Improved documentation

README.md

@@ -36,7 +36,7 @@ In the upper section of main.cpp you can specify the modules that should be comp
 Please note: if MQTT is enabled it's still possible to deactivate it via webgui.
 
 ## Wiring (2 SPI-instances)
-A lot of wiring is necessary to get ESP32-Tonuino working. After my first experiments I soldered the stuff on a board in order to avoid wild-west-cabling. Especially for the interconnect between uC and uSD-card-reader make sure to use short wires (like 10cm or so)! Important: you can easily connect another I2S-DACs but just connecting them in parallel to the I2S-pins (DIN, BCLK, LRC). This is true for example if you plan to integrate a [line/headphone-pcb](https://www.adafruit.com/product/3678). In general, this runs fine. But unfortunately this board lacks of a headphone jack, that takes note if a plug is inserted or not. Best way is to use a [headphone jack](https://www.conrad.de/de/p/cliff-fcr1295-klinken-steckverbinder-3-5-mm-buchse-einbau-horizontal-polzahl-3-stereo-schwarz-1-st-705830.html) that has a pin that is set to GND, if there's no plug and vice versa. Using for example a MOSFET-circuit, this signal can be inverted in a way, that MAX98357.SD is pulled down to GND if there's a plug. Doing that will turn off the speaker immediately if there's a plug and vice versa. Have a look at the PCB-folder in order to view the detailed solution.
+A lot of wiring is necessary to get ESP32-Tonuino working. After my first experiments I soldered the stuff on a board in order to avoid wild-west-cabling. Especially for the interconnect between uC and uSD-card-reader make sure to use short wires (like 10cm or so)! Important: you can easily connect another I2S-DACs but just connecting them in parallel to the I2S-pins (DIN, BCLK, LRC). This is true for example if you plan to integrate a [line/headphone-pcb](https://www.adafruit.com/product/3678). In general, this runs fine. But unfortunately this board lacks of a headphone jack, that takes note if a plug is inserted or not. Best way is to use a [headphone jack](https://www.conrad.de/de/p/cliff-fcr1295-klinken-steckverbinder-3-5-mm-buchse-einbau-horizontal-polzahl-3-stereo-schwarz-1-st-705830.html) that has a pin that is set to GND, if there's no plug and vice versa. Using for example a MOSFET-circuit, this signal can be inverted in a way, that MAX98357.SD is pulled down to GND if there's a plug. Doing that will turn off the speaker immediately if there's a plug and vice versa. Have a look at the PCB-folder in order to view the detailed solution. Here's an example for such a [headphone-pcb)(https://github.com/biologist79/Tonuino-ESP32-I2S/tree/master/PCBs/Headphone%20with%20PCM5102a%20and%20TMD1308) that makes use of GND.
 
 | ESP32 (GPIO)  | Hardware              | Pin    | Comment                                                      |
 | ------------- | --------------------- | ------ | ------------------------------------------------------------ |
@@ -122,22 +122,21 @@ In this case RFID-reader + SD-reader share SPI's SCK, MISO and MOSI. But make su
 When using a develboard with for example SD-card-reader already integrated, the pinouts described above my not fit your needs; feel free to change them according your needs. Additionaly some boards may use one or some of the GPIOs I used for their internal purposes and that reason for are maybe not exposed via pin-headers. However, having them exposed doesn't mean they can be used without limits. This is because some GPIOs have to be logical LOW or HIGH at start for example and this is probably not the case when connecting stuff to it. Feel free to adjust the GPIOs proposed by me (but be adviced it could take a while to get it running). If you encounter problems please refer the board's manual first. <br />
 Keep in mind the RFID-lib I used is intended for default-SPI-pins only (SCK, MISO, MOSI). [Here](https://github.com/biologist79/Tonuino-ESP32-I2S/tree/master/Hardware-Plaforms/ESP32-A1S-Audiokit) I described a solution for a board with many GPIOs used internally and a very limited number of GPIOs exposed. That's why I had to use different SPI-GPIOs for RFID as well. Please note I used a slightly modified [RFID-lib](https://github.com/biologist79/Tonuino-ESP32-I2S/tree/master/Hardware-Plaforms/ESP32-A1S-Audiokit/lib/MFRC522) there.
 
-## Prerequisites
+## Prerequisites / tipps
 * choose if optional modules (MQTT, FTP, Neopixel) should be compiled/enabled
 * for debugging-purposes serialDebug can be set to ERROR, NOTICE, INFO or DEBUG.
 * make decision, if MQTT should be enabled (enableMqtt)
 * if yes, set the IP of the MQTT-server accordingly and check the MQTT-topics (states and commands)
-* in setup() RFID-cards can be statically linked to an action/file. Everything is stored in uC's NVS.
 * if Neopixel enabled: set NUM_LEDS to the LED-number of your Neopixel-ring and define the Neopixel-type using `#define CHIPSET`
-* please note: by using audiobook-mode any playlist-savings will be overwritten with every start unless the RFID-cards in setup() are commented out. Main way to link RFID to an action will be a webservice (still under development)
 * If you're using Arduino-IDE please make sure to change ESP32's partition-layout to `No OTA (2MB APP/2MB Spiffs)` as otherwise the sketch won't fit into the flash-memory.
-* compile and upload the sketch
 * Please keep in mind that working SD is mandatory. Unless `SD_NOT_MANDATORY_ENABLE` is not set, Tonuino will never fully start up if SD is not working. Only use `SD_NOT_MANDATORY_ENABLE` for debugging as for normal operational mode, not having SD working doesn't make sense.
 * If you want to monitor the battery-voltage, make sure to enable `MEASURE_BATTERY_VOLTAGE`. Make sure to use a voltage-divider as voltage of a LiPo is way too high. For my tests I connected VBat with a serial connection of 130k + 390k resistors (VBat--130k--X--390k--GND). X is the measure-point where to connect the GPIO to.
 * If you're using a headphone-pcb with a [headphone jack](https://www.conrad.de/de/p/cliff-fcr1295-klinken-steckverbinder-3-5-mm-buchse-einbau-horizontal-polzahl-3-stereo-schwarz-1-st-705830.html) that has a pin to indicate if there's a plug, you can use this signal along with the feature `HEADPHONE_ADJUST_ENABLE` to limit the maximum headphone-voltage automatically.
+* Enabling `SHUTDOWN_IF_SD_BOOT_FAILS` is really recommended if you run your Tonuino in battery-mode without having a restart-button exposed to the outside of the Tonuino's enclosure. Because otherwise there's no way to restart your Tonuino and the error-state will remain until battery is empty.
+* compile and upload the sketch
 
 ## Starting Tonuino-ESP32 first time
-After plugging in it takes a few seconds until neopixel indicates that Tonuino is ready (by four (slow) rotating LEDs). If uC was not able to connect to WiFi, an access-point (named Tonuino) is opened and after connecting this WiFi, a [configuration-Interface](http://192.168.4.1) is available. Enter WiFI-credentials + the hostname (Tonuio's name) and save them and restart the uC. Then reconnect to your "regular" WiFi. Now you're ready to go: start learning RFID-tags via GUI. To reach the GUI enter the IP stated in the serial console or use the hostname. For example if you're using a Fritzbox as router and entered tonuino as hostname, in your webbrowser tonuino.fritz.box should work. After running the rfid-learning, place your RFID-tag next to the RFID-reader and the music (or whatever else you defined) should start to play. While the playlist is generated, fast-rotating LEDs are shown to indicate, that Tonuino is busy. The more tracks a playlist/directory contains the longer this step takes. <br >
+After plugging in it takes a few seconds until neopixel indicates that Tonuino is ready (by four (slow) rotating white LEDs). If uC was not able to connect to WiFi, an access-point (named Tonuino) is opened and after connecting this WiFi, a [configuration-Interface](http://192.168.4.1) is available via webbrowser. Enter WiFI-credentials + the hostname (Tonuio's name), save them and restart the uC. Then reconnect to your "regular" WiFi. Now you're ready to go: start learning RFID-tags via GUI. To reach the GUI enter the IP stated in the serial console or use the hostname. For example if you're using a Fritzbox as router and entered tonuino as hostname in the previous configuration-step, in your webbrowser tonuino.fritz.box should work. After doing the rfid-learning, place your RFID-tag next to the RFID-reader and the music (or whatever else you choosed) should start to play. While the playlist is generated, fast-rotating LEDs are shown to indicate that Tonuino is busy. The more tracks a playlist/directory contains the longer this step takes. <br >
 Please note: hostname can be used to call webgui or FTP-server. I tested it with a Fritzbox 7490 and worked fine. Make sure you don't use a name that already exists in you local network (LAN).
 
 ## After Tonuino-ESP32 is connected to your WiFi
@@ -206,6 +205,7 @@ Indicates different things. Don't forget configuration of number of LEDs via #de
 * buttons locked: track-progress-LEDs coloured red
 * paused: track-progress-LEDs coloured orange
 * rewind: if single-track-loop is activated a LED-rewind is performed when restarting the given track
+* (Optional) Flashes three times red if battery-voltage is too low
 
 Please note: some Neopixels use a reversed addressing which leads to the 'problem', that all effects are shown
 counter clockwise. If you want to change that behaviour, just enable `NEOPIXEL_REVERSE_ROTATION`.