Different voltages for servo signal and power?

Other Hardware Motors, Mechanics, Power and CNC
1

I have a common Tower Pro micro servo. It works with a microcontroller with 3.0 V. Signal comes from a pwm able pin. Power comes from a 3 V pin, which I assume is in direct contact with the 3 V battery package. Is it possible to connect the servo power line to a 5 V power supply (with common ground with the 3 V supply) without messing up things with the pwm signal, which obviously is 3 V? I'd like more speed and torque from this servo, but still need to use the 3 V microcontroller.

2

I think that should work fine - assuming the servo is designed for 5v or more. You need to have the 5v GND connected to the 3v GND.

...R

3

So a 3V 1.2 ms signal will turn the servo to the same position as a 5 V 1.2 ms signal? I suspected that the pwm signal and the power voltage would have to be equal.
I haven't found info about the inner soul life of a servo, but I've thought that the pwm signal creates an analog voltage in a capacitor. The wider pulse, the higher voltage. And the motor tries to turn the inner potentiometer to same voltage. Perhaps I'm on right track, but perhaps the cap is charged from the power line, not from the pwm signal itself. And the pwm signal only opens a transistor and shuts it.

4

The voltage of the servo signal is irrelevant provided that it is high enough to trigger the servo circuit. If it works now with a 3V signal it will continue to work with a 3V signal.

Steve

5

slipstick:
The voltage of the servo signal is irrelevant provided that it is high enough to trigger the servo circuit. If it works now with a 3V signal it will continue to work with a 3V signal.

Steve

That doesn't follow - its not how most CMOS inputs work for instance, where the logic levels scale with
supply.

If there isn't a datasheet to answer this question, you can but try it out.

6

Hobby servos rarely have published datasheets with that sort of detail. But all those I've seen are intended to work with most RC receivers (they'd soon go out of business if they didn't). And many of the older receivers used TTL levels and many of the current ones use internal 3.3V regulators and produce signals around that voltage.

So you're certainly right in that if you really want to know for a specific example then you should test it, but I'm still going to bet that 3V will be fine in this case. But I might be wrong, it's happened before and it will again.

Steve