Building an adjustable low frequency PWM controller with Arduino I am looking for a way to create an adjustable PWM controller capable of modulation frequency from 0-100 (more preferably 0-1000) Hz, duty cycle from 0-100%, and able to accept a voltage range of 5-30V DC. I have looked through Sparkfun and Adafruit for product or PWM shields capable of this and I have yet to find one. Some servo shields can be programmed down to 50Hz and arduino itself can be slowed to like 30Hz using timer0 and timer1 changes. However none of these options make it easy to vary frequency and none of them can accept much more than 6V. 

I have searched far and wide and found a few interesting things:

1) http://www.instructables.com/id/The-ultimate-PWM-driver-for-many-applications/
 This instructable shows an analog un-sensored PWM driver. It would get the job done here however, I need a way to read my Frequency and Duty Cycle


2) https://www.electronicsblog.net/arduino-frequency-counterduty-cycle-meter/

Here there is a way using pulsein() and other arduino functions to read both frequency and duty cycle as seen above. But then this is also assuming you're PWM voltage is 5V. So maybe you use a 5V regulator on the signal into the arduino? Would something that simple work or would it skew the signal and prevent accurate measurements? 

Obviously, if anyone has a better idea I'm open to it. I've been searching for a solution for some time. The trouble really seems to be the low frequency PWM request.
The ATmega328 in the Arduino Uno has a 16-bit timer (Timer/Counter 1) which can do PWM. It has a prescaler that can divide by 1024.  The lowest frequency that it can generate is about 0.12 Hz:

16MHz / 1024 / 65535 / 2 = 0.1192 Hz


We change the PWM frequency by changing the "top" value. For higher frequencies, lower the top value, and/or pick a smaller prescaler.

(And, really, what does 0 Hz PWM even mean?!? :-)  

The duty cycle can vary from 0-100%, with the resolution changing with the specific frequency you generate.

As for the high-voltage... use a motor driver, or darlington, or hexfet, or whatever...

I'm confused as to why you're reading the frequency. With the 16MHz crystal, you set it and you get what you asked for (within the crystal tolerances, temperature, etc.)

At least, that's how I think it works.
Good luck!