A compact receiver requires a simple but consistent user interface.

All parameters are updated immediately when adjusted, eliminating the need for an explicit ‘apply’ operation.

Frequency tuning resolution is defined by a dedicated step mode.

EEPROM storage is used only to restore parameters after power cycling.

The interface separates real-time control from persistence, keeping operation simple while maintaining flexibility.

1. Control Interface
 Input device: Rotary Encoder
 Actions:Rotate/Push/Double Push

2. Global Behavior
 All parameters are updated immediately when changed (live behavior)
 No explicit “apply” or “confirm” operation exists
 Parameter values are always active once adjusted
 Store current parameters to EEPROM for restoration after power cycling

3. Mode Switching Behavior

 Push→ Switch to Select Mode
 Double Push→ Store current parameters to EEPROM
  → Parameters are restored after power cycle
  → Switch to Select Mode
  → When MEM mode, store the frequency in the MEM channel
  → When SCN mode, going into Automatic scan mode

4. Mode List
 FREQ : Frequency
 STEP : Frequency Step
 MEM : Memory Channel
 SCN : Scan Channel
 VOL : Volume
 SQU : Squelch Level
 BAND : AM (air band) / FM
 B_W : AM band width
 F_COR : Crystal Frequency Calibration
 ACA : Automatic scan mode

5. Mode Specifications
 FREQ Mode
  Parameter : Receiving frequency
  Range : 118 – 136 MHz (AM) / 76 - 109 MHz (FM)
  Resolution: Defined by STEP mode
  Behavior : Changes immediately (live)

 STEP Mode
  Parameter : Frequency step size
  Options : 10Hz / 1kHz / 10kHz / 100kHz / 1MHz / 25 kHz
  Behavior : Defines increment/decrement step in FREQ mode

 VOL Mode
  Parameter : Audio volume
  Range : 0 - 63 
  Behavior : Immediate effect on audio output

 SQL Mode
  Parameter : Squelch threshold
  Range : 0 - 63
  Behavior : Audio muted below threshold level

 MEM Mode
  Parameter : Memory channel
  Range : CH0 – CH49
  Behavior : Select memory channel number / assign current frequency

 SCN Mode
  Parameter : Memory channel
  Behavior : Assign memory channel frequency

 BAND Mode
  Parameter : AM (air band 118 - 136 MHz) / FM (76 - 109MHz)

 B_W Mode
  Parameter : Si4732 AM band width
  Unit : 0 - 6 (0:6kHz,1:4kHz, 2:3kHz, 3:2kHz, 4:1kHz, 5:1.8kHz, 6:2.5kHz)

 F_COR Mode
  Parameter : Crystal frequency correction
  Unit : Frequency offset (±Hz for 25MHz of Si5351a)
  Behavior : Adjusts local oscillator accuracy

6. Frequency Control Rule
  Frequency increment/decrement is quantized by STEP setting
  Changing STEP immediately affects FREQ tuning resolution

7. Persistence Behavior
  EEPROM stores:
  Current parameters (mode-dependent)
  Stored values are:→ Restored automatically at power-on

  Automatic scanning
  Double Push on SCN mode → Automatic scanning mode
  Sweep MEM channels every 200mS, if there is signal, stay 1 Sec more.
  Signal detection (squelch open / RSSI threshold)