Created Software and sketch configuration (markdown)

Software-and-sketch-configuration.md

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+- **NB! select next partition scheme for ESP32 in Arduino IDE Tools menu:** "Minimal SPIFFS (1.9 MB APP with OTA/190 KB SPIFFS)"
+  - for boards, which do not have this option, need to modify `~/.arduino15/packages/esp32/hardware/esp32/1.0.4/boards.txt` and add required partition option
+- **use 80 MHz ESP32 frequency** in Arduino SDK, it will prolong battery life when operating portable, higher CPU speed is not required, there are no CPU intensive operations
+- when setting up APRSDroid, use **"TNC (KISS)"** connection protocol in Connection Preferences -> Connection Protocol
+- go to esp32_loraprs.ino and make next changes based on your requirements in `initializeConfig()`
+  - set `cfg.IsClientMode` to `false` if you are planning to run server mode for APRS-IS iGate / Digipeater
+  - for server mode fill `cfg.WifiSsid` and `cfg.WifiKey` with your WiFI AP data
+  - for server mode fill `cfg.AprsLogin` and `cfg.AprsPass` with APRS-IS login callsign and pass
+  - for server mode fill `cfg.AprsFilter`, see http://www.aprs-is.net/javAPRSFilter.aspx for various formats, do not include `filter` directive, just space separated values
+  - change `cfg.LoraFreq` if you are planning to use different frequency or if planning to calibrate clients, currently it is set to **433.775MHz** as per https://vienna.iaru-r1.org/wp-content/uploads/2019/01/VIE19-C5-015-OEVSV-LORA-APRS-433-MHz.pdf
+- if you are planning to use different esp32 pinouts then modify config.h
+  - lora module SS, **CFG_LORA_PIN_SS**, GPIO_5
+  - lora module RST, **CFG_LORA_PIN_RST**, GPIO_26
+  - lora module DIO0, **CFG_LORA_PIN_DIO0**, GPIO_14
+- if you are planning to experiment with different bandwidths/spread factors then modify values in `initializeConfig()`, with current parameters APRS packet time on air is around **1-2 seconds** @ 292bps/36Bps, to decode with as lower level as possible with reasonable speed (comparable to 300bps HF APRS), use https://github.com/tanupoo/lorawan_toa or https://www.rfwireless-world.com/calculators/LoRa-Data-Rate-Calculator.html to make further calculations
+  - lora bandwidth `cfg.LoraBw`, 125 kHz (also tested with 20.6 KHz and SF9 with frequency correction)
+  - lora spread factor `cfg.LoraSf`, 12 (should decode down to -20dB, choosen with the goal for minimum signal decode)
+  - lora coding rate `cfg.LoraCodingRate`, 7
+  - lora output power `cfg.LoraPower`, 20 (max 20 dBm ~ 100mW, change to lower value if needed)
+  - sync word `cfg.LoraSync`, 0x34
+- consider minimum decode level based on on BW + SF and required throughput ![alt text](images/bandwidth_vs_sf.jpg)
+- uses LoRa **built-in checksum** calculation to drop broken packets
+- note, that there a is **significant frequency drift** on temperature changes for different modules
+  - you need to use **external TCXO** if you are planning to use modules for narrow bandwidths less than 125 kHz 
+  - or calibrate clients based on server frequency drift report by changing `cfg.LoraFreq`, for example, let client and server run for an 30-60 minutes and if server reports err: -1500, then set client frequency to about 1000 kHz less, e.g. instead of 433.775 set it to 433.774, this will give couple of additional dB
+  - alternatively automatic calibration could be done on server or client side by enabling automatic frequency correction by setting `cfg.EnableAutoFreqCorrection` to `true`, might be suitable for experiments where only one client is operating or if server broadcast messages, so clients can correct their frequency. Use it either on client side to tune all clients to server frequency if TX is enabled on iGate side or to tune server to single client for test purposes
+ - other useful options are
+   - `cfg.EnableSignalReport` set to `true` to enable signal report, it will be added as a comment to APRS-IS submitted location
+   - `cfg.EnablePersistentAprsConnection` set to `false` to avoid keeping connection open to APRS-IS
+   - `cfg.EnableRfToIs` set to `true` to forward RF traffic to APRS-IS
+   - `cfg.EnableIsToRf` set to `true` to forward APRS-IS traffic to RF, see also `cfg.AprsFilter` for traffic filtering
+   - `cfg.EnableRepeater` set to `true` to enable packet repeater
+   - `cfg.EnableBeacon` set to `true` to enable periodic beacons specified in `cfg.AprsRawBeacon` with period specified in `cfg.AprsRawBeaconPeriodMinutes` into RF and APRS-IS if `cfg.EnableRfToIs` is enabled
+   - `cfg.LoraUseIsr` set to `true` to enable LoRa incoming packet handling using interrupts in continous RX mode suitable for speech data, otherwise set to `false` for single packet polling mode