Update

README.md

@@ -1,5 +1,7 @@
 # raspi-pico-aprs-tnc
-A TX-only [TNC](https://en.wikipedia.org/wiki/Terminal_node_controller) (Terminal Network Controller) to generate the AFSK audio tones for [APRS](https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System) (Automatic Packet Reporting System) messages using a Raspberry Pi Pico microcontroller board.
+A TX-only [TNC](https://en.wikipedia.org/wiki/Terminal_node_controller) (Terminal Network Controller) to generate the [AFSK](https://en.wikipedia.org/wiki/Frequency-shift_keying#Audio_FSK) audio tones for [APRS](https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System) (Automatic Packet Reporting System) messages using a [Raspberry Pi Pico](https://en.wikipedia.org/wiki/Raspberry_Pi) microcontroller board.
+
+An analog line-out audio signal will be produced at GPIO-pin 'GP0'. You can observe it by using a scope, listen to it by using an audio amp, or connect it to any RF transceiver to send it on the air (ham radio license required).
 
 Basically, this is the data/signal flow:
 
@@ -14,23 +16,27 @@ If you have already installed the Pico-SDK, set the `PICO_SDK_PATH` environment
 
 ## Hardware
 
-We just need a simple low-pass filter to extract the AFSK-signal from the PWM signal. Just connect GPIO-pin 'GP0' to a 1k resistor and the latter to a 47 nF cap.
+We just need a simple band-pass filter to extract the AFSK-signal from the PWM signal:
-The junction between the resistor and the cap is our signal output.
+
+![band-pass](https://github.com/eleccoder/raspi-pico-aprs-tnc/doc/schematic/band_pass_filter.png)
+
 
 ## Build the application
+
 ```
-(cd into the clone dir)
+(cd into the cloned dir)
 cmake -S . -B build
 cmake --build build
 ```
 
 ## Run the application
+
 ```
 cd build
-(copy any of the flash files 'aprs_pico.uf2' or 'aprs_pico.elf' to the Pico board)
+(flash 'aprs_pico.uf2' or 'aprs_pico.elf' to the Pico board as usual)
 ```
 
-The GPIO-pin 'GP0' is the line-out for the analog AFSK-signal. You can observe it by using a scope, listen to it by using an audio amp, or connect it to an HT to bring it on the air (ham radio license required).
+The GPIO-pin 'GP0' is the line-out for the analog AFSK-signal. You can observe it by using a scope, listen to it by using an audio amp, or connect it to any RF transceiver to send it on the air (ham radio license required).
 
 ## Modify the application
 
@@ -38,9 +44,9 @@ To send an APRS message of your choice, you have to modify the *main()* function
 
 ## TODO (Aug 2021)
 
+- [x] Thorough evaluation
 - [x] Send the APRS message on the console (USB or UART) rather than hard-coding
 - [x] Code documentation
 - [x] Show how to connect to a Baofeng HT
 - [x] PTT control for HTs
-- [x] Scope screenshots
+
-- [x] Schematic & Fritzings