Why is the circuit "stable" (ie. servo does not jitter) when i'm measuring the current ?
For the most effect you could have a Pi circuit like this on each servo.
so; even if i had switched over to the nRF24, i would have faced the exact same problem !
Frequently the case.If it doesn't work and you don't know why, well, trying "something else" is not so smart.
...try something else till it works is OK,...
ehm... isn't that the basis of the scientific method ? you don't know - but you guess* what it is, and then that guess is either validated or proven wrong, at which point you will then DO know (something).* = educated one, conjecture or theory...
Close. The scientific method is more like: propose a theory, design experiments that can test it. Definitely not "just try something". Repeatability is part of this.In your case, you concluded "not enough power due to the BT module". The simplest experiment to prove/disprove this would be to remove the BT module from the circuit, see if the jitter goes away. That's an experiment I don't see in your power supply tests. I expect it won't make a difference, if only because BT is designed to be low power, secondly because the power requirement of a BT (or NRF24) module is far less than that of a typical servo.
Your PCA9685 should be perfectly fine as it just provides the signal for the servo, not the power (unless you wire it totally wrong). If used with LEDs it can probably drive LEDs directly. An LED takes 10-20mA typically, a signal ideally no current, in reality maybe a few µA, should be <1mA. No problem there.
Pi filters work well. I'm using them mostly on the MCU side, to keep the noise of the motors out. That's when using a 12V circuit supplying power to a number of motors and projects. 12V supply, diode (Schottky for lower voltage drop but a 1N400x will do just fine), then Pi filter before the 12V-5V buck converter. The diode is to prevent back flow, really helps in my case even though I'm using 1.5 mm2 wires.
hmm, i'm not sure how to set that up since it's using a "servo controller" module.(i'd have to setup a whole PCB of support circuitry next to the PCA9685 module)
although, i just had a look at the datasheet for the PCA9685 and it's really meant for PWM-ing LEDs and not really servos.
That series diode is absolutely not needed for motors, or in most situations really. But when running nearly a dozen water pumps (brushless DC) and a handful of air pumps (probably brushed DC) on the same power supply you do get to see quite some noise.
Don't bother making your own coils, not worth your time. Basic inductors are really cheap. Ferrite core is far more efficient, you're not looking for perfection in this application - air coils are for things like HiFi sound applications.
Using a servo control module is irrelevant. It is the power feed to the servos not the signal that need decoupling. So:-power supply -> Pi circuit 1 -> +ve of servo 1power supply -> Pi circuit 2 -> +ve of servo 2power supply -> Pi circuit 3-> +ve of servo 3power supply -> Pi circuit 4-> +ve of servo 4and so on.
Again irrelevant it is equally suited to servos as it is to LEDs or anything else that needs PWM. Incidentally you can't set up the chip so that you can do LEDs on some channels and servos on others. It is a bit of a long winded explanation not worth going into but just stick to servos or LEDs per chip.
thing is the PCA9685 module handles the V+ (for each servo)
The main problem of Pi filters is the size. Big inductor, big capacitors.