Jameco has an easy to follow tutorial. The image below shows that a 1mSec pulse width sends the servo full left. 1.5mSec centers the it. 2mSecs move the servo full right. Jameco explains it all very well.
The servo tester has three setting:
MANUAL: allows the servo position to be adjusted with a knob.
CENTER: sets the servo to it's center position
SWEEP: continually sweeps the servo from it's MAX to MIN position (forever)
Connection is simple. One side of the servo tester is for power. The other side is where the servo under test conveniently plugs in.
So.... let's use a Tektronix MSO5104B oscilloscope to look at the output of the servo tester and see what the heck is going on. In the screen shot below the servo tester control knob is set to full left (minimum). Sure enough, the pulse width as measured by the scope is 915uSec. That's pretty darn close to the 1mSec width in the drawing above.
With the knob set to full right (maximum) the scope cursors show a pulse width of 2.14mSec; pretty close to the ideal 2mSec in the drawing.
Using the MSO5104B oscilloscope to zoom out on the signal we can see that the pulses repeat steadily every 20mSec. If you check the tutorial at Jameco you will know that is exactly what is expected.
Conclusion: Splurge the $1.50 USD and treat yourself to this handy device. It really helps to verify that a servo is actually working and in setting the movement limits on your project. Below are two short videos of the servo tester in action.
Here a short video where I use a Tektronix AFG3252C to send the control pulses to the servo. The AFG3252C has infinitely more flexibility, but cost a few dollars more than the eBay option.
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