Optically isolated servo motor - Wiring (6n137 and 4N35)

I want to optically isolated the circuitry of motor servo of the synthetizer circuitry like these Bastl Module.

The reasons is simple; the ground of the servo create pollution for the modular synthetiser, it’s absolutly the same thing than a MIDI IO.

The goal is to create someting like that:

This Bastl modular is very nice but it’s not accurate for 12V servo and it’s not portable, my goal is to use servo motor at 10 feet distance from modular synthetizer…

There is my schematic, the servo motor fail. For this test, I use the Arduino exemple Arduino - Knob. Very simple code. The PWM do not pass over the optpcoupler

That’s all!
Thanks to help me to resolve that mistake of my life. ::slight_smile:

How about using a pullup resistor in the range suggested by the datasheet, 330 ohms to 4k. Lower is
going to be better for risetime, say 470 or 1k

[ I suspect the servo has an internal 10k pulldown or something like that, so a weak pullup
like 10k isn't useful ]

Hi,
Welcome to the Forum.

In the 4N35, how big is R4, I hope not R100 or 0.1Ohms?
Try 1K0, You know that you are inverting the signal between the Arduino and the servo.
With output od the Arduino HIGH, the LED conducts, the phototransistor conducts, the servo input is pulled to gnd.
And vice versa.
So your servo command from the pot will be reversed, but it should work.

What servo are you using, can you post a link to its specs please?

Can you post your test code please?

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Tom... :slight_smile:

TomGeorge:
Hi, Welcome to the Forum.

Hey thanks for your responses, it's my first time to require help just because I can't find any good informations or schematics about this problem.. So now, I think I will have good time here.

TomGeorge:
In the 4N35, how big is R4, I hope not R100 or 0.1Ohms?
Try 1K0, You know that you are inverting the signal between the Arduino and the servo.

The R4 is 100 Ohm, but I tryed 1k.. same think. For inverting signal, I really don't know how! The servo with the 4n35 does nothing, but with the 6N137, it does something realy wrong (like freeze).

TomGeorge:
What servo are you using, can you post a link to its specs please?

Servo is 5V FS5103R

TomGeorge:
Can you post your test code please?

The code is the Arduino Knob, just for testing the PWM through the opto

MarkT:
How about using a pullup resistor in the range suggested by the datasheet, 330 ohms to 4k. Lower is
going to be better for risetime, say 470 or 1k.

Hi Mark, thanks for your respond, about the pull up R4, I tryed many, like 100R to 100K!, same think. And for the R3, I tryed 100R, 270R, 470R, 1K and 10k! = fail. I tryed many arkward test, like voltage divider for the opto, voltage divide for the servo, voltage divider for my girlfriend etc.. same result; fail! :confused:

Will an inverted servo signal even work? Why not connect the positive signal from pin 4 of the opto to the servo and a 1k or so pulldown resistor to ground?

edgemoron:
Will an inverted servo signal even work? Why not connect the positive signal from pin 4 of the opto to the servo and a 1k or so pulldown resistor to ground?

Its a buffered logic output opto, not a slow phototransistor, so that cannot work. And yes its actually
an inverting one, which isn't obligatory (or even desirable) for fast logic-output optos, so needs the
input LED driven active-low.

Pin 9 via resistor to opto cathode, opto anode to Arduino +5V - that'll fix it.

Stick with 1k pullup on the output of the opto.

MarkT:
Pin 9 via resistor to opto cathode, opto anode to Arduino +5V - that'll fix it.
Stick with 1k pullup on the output of the opto.

That's the trick! 8)

It's working now.. Thanks. I drew a schematic about this and I hope than people (like me before) see this when it's time to pass PWM through an 10 MBd optocoupler like 6N137!