Electrical – Attiny85, reading analog values from PIN3, reports 654 on idle

At first, I am not a hardware professional (starter) so be kind please.

I try to reuse a DENON operation board of a DVD-player with 9 buttons with a Attiny85 Digispark clone connected to PIN3 (see also picture below)

EDIT: About picture: "Sparkfun" must be "Digispark".

However, I can read the values of the buttons, the values seems to be very close so it difficult to detect which button is pressed.

But that's not the main problem/question, the problem is the idle value of analogRead function which I don't understand. The Arduino (IDE) language manual 'says' that it is a value between 0 and 1023. In this case it reports 654 on idle and above when a button is pressed. Tried also PIN1 and reports 1023 but doesn't detect any input (value doesn't change).

Questions:

1. Why does the analogRead function reports 654 (also when board
   disconnected)
2. Can I increase the resolution of these values to detect buttons more
   precisely/accurate?

Some code ( I made a USB debugger software solution to debug values via keyboard because there is no UART):

#include "types.h"              // Custom types
#include "TrinketHidCombo.h"    // Trinket USB lib


#define PIN_BUTTON_IN 3

void setDelay( uint16_t ms ) // usbsafe delay
{
  if( ms < 10 )
   { delay(ms); }
  else {
         uint16_t iSteps = ms / 4;

         while( iSteps-- )
         {
           usbIdle(); // We need to do this to keep the Windows USB driver 'sadisfied'
           delay(4);
         }  
       }
  usbIdle();
}  

void usbIdle()
{
  // do nothing, check if USB needs anything done
  TrinketHidCombo.poll();  
}

void usbStart()
{ 
  TrinketHidCombo.begin(); 
}

bool usbSendDebugHandshake()
{
  TrinketHidCombo.pressKey( 0, KEYCODE_F24 ); // press
  TrinketHidCombo.pressKey( 0, 0 ); // release
  setDelay(20);
  TKeyboardLEDState recLedState = usbGetKeyboardLedState();
  return ( recLedState.caps && recLedState.num && recLedState.scroll );
}

void usbDebug(const char* s, bool bLineFeed )
{
 static bool bUsbDebugHandshake = false;
 static bool bUsbDebugEnabled = false;

 if( !bUsbDebugEnabled && !bUsbDebugHandshake )
  { 
    //bUsbDebugHandshake = true;
    bUsbDebugEnabled = bUsbDebugHandshake = usbSendDebugHandshake(); 
  }  


 if(  bUsbDebugEnabled ) 
  { 
    (bLineFeed)?TrinketHidCombo.println( s ):TrinketHidCombo.print( s ); 
    usbIdle();
  }  
}  

void usbDebug(const char* s )
{ usbDebug( s, true ); }

void usbDebug( int i, bool bLineFeed )
{
  char buff[10]; //the ASCII of the integer will be stored in this char array
  memset(buff, 0, sizeof(buff));
  //itoa(i,buff,10); //(integer, yourBuffer, base)
  usbDebug( itoa(i,buff,10), bLineFeed );   
}  


void usbDebug( int i )
{ usbDebug( i, true ); }


TKeyboardLEDState usbGetKeyboardLedState()
{
  uint8_t iState = TrinketHidCombo.getLEDstate();
  TKeyboardLEDState tResult;
  tResult.caps = (iState & KB_LED_CAPS);
  tResult.num = (iState & KB_LED_NUM);
  tResult.scroll = (iState & KB_LED_SCROLL);

  return tResult;
}  

// Setup and main routine 
void setup()
{
  usbStart(); // First priority, start the USB device engine and enumerate

  pinMode(PIN_BUTTON_IN   , INPUT );
}

void loop() // Main program - main()
{
  // Button pressed?
  int iButton = analogRead(PIN_BUTTON_IN);
  usbDebug( "PRESSED: ", false );
  usbDebug( iButton );
  setDelay(1000);
}