"Pololu Micro Serial Servo Controller" not working

I got a little problem with the 8-port-servo-controller. I attached the servo-power (4-6V) and the VIN
(5-16V)-GND to a labratory power supply with 5V. The RS-232 serial input is connected to the serial interface of the PC.

If I connect a cable to one of the servo ports and look at an oscilloscope I see a nice
PWM signal, after setting the parameters, I can easily create with command 4 an
apropriate PWM signal from 0,3ms till 2,7ms. But as soon as I connect a servo to the
board, the orange (yellow) led is on and there is a constant 0V at the servo signal cable. If I then send a command for absolute position, on the oscilloscope a PWM-signal flashes, the servo
moves a bit, then suddenly, the servo-signal is constantly 0V again, and the servo moves
back a bit again.

With just the oscilloscope connected to one of the servo-outputs, everything looks fine,
but as soon as I attach the servo, the yellow led flashes.

I removed the servo-voltage connection, so only Vin is connected to 5 volt, and then with
attached servo I get some kind of PWM-signal with a servo attached, but only with 3V
height, so the servo doesnt move.

Do you have any suggestion to that problem? I have no idea anymore what could help.

Thanks a lot in advance,

3 days after sendig a support-mail I got now an answer to this question, unfortunatly I did the post already before receiving the answer per e-mail.

Anyway, here’s the answer:


Your problem is most likely caused by the power supply not being able
(or set) to deliver the necessary current. Thus, when the servo
wants to start moving, the voltage drops, and the microcontroller
resets. With the servo power disconnected, that resetting problem
goes away, but you are effectively trying to power the servo through
the signal line, which is why you see it attenuated (it has a 220-ohm
resistor in line with it for protection in such cases).

Please contact me if you have any other questions.

There was obviously a problem with the power supply. I connected the Servo Voltage to another power supply, and now it works without problems!

Thanks a lot!
Best regards from Austria