Servo control input voltage and capacitance

Discussion in 'The Projects Forum' started by mad1, Dec 14, 2010.

  1. mad1

    Thread Starter New Member

    Dec 14, 2010

    I'm considering using a servo to control the angle of a small (100g) solar array. This is for a demo project, in which I'll be using a Microsemi SmartFusion FPGA to drive the control signal of a small (Hitec HS-55 or Futaba S-3001/3004) servo.

    The FPGA IO's cannot go higher than 3.3V, 12mA

    The Hitec site says that 3-5V peak-to-peak is enough for the control signal - this is good.

    However, I'm concerned about the input capacitance of the servo control input - is there any data on what this ranges between? What do typical users of these (or other small and cheap) servos drive the control inputs with?

    Thanks for any help
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    Servos are controlled by pulses that repeat every 20ms. See

    An excerpt from the "Controlling Servos" section on this page follows:
    "Servos are controlled with a 5vdc positive-going variable pulse width that repeats every 20mS. The pulse length determines the servo output shaft position but the 20mS frame rate is not position critical. The frame rate does need to repeat at least every 20mS or it will lose power or even stutter. The servo was designed for pulse widths that vary from 1.0mS to 2.0mS, where 1.5mS is centered."
  3. mad1

    Thread Starter New Member

    Dec 14, 2010
    Thanks for your reply. I understand and know how servos are expected to work. However, my question is specific to the abovementioned Futaba and servos and has to do with minimum voltage and capacitance/impedance and I was looking for that specific information. The 5vdc mentioned in the linked article isn't a minimum control signal voltage, and in fact, contradicts the FAQ on the manufacturer's website (Hitec)