Arduino Nano LFO

LFO on an Arduino Nano

Objective

Create an Arduino Based LFO that can be used in a modular or modularish system. Originally I was hoping to create a full blown modular with the arduino, but soon realized that it would take a bit more work than I thought. Not impossible, but I was hoping to use the PWN pins that were available versus needing DAC/ADC stuff. I wanted simple pots to pins, and pins to LPF for analog outs.

And Blinky lights.

So a basic platform that you can optimize, and build out from, without having to work too hard doing that.

Challenges

The biggest limitation for arduino is that you get 6 PWM across its 3 timers. PWM and Timers are tied together. If you want to do interrupts using timers, you kinda have to balance that otherwise things get screwy. I am using Timer 1, so pins 9, 10 just did not work for PWM.

https://forum.arduino.cc/index.php?topic=426773.0

You certainly can get around this. For example, use a CD40106 for the LFO timer and run entirely on external interrupts. You actually might get better resolution doing this. But again, my goal was low part count.

So, with just 4 pwms, I settled for a pure LFO. With room for features. If you were so inclined, this could be used for a unit with very few parts. Pots, buttons, Leds, Resistors and a few Caps at most.

Also, the Analog inputs for arduino is not super high on resolution. You could do a Corse/fine...which technically you see in analog circuits too.

Features

TWO LFOs with 3 waveforms per channel.

• Waveform 1 (Selectable)
  • Sine
  • Triangle
  • Ramp up/down
  • Psycho LFO 1 and 2
• Square wave 50% duty
• Waveform 2 ( Triangle)

Button to select waveform

Interface

Improvements

There is room for improvement here.

• Fast Read on PWM

• Use DDS instead of timer countdowns

• Timer with countdowns has too fine of a resolution on slow counts and not enough in higher freq. Perhaps map the values rather than a linear (or exp map)

• Other waveforms

  • Square wave 25% duty
  • Square Wave Random duty
  • Square wave Bursty
  • Trapaziod waveform (pwm)
  • Folded triangle (pwm)

Shift button

• Sync
• EEPROM Setting storage for toggle
  • Do you expect to turn off your patch and have it turn back on the same way? Store off the toggle state to do this.