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Pan & Tilt shield vs. Servo shield

Posted: Sun Jan 27, 2019 1:04 am
by kwiley
I saw the various posts about these shields, read their descriptions, and looked over their pinouts a bit. I think the similarities and differences are fairly clear at this point. If I understand correctly, the P&T shield drives up to three servos directly off the PWM GPIO pins and the Servo shield drives up to eight servos via I2C. What I don't understand is what advantage the P&T offers. Does it simply predate the Servo shield and became essentially redundant once the servo shield was developed, or does it provide some genuine advantage over the servo shield such that one might have a "decision" to make between the two shields?

What would I gain by choosing the P&T? What would I lose by choosing the Servo shield? The Servo shield's advantages are fairly obvious: five additional servos while simultaneously freeing up three GPIO lines (to say nothing of the fact that the LED shield ties up two servo lines, further motivating the Servo shield over the P&T). But the P&T's advantages are not yet clear to me. Have I overlooked something here?

(disregarding the fact that one can use both shields simultaneously, which I already realize).

Thanks.

Re: Pan & Tilt shield vs. Servo shield

Posted: Sun Jan 27, 2019 1:12 am
by kwagyeman
I built the shield so that you can power the OpenMV Cam and servos from a battery source along with having direct servo control. This is particularly useful for building a DIY Robocar where you want to measure an input pulse width to dead man switch you robot along with being able to do servo out. The normal servo shield just does output so it's not possible to read an ESCs state using it. Additionally, the normal servo shield doesn't release the servos when the program stops. It keeps going as long as it has power which is dangerous if your program crashes.

Re: Pan & Tilt shield vs. Servo shield

Posted: Sun Jan 27, 2019 1:53 am
by kwiley
Hmmm, so the servo shield can't read a given servo's position but the P&T can?

Re: Pan & Tilt shield vs. Servo shield

Posted: Sun Jan 27, 2019 11:39 am
by kwagyeman
If you want to do an interrupt on an I/O pin to measure thr pulse width of an RC controller you can't do that using the service shield since there's another chip in the way.