Raspberry PWM out - a warning

General
1

I tried to use the pwm output with an opamp as a source for a 0-10V dimmer. I saw a short spike in the brightness from time to time, 10 - 15 minutes or so.
So i made a simple setup: Slider, a pwm output pin, a 1kOhm resistor and a 2µ2 Elko to ground. I monitored the output with a scope.

pwm screenshot
pwm screenshot1117×565 45.2 KB

The pwm output is not as stable as suggested. For sensitive applications a separate hardware must be used.

2

The standard node just uses software pwm so it can be affected by other things the pi is doing.
I don't use it myself but the alternative pigpiod node should be more stable as it uses hardware timing

3

Could somone please share his experience with that node?

4

Just try it yourself and let us all know if it helps :slight_smile:

5

I have run 4 servos at the same time using gpiod node - rock solid, vs constant jitter with gpio node with only one servo.

1 Like
6

I tried it now, looks much better!
Now i have 2 quetions:
1 - the requirements for the node point to a line in the rc.local file
The addon is

/usr/bin/pigpiod

Is this the same as in Raspi-Configuration, where the GPIO remote access can be activated / deactivated?

2 - The requirements point to a vulnerability in the setup of
/usr/bin/pigpiod -l
The -l option is explained to configure the program for local access only.
I tried this, seeing the node to say connection refused. After removing the -l option it worked. Is there a trick to get that running?

Kind regards
Alexander

7

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