LFO ? What ?

[Rob Strand]

Does the Moog Modular's 901B Oscillator's "Lo" mode count?

I was thinking of where "LFO" specifically originated.  We all use it without thinking about it but who started it?

The more I pondered over it the more I got to thinking the synth people started it.   Same goes for VCF and maybe even VCA.

I don't think the circuit elements or concepts are new but at some point these *terms* started to be part of the electronics lingo.   That 1964 patent I posted mentions "Low Frequency Oscillator"  but it doesn't coin it as the lingo-ized LFO.

[PRR]

.... my LFO waveforms were wrong.
Never happens with a proper benchtop scope.

If you are old enough, a "proper" benchtop 'scope is a single-ended cap-coupled pentode with about 2cps cutoff. (We didn't Hertz yet.)

Direct (DC) coupled scopes got affordable in the 1960s. So yes, before my time, but I trash-picked 'scopes as old as this awful movie I just watched. ("The Big Broadcast of 1937" from 1936, wtf?)

[Rob Strand]

.... my LFO waveforms were wrong.
Never happens with a proper benchtop scope.

If you are old enough, a "proper" benchtop 'scope is a single-ended cap-coupled pentode with about 2cps cutoff. (We didn't Hertz yet.)

Direct (DC) coupled scopes got affordable in the 1960s. So yes, before my time, but I trash-picked 'scopes as old as this awful movie I just watched. ("The Big Broadcast of 1937" from 1936, wtf?)

On a PC it's possible to undo the input filtering using an equalization filter in DSP (or ltspice).    PC-based audio test software (like speaker testing software) often has a scheme to measure the sound card response then apply a correction filter automatically.

[ElectricDruid]

Since LFOs and Arduinos have been mentioned in a couple of posts recently, does anyone (Tom?) have any script info for using an Arduino for generating basic waves like triangle?  I've found a few on the net (none here), and they involved other 'things' like DACs...I mean, just the arduino itself...I've had this Uno sitting here for a long time and no real use for it, it could make a neat function generator for the bench.

If you want to get an output direct from the Arduino, you're looking at either PWM or PDM as a "budget DAC" on a single pin. I know the Arduino has "Analog Out"s that use the PWM, but they're set for a very low frequency by default, which makes the filtering very difficult. However, it's possible to tweak that. Once you've got a high frequency PWM output, a simple filter will turn it back into an analog waveform. My earliest PIC-based LFOs worked like this and used a 19.5KHz PWM output. The recent ones use 31.25KHz PWM or a PDM at 2MHz, which makes life very simple for the filter since the output frequency is so far above the signal frequencies of interest (even a basic RC filter at 1KHz is going to cut a 2MHz signal a *lot* because it's so high).

Whether anyone has actually *done* this on Arduino, I don't know. It's *possible*, for sure, but maybe everyone did it the easy way and stuck a DAC on.

[GibsonGM]

Ok, thanks Tom. So in the end, it's probably just as easy (or easier) to do the dual-opamp 'square and triangle wave' rig than to mess with it!

I've used it to turn fans on & off around my wood stove based on a temp. sensor and those sorts of things, but nothing musical really.