Anyone with PF control block and oscilloscope? (need to know the control signal voltage for PF servo motor)

[Ocelot]

Hi all,

I have been controlling PF motors from a Raspberry Pi with no problems. Recently I acquired a PF servo motor. I know that the servo motor is powered on the 9V and GND rails, and the position commands are PWM via C1 and C2. What I need to know is the voltage of the PWM signals, which is difficult for me as I don't own the PF control blocks. So, if anyone has an oscilloscope and the PF control blocks, I would be very grateful if you could record the PWM frequency, voltage, and duty cycle passed to a servo motor.

Apologies if this is already answered but I have tried searching and also read Philo's site; yet nowhere do I find the specs for the C1 and C2 signals.

[JopieK]

See this: 

 

So the motor voltage is 9V and as your Pi IO is 3.3V your control voltage should be 3.3V. That is why this guy uses that motor H-bridge: you send 3.3V PWM signals to it and it is translated to the 9V level by the mosfets inside it.

 

[David Lechner]

C1 and C2 are also 9V (battery voltage). On non-servo motors, C1 and C2 actually power the motor and the 9V and GND lines are not connected.

[Ocelot]

Thanks for the replies! I'll try C1 and C2 at 9V (it is quite strange to see control signals at the same voltage as the motor supply, but I guess it made sense with the modular PF system).

[JopieK]

For PF they only use four leads of course and want to make it very easy for kids wo connect. For NXT / EV3 this is entirely different, I guess it is also different for Boost / Powered Up / Spike where there are more leads available.

[Tcm0]

C1 and C2 are not control signals in the classical sense - they are direct voltages to drive a motor. The servo just translates these voltage to positions.