8 Servo Serial 727 - not getting servo response - new user

I just received my Pololu Serial 8-Servo Controller (assembled) and am experiencing no servo activity when I test using the Pololu Serial Transmitter V1.2 program.

I have a Hitec HS422 servo connected to port 0 and am powering via a 5-cell RC receiver ‘hump pack’. I receive acknowledgement of the commands via the LEDs but do not see any activity on the servo, including not twitching when power is initially turned on.

I have verified that I am in Pololu mode and have the reset jumper off.

I am assuming that like many of the problems discussed on the forums that I am experiencing too low of current for operating the controller and the servo from this small pack, but wanted to get a second opinion before I hack up a cable to run from either a PC power supply or larger subC-cell RC pack. This battery was sufficient for running two servos and the receiver in our nitro RCs, but I am guessing that the 727 wants more current.

I am including my test sequence that I have been using to have it verified as workable so that I may also rule out user error.

Two five byte commands sent via the Pololu Serial Transmitter

128 1 0 0 79

resulting in this acknowlegement

12:50:32 PM sent 80 01 00 00 4F
received:  80 '€'  01 ''  00 '  00 '  4F 'O'
12:50:46 PM sent 80 01 02 00 32
received:  80 '€'  01 ''  02 ''  00 '  32 '2'

Thank you, all, for your input to help a new user in this exciting technology!

DaveP in Ohio


The servo controller does not need much current (probably less than most RC receivers), so I don’t think the power supply is your problem. One easy thing you can do to try to get some response is to use Mini SSC II mode with its 3-byte commands. As soon as you send the first byte, it should send all servos to their center position. If that doesn’t work, can you attach a picture of your setup?

- Jan

I tried Mini SSC II mode and got the same results… LED indicates data sent, command echoed back using 255,0,0.

I thought maybe I had a bad servo since it had been a while since we had ran our cars and that particular servo was mounted on a non-running car, but got the same response on 2 more thought to be known good servos. I’m really suspecting that the battery pack may be tanked after setting for a few years and is only charging to enough current for the controller, but not the servos.

I’m going to see if I can find a compatible plug in my junk pile to connect 12V from a PC supply to the VIN.


Hi Dave,

This may be a silly question on my part, but how do you have your battery connected to the servo controller?

The servo power bus is not directly connected to the VIN pin, so you might just need to add a wire from your battery pack to the VSERVO pin. Ground is common on the controller board, but the traces connecting to the ground pin next to VIN are pretty small, so you might want to connect your battery ground to the GND pin next to VSERVO.

Sorry if you had already figured this out, but it was one of the first mistakes I made with a servo controller.


Well, not silly in the least… that was exactly my problem… for some reason I was convinced that the servo was also drawing power from VIN. I put a not-so-charged hump pack on servo power and got the responses that I expected.

Thank you both for your help!