Digital servo tester


This servo tester is designed around a PIC12F675 controller to provide for precise and reliable pulse generation (pulse length: 1 ms – 2 ms). The internal chip oscillator is specified for a 1% frequency tolerance.

Additionally, this servo tester supports voltages from 4.8 V to 6 V covering a broad range of different servos and allowing to use the BEC feature of speed regulators (please make sure to use either BEC or an external power supply to avoid a short). You can configure the polarity of the servo control pulse with a respective jumper.

Finally, this servo tester allows you to use standard servos for a wide range of additional applications such as e.g. controlling pan and tilt cameras.


The PIC12F675 controller firmware is controlling the pulse generation and the user interface of the servo tester. The supply voltage of the controller (3.3 V) is generated by a low drop voltage regulator; running the controller at this voltage guarantees the internal oscillator’s precision and allows you to apply the various supply voltages to the tester.

However, this design requires a driver (transistor Q1) in order to adjust the voltage level from the controller’s output pin to the servo’s input. The power itself is directly feed into the servo.

The polarity of the servo control pulse is determined by jumper JP3. Please note that the LED is a bi-color type.

User interface

Using the servo tester is simple and intuitive. The servo tester features two operating modes: Manual-mode, which allows you to control the servo by turning P1 and to move the servo into the neutral position and Exercise-mode, which will make the servo tester move back and forth automatically. You can switch the mode by pushing S1. The build-in LED would indicate which mode the tester is in.

If you turn on the device the tester would be in Manual-mode by default and you can determine the pulse length by turning the pot P1. As long as the pulse length would be shorter than 1.45 ms or longer than 1.55 ms the LED will lit green. In order to easily find the neutral position, the LED color will change to "yellow" meaning that both colors will be visible when you enter the window from 1.45 ms to 1.55 ms. Once the pot is moved to the neutral position of 1.5 ms the LED color will turn to red. This design allows for hands-free neutral position allowing you to easily perform mechanical adjustments and such.

In Exercise-mode you would have two different speeds available. The LED will always blink red and the blinking frequency indicates speed selected: 0,25 s for a cycle from one end to the other is represented by 2 x blinks/s and 15 s for a cycle which would be coded by 2 s on, then 2 s off). You can select the speed by turning the pot P1: if a position in the left half would be selected then then the higher frequency would be selected and a position on the right half of the scale would translate into the lower speed operation.

Software Download

The current servo tester software (release 1.0) can be downloaded below. This firmware is provided as freeware, but only for private, non-commercial use.

Servotester kit and components

In the Store you will find a complete kit, the pcb only and a controller programmed with the latest firmware.


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