LFO proposal

bubzy · Posted: Mon Jan 28, 2013 5:21 am Post subject: LFO proposal

having worked a little with the SPI DAC on the arduino, it dawned on me today that a very nice "programmable" LFO could be built from it, you could have selectable waveforms, tempo control, trigger input (for sync)
and the thing that really interested me was the possibility of "drawing" a waveform, this could be acheived by breaking a wave into a selectable number of chunks, and then letting the user choose the output level of each of these, so that potentially any waveform is possible.
the only bummer might be displaying it, this could possibly be overcome by using the 128 pixel displays but i havent worked with those yet so unsure of how easy that would be.

dont know if anyone can be bothered to implement this or not, but its out there as an idea now, might have a go myself, when i clear this backlog....*checks backlog*...that may be some time. Very Happy

elmegil · Posted: Mon Jan 28, 2013 6:22 am Post subject:

I have a shield that is two MCP4922's, a TL074 and a TL072. The original intent was a foundational piece of MIDI2CV with the Arduino--the 4 outputs from the MCP4922's go to the TL074 for buffering, and two other digital pins go to the TL072 to generate gate/trigger out.

Then I sat and brainstormed what other things I could do with 4 CV outs and two digital outs.

LFO was one of the things. However, i hadn't really thought about it any further. The input for sync is a good idea...I don't have any room on my shield to add input buffering to protect the Arduino, but then again, I was going to make multiple shields for the MIDI purpose anyway...

edit: One thing this DOESN'T do is shifting or scaling of the waveform. So it's a 0 - 5V wave. Probably should rework the op amp outputs to not be simple buffers, but actually do some of that scaling. Smile

Skellz · Joined: Dec 31, 2008 Posts: 18 Location: Ireland

bubzy · Posted: Wed Mar 20, 2013 7:04 am Post subject:

yeah, that's kinda what I had in mind, just gotta wait for some time to have a go at it, busy with analog stuff right now Smile

bubzy · Posted: Mon Mar 25, 2013 3:55 am Post subject:

welp, I've done some reading, a lot of asking (thanks scott) and have a very simple prototype growing on the breadboard.

so far ive got 5 adjustable "points", I have a "curved" waveform available, "linear" and "square" will also be options on the board, it will have adjustable tempo and sync in, im guessing that with a sync in option the unit will take a few clock pulses, average them out and then draw the waveform based on the time between the pulses. theres a possibility that I could implement a 1/1 1/2 1/4 etc switch to have the waveform sync at a specified time not sure how useful that would be.

just an update anyway Smile

sneakthief · Joined: Jul 24, 2006 Posts: 569 Location: Berlin

If you haven't already, you should take a few cues from the Electric Druid:

http://www.electricdruid.net/forums.html?page=projects.lfo9

bubzy · Posted: Thu Mar 28, 2013 6:28 am Post subject:

http://www.youtube.com/watch?v=d66fnWJZleQ

diablojoy · Posted: Sun Apr 07, 2013 2:47 am Post subject:

bubzy · Posted: Mon Apr 08, 2013 6:32 am Post subject:

im trying to keep this simple, so I've decided against a lcd menu driven interface, and im sticking with led's for indication and a 3x7segment display for the BPM counter. it will have a clock out, also clock in (which should count and display BPM) using this as an EG is a nice idea, so ill look into adding a "one shot" mode with a trigger in, im also considering adding a "free" mode, that isn't constrained to a particular BPM and just "goes with the flow" Very Happy

BPM counter is working.
have the waveform looking neat now, with some efficiency improvements by storing the values in an array instead of working them out every cycle
(thanks Scott and blue)

there is a pushbutton now to "capture" the new waveform from the potentiometers, this allows for greater speed as the calculation for the interpolated values is done only once.

there are 4(I think) possible types of wave
a "square" wave, so just the peaks.
a "linear" wave, that interpolates in a direct line between points
a "round" wave that uses catmull spline interpolation.
and im sure theres another Very Happy

im at work so I cant look it up.
these will be selectable via a pushbutton.

more features and fun soon Smile

thanks for your interest.

added a pic of its current state (messy Razz

)

BHM3eOlCMAEeMv-[1].jpg

Description:

Filesize:

45.27 KB

Viewed:

11841 Time(s)