmmc_sd: CMD8 timeout; not an SD v2.00 card
D (2941) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2941) sdmmc_io: sdmmc_init_io: io_send_op_cond (1) returned 0x107; not IO card
D (2951) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2961) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2971) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2971) sdmmc_cmd: sdmmc_send_cmd_send_op_cond: sdmmc_send_app_cmd err=0x107
D (2981) sdmmc_common: send_op_cond timeout, trying MMC
D (2991) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2991) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (3001) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (3011) sdmmc_cmd: sdmmc_send_cmd_send_op_cond: sdmmc_send_app_cmd err=0x107
E (3011) sdmmc_common: sdmmc_init_ocr: send_op_cond (1) returned 0x107
D (3021) sdmmc_init: sdmmc_card_init: sdmmc_init_ocr returned 0x107
E (3031) vfs_fat_sdmmc: sdmmc_card_init failed (0x107).
E (3031) trap-watch: Got an error initialising SD card 0x107: ESP_ERR_TIMEOUT

Not only that, but then trying to flash the ES32-CAM with an SD card inserted failed and blinded me by constantly flashing the flash. Only after setting the width back to 4, removing the card during flashing did it come right again.

D (2911) sdmmc_periph: slot=1 host_div=10 card_div=20 freq=400kHz
D (2921) sdmmc_periph: slot=1 width=1
D (2921) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2951) sdmmc_sd: SDHC/SDXC card
D (2951) sdmmc_req: process_command_response: error 0x107  (status=00000100)
D (2951) sdmmc_io: sdmmc_init_io: io_send_op_cond (1) returned 0x107; not IO card
D (2981) sdmmc_common: host_ocr=0x40ff8000 card_ocr=0xc0ff8000
D (2981) sdmmc_common: sdmmc_card_init: host_ocr=40ff8000, card_ocr=c0ff8000
D (2981) sdmmc_init: sdmmc_card_init: card type is SD
D (2991) sdmmc_common: sdmmc_init_host_bus_width: using 4-bit bus
D (2991) sdmmc_periph: slot=1 width=4
D (2991) sdmmc_common: sdmmc_init_host_frequency: using 20000 kHz bus frequency
D (3001) sdmmc_periph: slot=1 host_div=8 card_div=0 freq=20000kHz
D (3011) vfs_fat_sdmmc: using pdrv=0
I (3021) SD Card: Filesystem mounted
Name: SU04G
Type: SDHC/SDXC
Speed: 20 MHz
Size: 3781MB

I also had to then configure the Flash pin pulldown to turn the flash off.

gpio_set_pull_mode(FLASH_PIN, GPIO_PULLDOWN_ONLY);

mDNS domain

When trying to access your ESP32 using mDNS, don't forget the .local domain name

$ ping trap-watch.local