Controling servo speed by slider

[DaveX]

Does the "thumbposition number that is received from Bluetooth device" come in as digits of a number?

If so, maybe you need to parse serial into a number per something like one of these:

@DaveX

• Serial Input Basics - updated by @Robin2 -- How to read serial input without blocking other code from running. (HT @DeltaG)
• Other Serial processing:
• pcRead by @gcjr -- one-character parsing diagnostic/control tool (w/ Simulation).
• Two ways communication between Python3 and Arduino
• (off-site: @nickgammon on serial)

or

@DaveX

Serial parsing RPN/Postfix:

• My adaptations of @nickgammon's state-machine parser into a switch-case single-letter post-fix parser for commands and numbers. E.g. 4500R 80S 3G or '123 24 /p`:
• V1: Simple RPN number and command parsing and
• V2: RPN 4 function calculator+commands
• V3: Serial control of Stepper speed, acceleration and motion control with RPN calc -- Use Serial to control a stepper with real-time adjustment of Acceleration, Maximum speed and Position, with 4-function calculator.

The critical tricks are collecting the digits into a number, and doing something with the number once you recognize you aren't getting digits any more. Some snippets:

    case '0' ... '9': // digits -- collect a series of them
      numberMode = true;
      currentValue *= 10;
      currentValue += c - '0';
      break;

  if ( ! ((c >= '0') && (c <= '9')) ) {
    completeNumber();
  }

void completeNumber() {
  if (numberMode) {
    Serial.print(currentValue);
    numberMode = false;
  }
}

But it really depends on how all the Bluetooth slider stuff sends the number.