This repository is a fork of the original goshante/ats20_ats_ex firmware, dedicated to custom modifications, bug fixes, and new features. All discussion regarding these new versions should take place here.

Your feedback and suggestions are welcome! Please, put a star on the repository to raise the firmware higher up on the global list. Thanks :)

You can find the original project here: goshante/ats20_ats_ex

This fork introduces two main branches of improvements over the original firmware:

1. Audio Pop/Click Elimination (Hardware & Software Mod): A modification that completely removes pops and clicks when switching modes. It requires a minor physical change to the receiver circuit.
2. MOD_NO_RDS Firmware Series: An alternative firmware branch where the RDS feature was removed to free up program space (from first modifications). This enabled the addition of new functionality, most notably a unified Favorites system for all bands (AM, FM, SSB, CW), along with dozens of other fixes and improvements in code.

Important: This audio improvement only affects the speaker output, as the headphone jack is connected before the amplifier.

I strongly recommend to connect the voltage divider as close to the pin as possible - use for this a two - 10kOm resistors. In order to eliminate possible interference with ADC readout distortion

Font, moving elements on the screen have been changed since version 5.0 - if you want to use the old mapping - use version 4.11 without long term support.

GET 4.11

General interface view in version 4.11

Key interface changes in the 5.x versions

Main Screen

Settings Screen

Screen examples in the 6.x versions

SSB Mode	Favorites List
Full Screen Layout	Settings Menu

This guide explains how to upload the firmware to your ATS-20(+) receiver using a Windows PC and the xLoader software

You will need two things: the programming software and the correct firmware file

1. Programming Software:

   • Download xLoader (Click the green "Code" button, then "Download ZIP". Extract the files to a folder on your computer)

2. Firmware File (.hex):

   • For flashing via USB, you only need the file without the bootloader
   • Click here to download: ATS_EX.ino.eightanaloginputs.hex (Click the link, then find the "Download raw file" button)

📌 Which File Should I Use?

• The ATS_EX.ino.eightanaloginputs.hex file is the correct one for updating your receiver's firmware over a standard USB connection using xLoader
• The ATS_EX.ino.with_bootloader.hex file is an advanced file used only for programming with an external ISP programmer (like a USBasp). Do not use this file with xLoader for a standard USB update
• Link for advanced users: With_bootloader

Most ATS-20(+) receivers use a CH340 chip for USB communication. If your computer does not recognize the receiver when you plug it in, you must install the driver. This is a one-time setup

• Download and install the CH340 driver from a reliable source, such as SparkFun's Guide

• Connect your ATS-20+ receiver directly to a USB port on your PC
• Power on the receiver

• Open Device Manager in Windows (you can search for it in the Start Menu)
• Expand the "Ports (COM & LPT)" section
• Note the COM port number assigned to your receiver (e.g., COM3, COM4). If no port appears, verify your driver installation and USB cable

1. Launch xLoader.exe from the folder where you extracted it

2. Configure the settings precisely as follows:

   • Hex file: Click the ... button and select the ATS_EX.ino.eightanaloginputs.hex file you downloaded
   • Device: Select Duemilanove/Nano(ATmega328). This is correct for most ATS-20+ boards, which use an old bootloader
   • COM Port: Select the port number you found in Device Manager
   • Baud rate: Set to 57600

   Your settings should look like this:

   

1. Click the Upload button
2. The receiver's lights may flash during the process. Wait for it to complete
3. xLoader will display a message like "29xxx bytes uploaded" at the bottom of the window when finished
4. Your receiver should restart automatically with the new firmware. If the screen shows "EEPROM RST" on the first boot, this is normal

Installation is complete!

Troubleshooting Tips

• Upload Fails or Times Out: Double-check that you have selected the correct COM port and that no other software (like a serial monitor) is using it. Try a different USB cable or port
• Still Fails: Some boards require you to press and release the receiver's RESET button just a moment before you click the "Upload" button in xLoader
• Using an Arduino Uno Board Profile: If your receiver has a newer bootloader (like an official Arduino Uno), you may need to select Uno(ATmega328) as the Device and 115200 as the Baud rate. However, 57600 is correct for the vast majority of ATS-20+

This manual provides a comprehensive overview of the ATS-20+ EX firmware's features and controls.

1. Core Concepts: Understanding the Interface
   • The "Active Command" Paradigm
2. Section 1: Main Screen Operations
   • Power Management & Screen Control
   • Frequency Tuning & Step Control
   • Volume Control & Mute
   • Band Navigation
   • Mode Switching (AM/SSB/CW)
3. Section 2: Advanced Reception Controls
   • SSB Mode Operation
   • CW (Morse Code) Mode Operation
   • Bandwidth (BW) Filter Adjustment
4. Section 3: System Functions
   • Station Scanning
   • Favorites Management
   • The Settings Menu: A Deep Dive
5. Section 4: Maintenance & Support
   • Factory Reset (EEPROM Reset)
6. Section 5: Experimental Features
   • CW (Morse Code) Decoder
7. Quick Reference Button Chart
   • Main Screen Operations Chart

The firmware's UI is based on the "Active Command" paradigm. This model allows the encoder to serve multiple purposes without complex menus.

• Default State: By default the encoder knob controls the frequency.
• Active Command: A short press on VOL+ STEP BW or BAND+ makes that function the "Active Command". The corresponding UI element becomes inverted and the encoder knob temporarily controls that function.

Example: Changing Volume

1. Short-press VOL+. The volume value becomes inverted.
2. Rotate the encoder to set the desired level.
3. Short-press the encoder button to exit immediately or simply wait 3 seconds for it to time out. The encoder will then revert to controlling the frequency.

• Screen Off Mode: A short press on the AGC button toggles the screen's power. The receiver continues to operate with minimal power drain significantly extending battery life.
• Wake Screen: If the screen is off (either manually or by timeout) press any button to wake it. The first press only reactivates the screen and does not trigger any other action.

• Tuning Step Selection:
  1. Short-press STEP. The "STEP" value on the display will be highlighted.
  2. Rotate the encoder to select the desired step size.
  3. Short-press the encoder button to confirm and exit or wait for the timeout.

• Quick Adjustment: Short-press VOL+ then rotate the encoder.
• Continuous Adjustment: Press and hold VOL+ or VOL-.
• Mute: Short-press VOL- to toggle mute. The volume level is replaced by " M".

• Quick Jump: Short-press BAND+ then rotate the encoder to jump between pre-defined bands.
• Seamless Tuning: Tune past the edge of the current band to automatically switch to the adjacent one. Note: This applies between AM/SW bands; tuning past the SW band edge will not roll over into the FM band.

• Short-press MODE to cycle through reception modes: AM → LSB/USB → CW → AM. This function is disabled on FM bands.

1. Enter SSB Mode: Use the MODE button until LSB or USB is displayed.
2. Sideband Selection: Press and hold the BW button for 1-2 seconds to switch between LSB and USB.
3. Two-Stage Tuning: SSB requires a two-stage process for clear audio:
   • Coarse Tune (Frequency): Select a large step (e.g. 1 kHz 5 kHz). Tune the main frequency until you hear intelligible but still high or low-pitched audio.
   • Fine-Tune (Clarifier): Select a small step (e.g. 10 Hz 50 Hz). Now tuning only adjusts the audio pitch to make voices sound natural without changing the main frequency.
4. Sync Feature: While in SSB mode press and hold the MODE button to toggle the Sync feature. An S indicator will appear when active. This engages the DSP's Automatic Frequency Control (AFC) to compensate for signal drift reducing fading and distortion.

1. Enter CW Mode: Use the MODE button to select CW.
2. CW Sideband: Press and hold BW to switch the reception sideband (L for LSB U for USB). This is a tool to eliminate nearby interference. The receiver will automatically adjust the frequency to keep the audible tone consistent.
3. Tuning: The receiver's CW pitch is adjustable via CWP setting (500-800 Hz). Tune the main frequency until the Morse code signal's tone matches the selected pitch. Tip: Use a narrow BW filter (e.g. 0.5 kHz) in CW mode to isolate the signal.

1. Short-press the BW button.
2. Rotate the encoder to change the filter width.
   • Narrower (e.g. 1.8 kHz): Rejects adjacent channel interference improving clarity in crowded bands.
   • Wider (e.g. 4.0 kHz): Provides better audio fidelity on strong clear signals.

• Enable First: In the Settings Menu (BAND-) set the SCN item to On.
• Start/Stop Scan: In AM or FM mode short-press the encoder button to start scanning. Press any button to stop.
• Scan Behavior: The receiver will scan within the current band boundaries (or full SW range for shortwave bands) using predefined seek thresholds optimized for each mode.

This feature saves a complete station profile: frequency, mode (AM/LSB/USB/CW/FM), and the precise BFO offset for SSB/CW signals. The system supports up to 20 favorite stations across all bands.

• To Save a Station:

  1. Tune to any station and adjust it for optimal reception (including fine-tuning the pitch in SSB/CW).
  2. Press and hold AGC. A "SAVED" confirmation will appear on the screen.
  3. Note: The system prevents saving duplicate entries (same frequency and mode).

• To Access and Use the Favorites List:

  1. Press and hold STEP to open the Favorites menu.
  2. Navigate: Rotate the encoder to scroll through your saved stations (3 stations per page).
  3. Tune: Highlight the desired station and short-press the encoder button. The receiver will instantly reconfigure itself to match all the favorite's saved parameters.
  4. Delete: To remove a station, highlight it in the list and press the BW button.
  5. Exit: To close the menu without tuning, short-press STEP. The menu also closes automatically after 10 seconds of inactivity.

The Settings Menu provides access to all advanced receiver configurations. Think of it as your control center for fine-tuning the radio's behavior to match your listening preferences and conditions.

How to Access:

• Enter: Short press BAND- button
• Exit: Short press BAND- again, or wait 10 seconds for auto-exit
• Important: All changes are automatically saved to EEPROM when you exit

Menu Structure:

• 5 pages with 6 settings each (30 settings total)
• Settings are arranged in a 2×3 grid on each page
• Current page number shown in header (e.g., "SETTINGS 1|5")

Navigation & Editing:

1. Select Item: Rotate the encoder to move between settings
   • Movement pattern depends on NAV setting (row-wise or column-wise)
2. Enter Edit Mode: Short-press the encoder button
   • A > marker appears next to the value
   • The setting is now ready to be changed
3. Change Value: Rotate the encoder while in Edit Mode
4. Confirm: Short-press encoder again to save and exit Edit Mode
5. Switch Pages: Short-press BAND+ to cycle through pages

💡 Beginner's Tip: Start with default values and change one setting at a time to understand its effect. You can always perform a factory reset if needed.

⚠️ Important Mode Display: Settings that are not applicable to the current operating mode will display as "---" instead of their value. This visual indicator helps you quickly identify which settings are active in your current mode, simplifying the configuration process.

📝 Mode-Dependent Settings: ATT, AVC, and SMA store different values for AM, LSB, and USB modes. When you switch modes, these values automatically change to match the current mode's stored settings.

🔧 Quick Setup Guide for New Users:

1. First time: Leave most settings at defaults
2. Set your region: Adjust DE (FM De-emphasis) for your location
3. Optimize display: Set SCR (brightness) for your environment
4. For weak signals: Enable AVC=5, SMA=12, SMT=20
5. For headphones: Set FMP=Off
6. Save battery: Set CPU=50% and DIS=15m

📝 Settings Memory:

• Global settings: Saved once for entire radio
• Mode-dependent: ATT, AVC, SMA saved separately per mode
• Band-specific: BFO calibration saved per band (28 values)
• Auto-save: Changes saved to EEPROM when exiting menu

📌 Key Technical Notes:

• Mode-Dependent Settings: ATT, AVC, and SMA values are stored separately for AM, LSB, and USB modes. The displayed value changes automatically when you switch modes.
• Band-Specific BFO: The BFO calibration is saved individually for each of the 28 bands, allowing precise crystal drift compensation per frequency range.
• Soft Mute Systems: AM and FM use completely independent soft mute implementations with different parameter ranges (SMA/SMT for AM, FSA/FST for FM).
• SW AFC: The SWA setting only activates on Shortwave bands (1.7-30 MHz) while in AM mode. It helps track drifting broadcast stations but should be disabled for SSB/CW.
• Navigation Styles: The NAV setting affects only the Settings menu navigation, not the main screen or Favorites list.
• Mode Indicators: Settings showing "---" are not functional in the current mode, helping you focus on relevant parameters only.

This procedure resets all settings, band states, and clears all saved favorites to factory defaults.

1. Power the receiver off.
2. Press and hold the encoder button.
3. While holding the button, power the receiver on.
4. The screen will display "EEPROM RESET". The reset is complete.

Alternative Method: If the encoder button is faulty, you can perform a reset by holding the AGC button during power-on instead.

⚠️ IMPORTANT: This feature requires hardware modification and disabling Favorites (ENABLE_FAVORITES 0) due to memory constraints (requires ~30KB flash).

The firmware includes an experimental CW decoder using a fixed-point Goertzel algorithm for real-time Morse code to text conversion directly on the OLED display.

Technical Implementation:

• Algorithm: Narrowband Goertzel detector (N=128 samples)
• Reference: Internal 1.1V ADC reference for improved weak signal detection
• Adaptive timing: Automatic WPM tracking (5-60 WPM range)
• Display: 6 lines of decoded text with automatic scrolling
• Input: Analog pin A6 with AC coupling

Required Hardware Modification:

Connect speaker output to A6 with proper biasing:

• AC Coupling: 2.2 µF capacitor in series with audio signal
• Bias Network:
  • R1: 390 kΩ from +3.48V to A6 (470 kΩ also acceptable, provides ~0.5V bias)
  • R2: 75 kΩ from A6 to GND
  • This creates optimal DC bias for the 1.1V internal reference

Circuit Diagram:

Operation Guide:

1. Enable in firmware: Set ENABLE_CW_DECODER 1 and ENABLE_FAVORITES 0 in Defines.h before compiling
2. Setup:
   • Switch to CW mode
   • Set CWP (CW Pitch) in settings to match expected tone (600-700 Hz recommended)
3. Activate decoder: Long-press MODE button to enter decoder view
4. Display shows:
   • Header: "CW DECODER" with live WPM reading
   • Main area: Decoded text (auto-scrolls after 6 lines)
5. Exit: Press any button to return to normal display

Performance Characteristics:

• Optimal reception: 600 Hz tone at 25-30 WPM
• Pitch options: 500, 600, 700, 800 Hz (selectable via CWP setting)
• Adaptive tracking: Automatically adjusts to speed variations
• Best results with:
  • Stable signals (S5 or stronger)
  • Narrow bandwidth filter (0.5-1.0 kHz)
  • Minimal QRM/QRN

Known Limitations:

• Requires clean audio signal (affected by noise and fading)
• May struggle with hand-sent code with irregular timing
• Cannot decode overlapping signals

Alternative Solution: For professional-grade decoding performance:

• Android App: Morse Expert by VE3NEA
• Provides superior algorithm, adjustable filters, and logging capabilities

Test Signal: For decoder testing at 600Hz, 30WPM try: A A A A A / T T T T T / E E E E E / N A N A N A / PARIS PARIS PARIS

Additional Technical Details:

Signal Processing Chain:

• ADC Sampling: Continuous sampling at ~71.4 Hz block rate (14ms per block)
• DC Offset Tracking: Adaptive high-pass filter with 256-sample time constant
• Goertzel Bins: Pre-computed coefficients for bins 0-32 (Q14 fixed-point)
• Signal Detection: Dual-filter envelope tracking:
  • Fast envelope: Immediate response for tone detection
  • Slow noise floor: 64-sample time constant for baseline estimation
  • Hysteresis margin: Dynamic threshold with 3dB separation

Morse Timing Engine:

• Dot length: Adaptive from 2-6 blocks (28-84ms)
• Dash/Dot ratio: ITU standard 3:1 with tolerance for hand-keying
• Letter gap: 1.5× dot length
• Word gap: 4.5× dot length
• Symbol timeout: 140ms auto-flush for incomplete characters

Decoder Features:

• Character set: Full alphabet (A-Z), numbers (0-9), slash (/)
• Pattern matching: 5-bit packed lookup table for efficient memory use
• Adaptive speed tracking:
  • Smoothing factor: 7/8 old + 1/8 new (prevents jitter)
  • WPM display updates every 5 decoded symbols
  • Speed range: 5-60 WPM with automatic adjustment

Memory Optimization:

• Buffer size: 128 samples (int16_t) for Goertzel processing
• Lookup table: 36 bytes for Morse patterns (compressed format)
• State machine: 24 bytes total for decoder state
• Display buffer: Direct write to OLED (no frame buffer)

Debug Mode: (When DEBUG_CW 1)

• Serial output at 9600 baud showing:
  • ADC range and DC offset
  • Detected dots/dashes with timing
  • Envelope and noise floor levels
  • Real-time WPM calculations

Hardware Notes:

• Why A6: This pin has no digital functions, dedicated ADC input
• Voltage divider values: Creates ~0.55V DC bias (center of 1.1V range)
• Capacitor value: 2.2µF provides -3dB at ~7Hz (blocks DC, passes audio)
• Input impedance: ~465kΩ (set by bias network)

(Applies when on the main listening screen)

If you encounter difficulties with the new versions, you can temporarily roll back and download the version you like best using:

https://github.com/diqezit/ats20_ats_ex/archive/<commit_hash>.zip

Where <commit_hash> is copied from the list of commits at: https://github.com/diqezit/ats20_ats_ex/commits/mod_no_rds/

This way you will get the firmware archive of the desired version.

Thank you.