Servo motors can be used in many areas like RC modeling, robotics and control devices. They operate by applying PWM signal. By varying duty cycle we can change its rotating shaft angle. If deal with servo motors a lot you probably know that like any other device may be faulty or have flaws. So it is best to check them before installing. You can buy many types of servo testers for cheap, but Jan_Henrik decided to build one. His intent was to make it versatile.
Servo tester is built around Attiny45 microcontroller which is programmed in Arduino language. Servos may come with different signal wiring, so he added three jumpers to select proper connector layout. PWM duty cycle is controlled with potentiometer. If you place any other resistive device like LDR, or thermistor instead of potentiometer you can use it for controlling fan speed or open/close vent hole. So this is great device that can be put in an hour.